memcg, vmscan: do not attempt soft limit reclaim if it would not scan anything

[platform/adaptation/renesas_rcar/renesas_kernel.git] / mm / memcontrol.c

/* memcontrol.c - Memory Controller
 *
 * Copyright IBM Corporation, 2007
 * Author Balbir Singh <balbir@linux.vnet.ibm.com>
 *
 * Copyright 2007 OpenVZ SWsoft Inc
 * Author: Pavel Emelianov <xemul@openvz.org>
 *
 * Memory thresholds
 * Copyright (C) 2009 Nokia Corporation
 * Author: Kirill A. Shutemov
 *
 * Kernel Memory Controller
 * Copyright (C) 2012 Parallels Inc. and Google Inc.
 * Authors: Glauber Costa and Suleiman Souhlal
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */

#include <linux/res_counter.h>
#include <linux/memcontrol.h>
#include <linux/cgroup.h>
#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <linux/pagemap.h>
#include <linux/smp.h>
#include <linux/page-flags.h>
#include <linux/backing-dev.h>
#include <linux/bit_spinlock.h>
#include <linux/rcupdate.h>
#include <linux/limits.h>
#include <linux/export.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/spinlock.h>
#include <linux/eventfd.h>
#include <linux/sort.h>
#include <linux/fs.h>
#include <linux/seq_file.h>
#include <linux/vmalloc.h>
#include <linux/vmpressure.h>
#include <linux/mm_inline.h>
#include <linux/page_cgroup.h>
#include <linux/cpu.h>
#include <linux/oom.h>
#include "internal.h"
#include <net/sock.h>
#include <net/ip.h>
#include <net/tcp_memcontrol.h>

#include <asm/uaccess.h>

#include <trace/events/vmscan.h>

struct cgroup_subsys mem_cgroup_subsys __read_mostly;
EXPORT_SYMBOL(mem_cgroup_subsys);

#define MEM_CGROUP_RECLAIM_RETRIES      5
static struct mem_cgroup *root_mem_cgroup __read_mostly;

#ifdef CONFIG_MEMCG_SWAP
/* Turned on only when memory cgroup is enabled && really_do_swap_account = 1 */
int do_swap_account __read_mostly;

/* for remember boot option*/
#ifdef CONFIG_MEMCG_SWAP_ENABLED
static int really_do_swap_account __initdata = 1;
#else
static int really_do_swap_account __initdata = 0;
#endif

#else
#define do_swap_account         0
#endif


/*
 * Statistics for memory cgroup.
 */
enum mem_cgroup_stat_index {
        /*
         * For MEM_CONTAINER_TYPE_ALL, usage = pagecache + rss.
         */
        MEM_CGROUP_STAT_CACHE,          /* # of pages charged as cache */
        MEM_CGROUP_STAT_RSS,            /* # of pages charged as anon rss */
        MEM_CGROUP_STAT_RSS_HUGE,       /* # of pages charged as anon huge */
        MEM_CGROUP_STAT_FILE_MAPPED,    /* # of pages charged as file rss */
        MEM_CGROUP_STAT_SWAP,           /* # of pages, swapped out */
        MEM_CGROUP_STAT_NSTATS,
};

static const char * const mem_cgroup_stat_names[] = {
        "cache",
        "rss",
        "rss_huge",
        "mapped_file",
        "swap",
};

enum mem_cgroup_events_index {
        MEM_CGROUP_EVENTS_PGPGIN,       /* # of pages paged in */
        MEM_CGROUP_EVENTS_PGPGOUT,      /* # of pages paged out */
        MEM_CGROUP_EVENTS_PGFAULT,      /* # of page-faults */
        MEM_CGROUP_EVENTS_PGMAJFAULT,   /* # of major page-faults */
        MEM_CGROUP_EVENTS_NSTATS,
};

static const char * const mem_cgroup_events_names[] = {
        "pgpgin",
        "pgpgout",
        "pgfault",
        "pgmajfault",
};

static const char * const mem_cgroup_lru_names[] = {
        "inactive_anon",
        "active_anon",
        "inactive_file",
        "active_file",
        "unevictable",
};

/*
 * Per memcg event counter is incremented at every pagein/pageout. With THP,
 * it will be incremated by the number of pages. This counter is used for
 * for trigger some periodic events. This is straightforward and better
 * than using jiffies etc. to handle periodic memcg event.
 */
enum mem_cgroup_events_target {
        MEM_CGROUP_TARGET_THRESH,
        MEM_CGROUP_TARGET_SOFTLIMIT,
        MEM_CGROUP_TARGET_NUMAINFO,
        MEM_CGROUP_NTARGETS,
};
#define THRESHOLDS_EVENTS_TARGET 128
#define SOFTLIMIT_EVENTS_TARGET 1024
#define NUMAINFO_EVENTS_TARGET  1024

struct mem_cgroup_stat_cpu {
        long count[MEM_CGROUP_STAT_NSTATS];
        unsigned long events[MEM_CGROUP_EVENTS_NSTATS];
        unsigned long nr_page_events;
        unsigned long targets[MEM_CGROUP_NTARGETS];
};

struct mem_cgroup_reclaim_iter {
        /*
         * last scanned hierarchy member. Valid only if last_dead_count
         * matches memcg->dead_count of the hierarchy root group.
         */
        struct mem_cgroup *last_visited;
        unsigned long last_dead_count;

        /* scan generation, increased every round-trip */
        unsigned int generation;
};

/*
 * per-zone information in memory controller.
 */
struct mem_cgroup_per_zone {
        struct lruvec           lruvec;
        unsigned long           lru_size[NR_LRU_LISTS];

        struct mem_cgroup_reclaim_iter reclaim_iter[DEF_PRIORITY + 1];

        struct mem_cgroup       *memcg;         /* Back pointer, we cannot */
                                                /* use container_of        */
};

struct mem_cgroup_per_node {
        struct mem_cgroup_per_zone zoneinfo[MAX_NR_ZONES];
};

struct mem_cgroup_threshold {
        struct eventfd_ctx *eventfd;
        u64 threshold;
};

/* For threshold */
struct mem_cgroup_threshold_ary {
        /* An array index points to threshold just below or equal to usage. */
        int current_threshold;
        /* Size of entries[] */
        unsigned int size;
        /* Array of thresholds */
        struct mem_cgroup_threshold entries[0];
};

struct mem_cgroup_thresholds {
        /* Primary thresholds array */
        struct mem_cgroup_threshold_ary *primary;
        /*
         * Spare threshold array.
         * This is needed to make mem_cgroup_unregister_event() "never fail".
         * It must be able to store at least primary->size - 1 entries.
         */
        struct mem_cgroup_threshold_ary *spare;
};

/* for OOM */
struct mem_cgroup_eventfd_list {
        struct list_head list;
        struct eventfd_ctx *eventfd;
};

static void mem_cgroup_threshold(struct mem_cgroup *memcg);
static void mem_cgroup_oom_notify(struct mem_cgroup *memcg);

/*
 * The memory controller data structure. The memory controller controls both
 * page cache and RSS per cgroup. We would eventually like to provide
 * statistics based on the statistics developed by Rik Van Riel for clock-pro,
 * to help the administrator determine what knobs to tune.
 *
 * TODO: Add a water mark for the memory controller. Reclaim will begin when
 * we hit the water mark. May be even add a low water mark, such that
 * no reclaim occurs from a cgroup at it's low water mark, this is
 * a feature that will be implemented much later in the future.
 */
struct mem_cgroup {
        struct cgroup_subsys_state css;
        /*
         * the counter to account for memory usage
         */
        struct res_counter res;

        /* vmpressure notifications */
        struct vmpressure vmpressure;

        /*
         * the counter to account for mem+swap usage.
         */
        struct res_counter memsw;

        /*
         * the counter to account for kernel memory usage.
         */
        struct res_counter kmem;
        /*
         * Should the accounting and control be hierarchical, per subtree?
         */
        bool use_hierarchy;
        unsigned long kmem_account_flags; /* See KMEM_ACCOUNTED_*, below */

        bool            oom_lock;
        atomic_t        under_oom;

        int     swappiness;
        /* OOM-Killer disable */
        int             oom_kill_disable;

        /* set when res.limit == memsw.limit */
        bool            memsw_is_minimum;

        /* protect arrays of thresholds */
        struct mutex thresholds_lock;

        /* thresholds for memory usage. RCU-protected */
        struct mem_cgroup_thresholds thresholds;

        /* thresholds for mem+swap usage. RCU-protected */
        struct mem_cgroup_thresholds memsw_thresholds;

        /* For oom notifier event fd */
        struct list_head oom_notify;

        /*
         * Should we move charges of a task when a task is moved into this
         * mem_cgroup ? And what type of charges should we move ?
         */
        unsigned long   move_charge_at_immigrate;
        /*
         * set > 0 if pages under this cgroup are moving to other cgroup.
         */
        atomic_t        moving_account;
        /* taken only while moving_account > 0 */
        spinlock_t      move_lock;
        /*
         * percpu counter.
         */
        struct mem_cgroup_stat_cpu __percpu *stat;
        /*
         * used when a cpu is offlined or other synchronizations
         * See mem_cgroup_read_stat().
         */
        struct mem_cgroup_stat_cpu nocpu_base;
        spinlock_t pcp_counter_lock;

        atomic_t        dead_count;
#if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_INET)
        struct tcp_memcontrol tcp_mem;
#endif
#if defined(CONFIG_MEMCG_KMEM)
        /* analogous to slab_common's slab_caches list. per-memcg */
        struct list_head memcg_slab_caches;
        /* Not a spinlock, we can take a lot of time walking the list */
        struct mutex slab_caches_mutex;
        /* Index in the kmem_cache->memcg_params->memcg_caches array */
        int kmemcg_id;
#endif

        int last_scanned_node;
#if MAX_NUMNODES > 1
        nodemask_t      scan_nodes;
        atomic_t        numainfo_events;
        atomic_t        numainfo_updating;
#endif
        /*
         * Protects soft_contributed transitions.
         * See mem_cgroup_update_soft_limit
         */
        spinlock_t soft_lock;

        /*
         * If true then this group has increased parents' children_in_excess
         * when it got over the soft limit.
         * When a group falls bellow the soft limit, parents' children_in_excess
         * is decreased and soft_contributed changed to false.
         */
        bool soft_contributed;

        /* Number of children that are in soft limit excess */
        atomic_t children_in_excess;

        struct mem_cgroup_per_node *nodeinfo[0];
        /* WARNING: nodeinfo must be the last member here */
};

static size_t memcg_size(void)
{
        return sizeof(struct mem_cgroup) +
                nr_node_ids * sizeof(struct mem_cgroup_per_node);
}

/* internal only representation about the status of kmem accounting. */
enum {
        KMEM_ACCOUNTED_ACTIVE = 0, /* accounted by this cgroup itself */
        KMEM_ACCOUNTED_ACTIVATED, /* static key enabled. */
        KMEM_ACCOUNTED_DEAD, /* dead memcg with pending kmem charges */
};

/* We account when limit is on, but only after call sites are patched */
#define KMEM_ACCOUNTED_MASK \
                ((1 << KMEM_ACCOUNTED_ACTIVE) | (1 << KMEM_ACCOUNTED_ACTIVATED))

#ifdef CONFIG_MEMCG_KMEM
static inline void memcg_kmem_set_active(struct mem_cgroup *memcg)
{
        set_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_account_flags);
}

static bool memcg_kmem_is_active(struct mem_cgroup *memcg)
{
        return test_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_account_flags);
}

static void memcg_kmem_set_activated(struct mem_cgroup *memcg)
{
        set_bit(KMEM_ACCOUNTED_ACTIVATED, &memcg->kmem_account_flags);
}

static void memcg_kmem_clear_activated(struct mem_cgroup *memcg)
{
        clear_bit(KMEM_ACCOUNTED_ACTIVATED, &memcg->kmem_account_flags);
}

static void memcg_kmem_mark_dead(struct mem_cgroup *memcg)
{
        /*
         * Our caller must use css_get() first, because memcg_uncharge_kmem()
         * will call css_put() if it sees the memcg is dead.
         */
        smp_wmb();
        if (test_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_account_flags))
                set_bit(KMEM_ACCOUNTED_DEAD, &memcg->kmem_account_flags);
}

static bool memcg_kmem_test_and_clear_dead(struct mem_cgroup *memcg)
{
        return test_and_clear_bit(KMEM_ACCOUNTED_DEAD,
                                  &memcg->kmem_account_flags);
}
#endif

/* Stuffs for move charges at task migration. */
/*
 * Types of charges to be moved. "move_charge_at_immitgrate" and
 * "immigrate_flags" are treated as a left-shifted bitmap of these types.
 */
enum move_type {
        MOVE_CHARGE_TYPE_ANON,  /* private anonymous page and swap of it */
        MOVE_CHARGE_TYPE_FILE,  /* file page(including tmpfs) and swap of it */
        NR_MOVE_TYPE,
};

/* "mc" and its members are protected by cgroup_mutex */
static struct move_charge_struct {
        spinlock_t        lock; /* for from, to */
        struct mem_cgroup *from;
        struct mem_cgroup *to;
        unsigned long immigrate_flags;
        unsigned long precharge;
        unsigned long moved_charge;
        unsigned long moved_swap;
        struct task_struct *moving_task;        /* a task moving charges */
        wait_queue_head_t waitq;                /* a waitq for other context */
} mc = {
        .lock = __SPIN_LOCK_UNLOCKED(mc.lock),
        .waitq = __WAIT_QUEUE_HEAD_INITIALIZER(mc.waitq),
};

static bool move_anon(void)
{
        return test_bit(MOVE_CHARGE_TYPE_ANON, &mc.immigrate_flags);
}

static bool move_file(void)
{
        return test_bit(MOVE_CHARGE_TYPE_FILE, &mc.immigrate_flags);
}

/*
 * Maximum loops in mem_cgroup_hierarchical_reclaim(), used for soft
 * limit reclaim to prevent infinite loops, if they ever occur.
 */
#define MEM_CGROUP_MAX_RECLAIM_LOOPS            100

enum charge_type {
        MEM_CGROUP_CHARGE_TYPE_CACHE = 0,
        MEM_CGROUP_CHARGE_TYPE_ANON,
        MEM_CGROUP_CHARGE_TYPE_SWAPOUT, /* for accounting swapcache */
        MEM_CGROUP_CHARGE_TYPE_DROP,    /* a page was unused swap cache */
        NR_CHARGE_TYPE,
};

/* for encoding cft->private value on file */
enum res_type {
        _MEM,
        _MEMSWAP,
        _OOM_TYPE,
        _KMEM,
};

#define MEMFILE_PRIVATE(x, val) ((x) << 16 | (val))
#define MEMFILE_TYPE(val)       ((val) >> 16 & 0xffff)
#define MEMFILE_ATTR(val)       ((val) & 0xffff)
/* Used for OOM nofiier */
#define OOM_CONTROL             (0)

/*
 * Reclaim flags for mem_cgroup_hierarchical_reclaim
 */
#define MEM_CGROUP_RECLAIM_NOSWAP_BIT   0x0
#define MEM_CGROUP_RECLAIM_NOSWAP       (1 << MEM_CGROUP_RECLAIM_NOSWAP_BIT)
#define MEM_CGROUP_RECLAIM_SHRINK_BIT   0x1
#define MEM_CGROUP_RECLAIM_SHRINK       (1 << MEM_CGROUP_RECLAIM_SHRINK_BIT)

/*
 * The memcg_create_mutex will be held whenever a new cgroup is created.
 * As a consequence, any change that needs to protect against new child cgroups
 * appearing has to hold it as well.
 */
static DEFINE_MUTEX(memcg_create_mutex);

struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *s)
{
        return s ? container_of(s, struct mem_cgroup, css) : NULL;
}

/* Some nice accessors for the vmpressure. */
struct vmpressure *memcg_to_vmpressure(struct mem_cgroup *memcg)
{
        if (!memcg)
                memcg = root_mem_cgroup;
        return &memcg->vmpressure;
}

struct cgroup_subsys_state *vmpressure_to_css(struct vmpressure *vmpr)
{
        return &container_of(vmpr, struct mem_cgroup, vmpressure)->css;
}

struct vmpressure *css_to_vmpressure(struct cgroup_subsys_state *css)
{
        return &mem_cgroup_from_css(css)->vmpressure;
}

static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg)
{
        return (memcg == root_mem_cgroup);
}

/* Writing them here to avoid exposing memcg's inner layout */
#if defined(CONFIG_INET) && defined(CONFIG_MEMCG_KMEM)

void sock_update_memcg(struct sock *sk)
{
        if (mem_cgroup_sockets_enabled) {
                struct mem_cgroup *memcg;
                struct cg_proto *cg_proto;

                BUG_ON(!sk->sk_prot->proto_cgroup);

                /* Socket cloning can throw us here with sk_cgrp already
                 * filled. It won't however, necessarily happen from
                 * process context. So the test for root memcg given
                 * the current task's memcg won't help us in this case.
                 *
                 * Respecting the original socket's memcg is a better
                 * decision in this case.
                 */
                if (sk->sk_cgrp) {
                        BUG_ON(mem_cgroup_is_root(sk->sk_cgrp->memcg));
                        css_get(&sk->sk_cgrp->memcg->css);
                        return;
                }

                rcu_read_lock();
                memcg = mem_cgroup_from_task(current);
                cg_proto = sk->sk_prot->proto_cgroup(memcg);
                if (!mem_cgroup_is_root(memcg) &&
                    memcg_proto_active(cg_proto) && css_tryget(&memcg->css)) {
                        sk->sk_cgrp = cg_proto;
                }
                rcu_read_unlock();
        }
}
EXPORT_SYMBOL(sock_update_memcg);

void sock_release_memcg(struct sock *sk)
{
        if (mem_cgroup_sockets_enabled && sk->sk_cgrp) {
                struct mem_cgroup *memcg;
                WARN_ON(!sk->sk_cgrp->memcg);
                memcg = sk->sk_cgrp->memcg;
                css_put(&sk->sk_cgrp->memcg->css);
        }
}

struct cg_proto *tcp_proto_cgroup(struct mem_cgroup *memcg)
{
        if (!memcg || mem_cgroup_is_root(memcg))
                return NULL;

        return &memcg->tcp_mem.cg_proto;
}
EXPORT_SYMBOL(tcp_proto_cgroup);

static void disarm_sock_keys(struct mem_cgroup *memcg)
{
        if (!memcg_proto_activated(&memcg->tcp_mem.cg_proto))
                return;
        static_key_slow_dec(&memcg_socket_limit_enabled);
}
#else
static void disarm_sock_keys(struct mem_cgroup *memcg)
{
}
#endif

#ifdef CONFIG_MEMCG_KMEM
/*
 * This will be the memcg's index in each cache's ->memcg_params->memcg_caches.
 * There are two main reasons for not using the css_id for this:
 *  1) this works better in sparse environments, where we have a lot of memcgs,
 *     but only a few kmem-limited. Or also, if we have, for instance, 200
 *     memcgs, and none but the 200th is kmem-limited, we'd have to have a
 *     200 entry array for that.
 *
 *  2) In order not to violate the cgroup API, we would like to do all memory
 *     allocation in ->create(). At that point, we haven't yet allocated the
 *     css_id. Having a separate index prevents us from messing with the cgroup
 *     core for this
 *
 * The current size of the caches array is stored in
 * memcg_limited_groups_array_size.  It will double each time we have to
 * increase it.
 */
static DEFINE_IDA(kmem_limited_groups);
int memcg_limited_groups_array_size;

/*
 * MIN_SIZE is different than 1, because we would like to avoid going through
 * the alloc/free process all the time. In a small machine, 4 kmem-limited
 * cgroups is a reasonable guess. In the future, it could be a parameter or
 * tunable, but that is strictly not necessary.
 *
 * MAX_SIZE should be as large as the number of css_ids. Ideally, we could get
 * this constant directly from cgroup, but it is understandable that this is
 * better kept as an internal representation in cgroup.c. In any case, the
 * css_id space is not getting any smaller, and we don't have to necessarily
 * increase ours as well if it increases.
 */
#define MEMCG_CACHES_MIN_SIZE 4
#define MEMCG_CACHES_MAX_SIZE 65535

/*
 * A lot of the calls to the cache allocation functions are expected to be
 * inlined by the compiler. Since the calls to memcg_kmem_get_cache are
 * conditional to this static branch, we'll have to allow modules that does
 * kmem_cache_alloc and the such to see this symbol as well
 */
struct static_key memcg_kmem_enabled_key;
EXPORT_SYMBOL(memcg_kmem_enabled_key);

static void disarm_kmem_keys(struct mem_cgroup *memcg)
{
        if (memcg_kmem_is_active(memcg)) {
                static_key_slow_dec(&memcg_kmem_enabled_key);
                ida_simple_remove(&kmem_limited_groups, memcg->kmemcg_id);
        }
        /*
         * This check can't live in kmem destruction function,
         * since the charges will outlive the cgroup
         */
        WARN_ON(res_counter_read_u64(&memcg->kmem, RES_USAGE) != 0);
}
#else
static void disarm_kmem_keys(struct mem_cgroup *memcg)
{
}
#endif /* CONFIG_MEMCG_KMEM */

static void disarm_static_keys(struct mem_cgroup *memcg)
{
        disarm_sock_keys(memcg);
        disarm_kmem_keys(memcg);
}

static void drain_all_stock_async(struct mem_cgroup *memcg);

static struct mem_cgroup_per_zone *
mem_cgroup_zoneinfo(struct mem_cgroup *memcg, int nid, int zid)
{
        VM_BUG_ON((unsigned)nid >= nr_node_ids);
        return &memcg->nodeinfo[nid]->zoneinfo[zid];
}

struct cgroup_subsys_state *mem_cgroup_css(struct mem_cgroup *memcg)
{
        return &memcg->css;
}

static struct mem_cgroup_per_zone *
page_cgroup_zoneinfo(struct mem_cgroup *memcg, struct page *page)
{
        int nid = page_to_nid(page);
        int zid = page_zonenum(page);

        return mem_cgroup_zoneinfo(memcg, nid, zid);
}

/*
 * Implementation Note: reading percpu statistics for memcg.
 *
 * Both of vmstat[] and percpu_counter has threshold and do periodic
 * synchronization to implement "quick" read. There are trade-off between
 * reading cost and precision of value. Then, we may have a chance to implement
 * a periodic synchronizion of counter in memcg's counter.
 *
 * But this _read() function is used for user interface now. The user accounts
 * memory usage by memory cgroup and he _always_ requires exact value because
 * he accounts memory. Even if we provide quick-and-fuzzy read, we always
 * have to visit all online cpus and make sum. So, for now, unnecessary
 * synchronization is not implemented. (just implemented for cpu hotplug)
 *
 * If there are kernel internal actions which can make use of some not-exact
 * value, and reading all cpu value can be performance bottleneck in some
 * common workload, threashold and synchonization as vmstat[] should be
 * implemented.
 */
static long mem_cgroup_read_stat(struct mem_cgroup *memcg,
                                 enum mem_cgroup_stat_index idx)
{
        long val = 0;
        int cpu;

        get_online_cpus();
        for_each_online_cpu(cpu)
                val += per_cpu(memcg->stat->count[idx], cpu);
#ifdef CONFIG_HOTPLUG_CPU
        spin_lock(&memcg->pcp_counter_lock);
        val += memcg->nocpu_base.count[idx];
        spin_unlock(&memcg->pcp_counter_lock);
#endif
        put_online_cpus();
        return val;
}

static void mem_cgroup_swap_statistics(struct mem_cgroup *memcg,
                                         bool charge)
{
        int val = (charge) ? 1 : -1;
        this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_SWAP], val);
}

static unsigned long mem_cgroup_read_events(struct mem_cgroup *memcg,
                                            enum mem_cgroup_events_index idx)
{
        unsigned long val = 0;
        int cpu;

        for_each_online_cpu(cpu)
                val += per_cpu(memcg->stat->events[idx], cpu);
#ifdef CONFIG_HOTPLUG_CPU
        spin_lock(&memcg->pcp_counter_lock);
        val += memcg->nocpu_base.events[idx];
        spin_unlock(&memcg->pcp_counter_lock);
#endif
        return val;
}

static void mem_cgroup_charge_statistics(struct mem_cgroup *memcg,
                                         struct page *page,
                                         bool anon, int nr_pages)
{
        preempt_disable();

        /*
         * Here, RSS means 'mapped anon' and anon's SwapCache. Shmem/tmpfs is
         * counted as CACHE even if it's on ANON LRU.
         */
        if (anon)
                __this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_RSS],
                                nr_pages);
        else
                __this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_CACHE],
                                nr_pages);

        if (PageTransHuge(page))
                __this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_RSS_HUGE],
                                nr_pages);

        /* pagein of a big page is an event. So, ignore page size */
        if (nr_pages > 0)
                __this_cpu_inc(memcg->stat->events[MEM_CGROUP_EVENTS_PGPGIN]);
        else {
                __this_cpu_inc(memcg->stat->events[MEM_CGROUP_EVENTS_PGPGOUT]);
                nr_pages = -nr_pages; /* for event */
        }

        __this_cpu_add(memcg->stat->nr_page_events, nr_pages);

        preempt_enable();
}

unsigned long
mem_cgroup_get_lru_size(struct lruvec *lruvec, enum lru_list lru)
{
        struct mem_cgroup_per_zone *mz;

        mz = container_of(lruvec, struct mem_cgroup_per_zone, lruvec);
        return mz->lru_size[lru];
}

static unsigned long
mem_cgroup_zone_nr_lru_pages(struct mem_cgroup *memcg, int nid, int zid,
                        unsigned int lru_mask)
{
        struct mem_cgroup_per_zone *mz;
        enum lru_list lru;
        unsigned long ret = 0;

        mz = mem_cgroup_zoneinfo(memcg, nid, zid);

        for_each_lru(lru) {
                if (BIT(lru) & lru_mask)
                        ret += mz->lru_size[lru];
        }
        return ret;
}

static unsigned long
mem_cgroup_node_nr_lru_pages(struct mem_cgroup *memcg,
                        int nid, unsigned int lru_mask)
{
        u64 total = 0;
        int zid;

        for (zid = 0; zid < MAX_NR_ZONES; zid++)
                total += mem_cgroup_zone_nr_lru_pages(memcg,
                                                nid, zid, lru_mask);

        return total;
}

static unsigned long mem_cgroup_nr_lru_pages(struct mem_cgroup *memcg,
                        unsigned int lru_mask)
{
        int nid;
        u64 total = 0;

        for_each_node_state(nid, N_MEMORY)
                total += mem_cgroup_node_nr_lru_pages(memcg, nid, lru_mask);
        return total;
}

static bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg,
                                       enum mem_cgroup_events_target target)
{
        unsigned long val, next;

        val = __this_cpu_read(memcg->stat->nr_page_events);
        next = __this_cpu_read(memcg->stat->targets[target]);
        /* from time_after() in jiffies.h */
        if ((long)next - (long)val < 0) {
                switch (target) {
                case MEM_CGROUP_TARGET_THRESH:
                        next = val + THRESHOLDS_EVENTS_TARGET;
                        break;
                case MEM_CGROUP_TARGET_SOFTLIMIT:
                        next = val + SOFTLIMIT_EVENTS_TARGET;
                        break;
                case MEM_CGROUP_TARGET_NUMAINFO:
                        next = val + NUMAINFO_EVENTS_TARGET;
                        break;
                default:
                        break;
                }
                __this_cpu_write(memcg->stat->targets[target], next);
                return true;
        }
        return false;
}

/*
 * Called from rate-limitted memcg_check_events when enough
 * MEM_CGROUP_TARGET_SOFTLIMIT events are accumulated and it makes sure
 * that all the parents up the hierarchy will be noticed that this group
 * is in excess or that it is not in excess anymore. mmecg->soft_contributed
 * makes the transition a single action whenever the state flips from one to
 * other.
 */
static void mem_cgroup_update_soft_limit(struct mem_cgroup *memcg)
{
        unsigned long long excess = res_counter_soft_limit_excess(&memcg->res);
        struct mem_cgroup *parent = memcg;
        int delta = 0;

        spin_lock(&memcg->soft_lock);
        if (excess) {
                if (!memcg->soft_contributed) {
                        delta = 1;
                        memcg->soft_contributed = true;
                }
        } else {
                if (memcg->soft_contributed) {
                        delta = -1;
                        memcg->soft_contributed = false;
                }
        }

        /*
         * Necessary to update all ancestors when hierarchy is used
         * because their event counter is not touched.
         */
        while (delta && (parent = parent_mem_cgroup(parent)))
                atomic_add(delta, &parent->children_in_excess);
        spin_unlock(&memcg->soft_lock);
}

/*
 * Check events in order.
 *
 */
static void memcg_check_events(struct mem_cgroup *memcg, struct page *page)
{
        preempt_disable();
        /* threshold event is triggered in finer grain than soft limit */
        if (unlikely(mem_cgroup_event_ratelimit(memcg,
                                                MEM_CGROUP_TARGET_THRESH))) {
                bool do_softlimit;
                bool do_numainfo __maybe_unused;

                do_softlimit = mem_cgroup_event_ratelimit(memcg,
                                                MEM_CGROUP_TARGET_SOFTLIMIT);
#if MAX_NUMNODES > 1
                do_numainfo = mem_cgroup_event_ratelimit(memcg,
                                                MEM_CGROUP_TARGET_NUMAINFO);
#endif
                preempt_enable();

                mem_cgroup_threshold(memcg);
                if (unlikely(do_softlimit))
                        mem_cgroup_update_soft_limit(memcg);
#if MAX_NUMNODES > 1
                if (unlikely(do_numainfo))
                        atomic_inc(&memcg->numainfo_events);
#endif
        } else
                preempt_enable();
}

struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p)
{
        /*
         * mm_update_next_owner() may clear mm->owner to NULL
         * if it races with swapoff, page migration, etc.
         * So this can be called with p == NULL.
         */
        if (unlikely(!p))
                return NULL;

        return mem_cgroup_from_css(task_css(p, mem_cgroup_subsys_id));
}

struct mem_cgroup *try_get_mem_cgroup_from_mm(struct mm_struct *mm)
{
        struct mem_cgroup *memcg = NULL;

        if (!mm)
                return NULL;
        /*
         * Because we have no locks, mm->owner's may be being moved to other
         * cgroup. We use css_tryget() here even if this looks
         * pessimistic (rather than adding locks here).
         */
        rcu_read_lock();
        do {
                memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
                if (unlikely(!memcg))
                        break;
        } while (!css_tryget(&memcg->css));
        rcu_read_unlock();
        return memcg;
}

static enum mem_cgroup_filter_t
mem_cgroup_filter(struct mem_cgroup *memcg, struct mem_cgroup *root,
                mem_cgroup_iter_filter cond)
{
        if (!cond)
                return VISIT;
        return cond(memcg, root);
}

/*
 * Returns a next (in a pre-order walk) alive memcg (with elevated css
 * ref. count) or NULL if the whole root's subtree has been visited.
 *
 * helper function to be used by mem_cgroup_iter
 */
static struct mem_cgroup *__mem_cgroup_iter_next(struct mem_cgroup *root,
                struct mem_cgroup *last_visited, mem_cgroup_iter_filter cond)
{
        struct cgroup_subsys_state *prev_css, *next_css;

        prev_css = last_visited ? &last_visited->css : NULL;
skip_node:
        next_css = css_next_descendant_pre(prev_css, &root->css);

        /*
         * Even if we found a group we have to make sure it is
         * alive. css && !memcg means that the groups should be
         * skipped and we should continue the tree walk.
         * last_visited css is safe to use because it is
         * protected by css_get and the tree walk is rcu safe.
         */
        if (next_css) {
                struct mem_cgroup *mem = mem_cgroup_from_css(next_css);

                switch (mem_cgroup_filter(mem, root, cond)) {
                case SKIP:
                        prev_css = next_css;
                        goto skip_node;
                case SKIP_TREE:
                        if (mem == root)
                                return NULL;
                        /*
                         * css_rightmost_descendant is not an optimal way to
                         * skip through a subtree (especially for imbalanced
                         * trees leaning to right) but that's what we have right
                         * now. More effective solution would be traversing
                         * right-up for first non-NULL without calling
                         * css_next_descendant_pre afterwards.
                         */
                        prev_css = css_rightmost_descendant(next_css);
                        goto skip_node;
                case VISIT:
                        if (css_tryget(&mem->css))
                                return mem;
                        else {
                                prev_css = next_css;
                                goto skip_node;
                        }
                        break;
                }
        }

        return NULL;
}

static void mem_cgroup_iter_invalidate(struct mem_cgroup *root)
{
        /*
         * When a group in the hierarchy below root is destroyed, the
         * hierarchy iterator can no longer be trusted since it might
         * have pointed to the destroyed group.  Invalidate it.
         */
        atomic_inc(&root->dead_count);
}

static struct mem_cgroup *
mem_cgroup_iter_load(struct mem_cgroup_reclaim_iter *iter,
                     struct mem_cgroup *root,
                     int *sequence)
{
        struct mem_cgroup *position = NULL;
        /*
         * A cgroup destruction happens in two stages: offlining and
         * release.  They are separated by a RCU grace period.
         *
         * If the iterator is valid, we may still race with an
         * offlining.  The RCU lock ensures the object won't be
         * released, tryget will fail if we lost the race.
         */
        *sequence = atomic_read(&root->dead_count);
        if (iter->last_dead_count == *sequence) {
                smp_rmb();
                position = iter->last_visited;
                if (position && !css_tryget(&position->css))
                        position = NULL;
        }
        return position;
}

static void mem_cgroup_iter_update(struct mem_cgroup_reclaim_iter *iter,
                                   struct mem_cgroup *last_visited,
                                   struct mem_cgroup *new_position,
                                   int sequence)
{
        if (last_visited)
                css_put(&last_visited->css);
        /*
         * We store the sequence count from the time @last_visited was
         * loaded successfully instead of rereading it here so that we
         * don't lose destruction events in between.  We could have
         * raced with the destruction of @new_position after all.
         */
        iter->last_visited = new_position;
        smp_wmb();
        iter->last_dead_count = sequence;
}

/**
 * mem_cgroup_iter - iterate over memory cgroup hierarchy
 * @root: hierarchy root
 * @prev: previously returned memcg, NULL on first invocation
 * @reclaim: cookie for shared reclaim walks, NULL for full walks
 * @cond: filter for visited nodes, NULL for no filter
 *
 * Returns references to children of the hierarchy below @root, or
 * @root itself, or %NULL after a full round-trip.
 *
 * Caller must pass the return value in @prev on subsequent
 * invocations for reference counting, or use mem_cgroup_iter_break()
 * to cancel a hierarchy walk before the round-trip is complete.
 *
 * Reclaimers can specify a zone and a priority level in @reclaim to
 * divide up the memcgs in the hierarchy among all concurrent
 * reclaimers operating on the same zone and priority.
 */
struct mem_cgroup *mem_cgroup_iter_cond(struct mem_cgroup *root,
                                   struct mem_cgroup *prev,
                                   struct mem_cgroup_reclaim_cookie *reclaim,
                                   mem_cgroup_iter_filter cond)
{
        struct mem_cgroup *memcg = NULL;
        struct mem_cgroup *last_visited = NULL;

        if (mem_cgroup_disabled()) {
                /* first call must return non-NULL, second return NULL */
                return (struct mem_cgroup *)(unsigned long)!prev;
        }

        if (!root)
                root = root_mem_cgroup;

        if (prev && !reclaim)
                last_visited = prev;

        if (!root->use_hierarchy && root != root_mem_cgroup) {
                if (prev)
                        goto out_css_put;
                if (mem_cgroup_filter(root, root, cond) == VISIT)
                        return root;
                return NULL;
        }

        rcu_read_lock();
        while (!memcg) {
                struct mem_cgroup_reclaim_iter *uninitialized_var(iter);
                int uninitialized_var(seq);

                if (reclaim) {
                        int nid = zone_to_nid(reclaim->zone);
                        int zid = zone_idx(reclaim->zone);
                        struct mem_cgroup_per_zone *mz;

                        mz = mem_cgroup_zoneinfo(root, nid, zid);
                        iter = &mz->reclaim_iter[reclaim->priority];
                        if (prev && reclaim->generation != iter->generation) {
                                iter->last_visited = NULL;
                                goto out_unlock;
                        }

                        last_visited = mem_cgroup_iter_load(iter, root, &seq);
                }

                memcg = __mem_cgroup_iter_next(root, last_visited, cond);

                if (reclaim) {
                        mem_cgroup_iter_update(iter, last_visited, memcg, seq);

                        if (!memcg)
                                iter->generation++;
                        else if (!prev && memcg)
                                reclaim->generation = iter->generation;
                }

                /*
                 * We have finished the whole tree walk or no group has been
                 * visited because filter told us to skip the root node.
                 */
                if (!memcg && (prev || (cond && !last_visited)))
                        goto out_unlock;
        }
out_unlock:
        rcu_read_unlock();
out_css_put:
        if (prev && prev != root)
                css_put(&prev->css);

        return memcg;
}

/**
 * mem_cgroup_iter_break - abort a hierarchy walk prematurely
 * @root: hierarchy root
 * @prev: last visited hierarchy member as returned by mem_cgroup_iter()
 */
void mem_cgroup_iter_break(struct mem_cgroup *root,
                           struct mem_cgroup *prev)
{
        if (!root)
                root = root_mem_cgroup;
        if (prev && prev != root)
                css_put(&prev->css);
}

/*
 * Iteration constructs for visiting all cgroups (under a tree).  If
 * loops are exited prematurely (break), mem_cgroup_iter_break() must
 * be used for reference counting.
 */
#define for_each_mem_cgroup_tree(iter, root)            \
        for (iter = mem_cgroup_iter(root, NULL, NULL);  \
             iter != NULL;                              \
             iter = mem_cgroup_iter(root, iter, NULL))

#define for_each_mem_cgroup(iter)                       \
        for (iter = mem_cgroup_iter(NULL, NULL, NULL);  \
             iter != NULL;                              \
             iter = mem_cgroup_iter(NULL, iter, NULL))

void __mem_cgroup_count_vm_event(struct mm_struct *mm, enum vm_event_item idx)
{
        struct mem_cgroup *memcg;

        rcu_read_lock();
        memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
        if (unlikely(!memcg))
                goto out;

        switch (idx) {
        case PGFAULT:
                this_cpu_inc(memcg->stat->events[MEM_CGROUP_EVENTS_PGFAULT]);
                break;
        case PGMAJFAULT:
                this_cpu_inc(memcg->stat->events[MEM_CGROUP_EVENTS_PGMAJFAULT]);
                break;
        default:
                BUG();
        }
out:
        rcu_read_unlock();
}
EXPORT_SYMBOL(__mem_cgroup_count_vm_event);

/**
 * mem_cgroup_zone_lruvec - get the lru list vector for a zone and memcg
 * @zone: zone of the wanted lruvec
 * @memcg: memcg of the wanted lruvec
 *
 * Returns the lru list vector holding pages for the given @zone and
 * @mem.  This can be the global zone lruvec, if the memory controller
 * is disabled.
 */
struct lruvec *mem_cgroup_zone_lruvec(struct zone *zone,
                                      struct mem_cgroup *memcg)
{
        struct mem_cgroup_per_zone *mz;
        struct lruvec *lruvec;

        if (mem_cgroup_disabled()) {
                lruvec = &zone->lruvec;
                goto out;
        }

        mz = mem_cgroup_zoneinfo(memcg, zone_to_nid(zone), zone_idx(zone));
        lruvec = &mz->lruvec;
out:
        /*
         * Since a node can be onlined after the mem_cgroup was created,
         * we have to be prepared to initialize lruvec->zone here;
         * and if offlined then reonlined, we need to reinitialize it.
         */
        if (unlikely(lruvec->zone != zone))
                lruvec->zone = zone;
        return lruvec;
}

/*
 * Following LRU functions are allowed to be used without PCG_LOCK.
 * Operations are called by routine of global LRU independently from memcg.
 * What we have to take care of here is validness of pc->mem_cgroup.
 *
 * Changes to pc->mem_cgroup happens when
 * 1. charge
 * 2. moving account
 * In typical case, "charge" is done before add-to-lru. Exception is SwapCache.
 * It is added to LRU before charge.
 * If PCG_USED bit is not set, page_cgroup is not added to this private LRU.
 * When moving account, the page is not on LRU. It's isolated.
 */

/**
 * mem_cgroup_page_lruvec - return lruvec for adding an lru page
 * @page: the page
 * @zone: zone of the page
 */
struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct zone *zone)
{
        struct mem_cgroup_per_zone *mz;
        struct mem_cgroup *memcg;
        struct page_cgroup *pc;
        struct lruvec *lruvec;

        if (mem_cgroup_disabled()) {
                lruvec = &zone->lruvec;
                goto out;
        }

        pc = lookup_page_cgroup(page);
        memcg = pc->mem_cgroup;

        /*
         * Surreptitiously switch any uncharged offlist page to root:
         * an uncharged page off lru does nothing to secure
         * its former mem_cgroup from sudden removal.
         *
         * Our caller holds lru_lock, and PageCgroupUsed is updated
         * under page_cgroup lock: between them, they make all uses
         * of pc->mem_cgroup safe.
         */
        if (!PageLRU(page) && !PageCgroupUsed(pc) && memcg != root_mem_cgroup)
                pc->mem_cgroup = memcg = root_mem_cgroup;

        mz = page_cgroup_zoneinfo(memcg, page);
        lruvec = &mz->lruvec;
out:
        /*
         * Since a node can be onlined after the mem_cgroup was created,
         * we have to be prepared to initialize lruvec->zone here;
         * and if offlined then reonlined, we need to reinitialize it.
         */
        if (unlikely(lruvec->zone != zone))
                lruvec->zone = zone;
        return lruvec;
}

/**
 * mem_cgroup_update_lru_size - account for adding or removing an lru page
 * @lruvec: mem_cgroup per zone lru vector
 * @lru: index of lru list the page is sitting on
 * @nr_pages: positive when adding or negative when removing
 *
 * This function must be called when a page is added to or removed from an
 * lru list.
 */
void mem_cgroup_update_lru_size(struct lruvec *lruvec, enum lru_list lru,
                                int nr_pages)
{
        struct mem_cgroup_per_zone *mz;
        unsigned long *lru_size;

        if (mem_cgroup_disabled())
                return;

        mz = container_of(lruvec, struct mem_cgroup_per_zone, lruvec);
        lru_size = mz->lru_size + lru;
        *lru_size += nr_pages;
        VM_BUG_ON((long)(*lru_size) < 0);
}

/*
 * Checks whether given mem is same or in the root_mem_cgroup's
 * hierarchy subtree
 */
bool __mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
                                  struct mem_cgroup *memcg)
{
        if (root_memcg == memcg)
                return true;
        if (!root_memcg->use_hierarchy || !memcg)
                return false;
        return css_is_ancestor(&memcg->css, &root_memcg->css);
}

static bool mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
                                       struct mem_cgroup *memcg)
{
        bool ret;

        rcu_read_lock();
        ret = __mem_cgroup_same_or_subtree(root_memcg, memcg);
        rcu_read_unlock();
        return ret;
}

bool task_in_mem_cgroup(struct task_struct *task,
                        const struct mem_cgroup *memcg)
{
        struct mem_cgroup *curr = NULL;
        struct task_struct *p;
        bool ret;

        p = find_lock_task_mm(task);
        if (p) {
                curr = try_get_mem_cgroup_from_mm(p->mm);
                task_unlock(p);
        } else {
                /*
                 * All threads may have already detached their mm's, but the oom
                 * killer still needs to detect if they have already been oom
                 * killed to prevent needlessly killing additional tasks.
                 */
                rcu_read_lock();
                curr = mem_cgroup_from_task(task);
                if (curr)
                        css_get(&curr->css);
                rcu_read_unlock();
        }
        if (!curr)
                return false;
        /*
         * We should check use_hierarchy of "memcg" not "curr". Because checking
         * use_hierarchy of "curr" here make this function true if hierarchy is
         * enabled in "curr" and "curr" is a child of "memcg" in *cgroup*
         * hierarchy(even if use_hierarchy is disabled in "memcg").
         */
        ret = mem_cgroup_same_or_subtree(memcg, curr);
        css_put(&curr->css);
        return ret;
}

int mem_cgroup_inactive_anon_is_low(struct lruvec *lruvec)
{
        unsigned long inactive_ratio;
        unsigned long inactive;
        unsigned long active;
        unsigned long gb;

        inactive = mem_cgroup_get_lru_size(lruvec, LRU_INACTIVE_ANON);
        active = mem_cgroup_get_lru_size(lruvec, LRU_ACTIVE_ANON);

        gb = (inactive + active) >> (30 - PAGE_SHIFT);
        if (gb)
                inactive_ratio = int_sqrt(10 * gb);
        else
                inactive_ratio = 1;

        return inactive * inactive_ratio < active;
}

#define mem_cgroup_from_res_counter(counter, member)    \
        container_of(counter, struct mem_cgroup, member)

/**
 * mem_cgroup_margin - calculate chargeable space of a memory cgroup
 * @memcg: the memory cgroup
 *
 * Returns the maximum amount of memory @mem can be charged with, in
 * pages.
 */
static unsigned long mem_cgroup_margin(struct mem_cgroup *memcg)
{
        unsigned long long margin;

        margin = res_counter_margin(&memcg->res);
        if (do_swap_account)
                margin = min(margin, res_counter_margin(&memcg->memsw));
        return margin >> PAGE_SHIFT;
}

int mem_cgroup_swappiness(struct mem_cgroup *memcg)
{
        /* root ? */
        if (!css_parent(&memcg->css))
                return vm_swappiness;

        return memcg->swappiness;
}

/*
 * memcg->moving_account is used for checking possibility that some thread is
 * calling move_account(). When a thread on CPU-A starts moving pages under
 * a memcg, other threads should check memcg->moving_account under
 * rcu_read_lock(), like this:
 *
 *         CPU-A                                    CPU-B
 *                                              rcu_read_lock()
 *         memcg->moving_account+1              if (memcg->mocing_account)
 *                                                   take heavy locks.
 *         synchronize_rcu()                    update something.
 *                                              rcu_read_unlock()
 *         start move here.
 */

/* for quick checking without looking up memcg */
atomic_t memcg_moving __read_mostly;

static void mem_cgroup_start_move(struct mem_cgroup *memcg)
{
        atomic_inc(&memcg_moving);
        atomic_inc(&memcg->moving_account);
        synchronize_rcu();
}

static void mem_cgroup_end_move(struct mem_cgroup *memcg)
{
        /*
         * Now, mem_cgroup_clear_mc() may call this function with NULL.
         * We check NULL in callee rather than caller.
         */
        if (memcg) {
                atomic_dec(&memcg_moving);
                atomic_dec(&memcg->moving_account);
        }
}

/*
 * 2 routines for checking "mem" is under move_account() or not.
 *
 * mem_cgroup_stolen() -  checking whether a cgroup is mc.from or not. This
 *                        is used for avoiding races in accounting.  If true,
 *                        pc->mem_cgroup may be overwritten.
 *
 * mem_cgroup_under_move() - checking a cgroup is mc.from or mc.to or
 *                        under hierarchy of moving cgroups. This is for
 *                        waiting at hith-memory prressure caused by "move".
 */

static bool mem_cgroup_stolen(struct mem_cgroup *memcg)
{
        VM_BUG_ON(!rcu_read_lock_held());
        return atomic_read(&memcg->moving_account) > 0;
}

static bool mem_cgroup_under_move(struct mem_cgroup *memcg)
{
        struct mem_cgroup *from;
        struct mem_cgroup *to;
        bool ret = false;
        /*
         * Unlike task_move routines, we access mc.to, mc.from not under
         * mutual exclusion by cgroup_mutex. Here, we take spinlock instead.
         */
        spin_lock(&mc.lock);
        from = mc.from;
        to = mc.to;
        if (!from)
                goto unlock;

        ret = mem_cgroup_same_or_subtree(memcg, from)
                || mem_cgroup_same_or_subtree(memcg, to);
unlock:
        spin_unlock(&mc.lock);
        return ret;
}

static bool mem_cgroup_wait_acct_move(struct mem_cgroup *memcg)
{
        if (mc.moving_task && current != mc.moving_task) {
                if (mem_cgroup_under_move(memcg)) {
                        DEFINE_WAIT(wait);
                        prepare_to_wait(&mc.waitq, &wait, TASK_INTERRUPTIBLE);
                        /* moving charge context might have finished. */
                        if (mc.moving_task)
                                schedule();
                        finish_wait(&mc.waitq, &wait);
                        return true;
                }
        }
        return false;
}

/*
 * Take this lock when
 * - a code tries to modify page's memcg while it's USED.
 * - a code tries to modify page state accounting in a memcg.
 * see mem_cgroup_stolen(), too.
 */
static void move_lock_mem_cgroup(struct mem_cgroup *memcg,
                                  unsigned long *flags)
{
        spin_lock_irqsave(&memcg->move_lock, *flags);
}

static void move_unlock_mem_cgroup(struct mem_cgroup *memcg,
                                unsigned long *flags)
{
        spin_unlock_irqrestore(&memcg->move_lock, *flags);
}

#define K(x) ((x) << (PAGE_SHIFT-10))
/**
 * mem_cgroup_print_oom_info: Print OOM information relevant to memory controller.
 * @memcg: The memory cgroup that went over limit
 * @p: Task that is going to be killed
 *
 * NOTE: @memcg and @p's mem_cgroup can be different when hierarchy is
 * enabled
 */
void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p)
{
        struct cgroup *task_cgrp;
        struct cgroup *mem_cgrp;
        /*
         * Need a buffer in BSS, can't rely on allocations. The code relies
         * on the assumption that OOM is serialized for memory controller.
         * If this assumption is broken, revisit this code.
         */
        static char memcg_name[PATH_MAX];
        int ret;
        struct mem_cgroup *iter;
        unsigned int i;

        if (!p)
                return;

        rcu_read_lock();

        mem_cgrp = memcg->css.cgroup;
        task_cgrp = task_cgroup(p, mem_cgroup_subsys_id);

        ret = cgroup_path(task_cgrp, memcg_name, PATH_MAX);
        if (ret < 0) {
                /*
                 * Unfortunately, we are unable to convert to a useful name
                 * But we'll still print out the usage information
                 */
                rcu_read_unlock();
                goto done;
        }
        rcu_read_unlock();

        pr_info("Task in %s killed", memcg_name);

        rcu_read_lock();
        ret = cgroup_path(mem_cgrp, memcg_name, PATH_MAX);
        if (ret < 0) {
                rcu_read_unlock();
                goto done;
        }
        rcu_read_unlock();

        /*
         * Continues from above, so we don't need an KERN_ level
         */
        pr_cont(" as a result of limit of %s\n", memcg_name);
done:

        pr_info("memory: usage %llukB, limit %llukB, failcnt %llu\n",
                res_counter_read_u64(&memcg->res, RES_USAGE) >> 10,
                res_counter_read_u64(&memcg->res, RES_LIMIT) >> 10,
                res_counter_read_u64(&memcg->res, RES_FAILCNT));
        pr_info("memory+swap: usage %llukB, limit %llukB, failcnt %llu\n",
                res_counter_read_u64(&memcg->memsw, RES_USAGE) >> 10,
                res_counter_read_u64(&memcg->memsw, RES_LIMIT) >> 10,
                res_counter_read_u64(&memcg->memsw, RES_FAILCNT));
        pr_info("kmem: usage %llukB, limit %llukB, failcnt %llu\n",
                res_counter_read_u64(&memcg->kmem, RES_USAGE) >> 10,
                res_counter_read_u64(&memcg->kmem, RES_LIMIT) >> 10,
                res_counter_read_u64(&memcg->kmem, RES_FAILCNT));

        for_each_mem_cgroup_tree(iter, memcg) {
                pr_info("Memory cgroup stats");

                rcu_read_lock();
                ret = cgroup_path(iter->css.cgroup, memcg_name, PATH_MAX);
                if (!ret)
                        pr_cont(" for %s", memcg_name);
                rcu_read_unlock();
                pr_cont(":");

                for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) {
                        if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account)
                                continue;
                        pr_cont(" %s:%ldKB", mem_cgroup_stat_names[i],
                                K(mem_cgroup_read_stat(iter, i)));
                }

                for (i = 0; i < NR_LRU_LISTS; i++)
                        pr_cont(" %s:%luKB", mem_cgroup_lru_names[i],
                                K(mem_cgroup_nr_lru_pages(iter, BIT(i))));

                pr_cont("\n");
        }
}

/*
 * This function returns the number of memcg under hierarchy tree. Returns
 * 1(self count) if no children.
 */
static int mem_cgroup_count_children(struct mem_cgroup *memcg)
{
        int num = 0;
        struct mem_cgroup *iter;

        for_each_mem_cgroup_tree(iter, memcg)
                num++;
        return num;
}

/*
 * Return the memory (and swap, if configured) limit for a memcg.
 */
static u64 mem_cgroup_get_limit(struct mem_cgroup *memcg)
{
        u64 limit;

        limit = res_counter_read_u64(&memcg->res, RES_LIMIT);

        /*
         * Do not consider swap space if we cannot swap due to swappiness
         */
        if (mem_cgroup_swappiness(memcg)) {
                u64 memsw;

                limit += total_swap_pages << PAGE_SHIFT;
                memsw = res_counter_read_u64(&memcg->memsw, RES_LIMIT);

                /*
                 * If memsw is finite and limits the amount of swap space
                 * available to this memcg, return that limit.
                 */
                limit = min(limit, memsw);
        }

        return limit;
}

static void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
                                     int order)
{
        struct mem_cgroup *iter;
        unsigned long chosen_points = 0;
        unsigned long totalpages;
        unsigned int points = 0;
        struct task_struct *chosen = NULL;

        /*
         * If current has a pending SIGKILL or is exiting, then automatically
         * select it.  The goal is to allow it to allocate so that it may
         * quickly exit and free its memory.
         */
        if (fatal_signal_pending(current) || current->flags & PF_EXITING) {
                set_thread_flag(TIF_MEMDIE);
                return;
        }

        check_panic_on_oom(CONSTRAINT_MEMCG, gfp_mask, order, NULL);
        totalpages = mem_cgroup_get_limit(memcg) >> PAGE_SHIFT ? : 1;
        for_each_mem_cgroup_tree(iter, memcg) {
                struct css_task_iter it;
                struct task_struct *task;

                css_task_iter_start(&iter->css, &it);
                while ((task = css_task_iter_next(&it))) {
                        switch (oom_scan_process_thread(task, totalpages, NULL,
                                                        false)) {
                        case OOM_SCAN_SELECT:
                                if (chosen)
                                        put_task_struct(chosen);
                                chosen = task;
                                chosen_points = ULONG_MAX;
                                get_task_struct(chosen);
                                /* fall through */
                        case OOM_SCAN_CONTINUE:
                                continue;
                        case OOM_SCAN_ABORT:
                                css_task_iter_end(&it);
                                mem_cgroup_iter_break(memcg, iter);
                                if (chosen)
                                        put_task_struct(chosen);
                                return;
                        case OOM_SCAN_OK:
                                break;
                        };
                        points = oom_badness(task, memcg, NULL, totalpages);
                        if (points > chosen_points) {
                                if (chosen)
                                        put_task_struct(chosen);
                                chosen = task;
                                chosen_points = points;
                                get_task_struct(chosen);
                        }
                }
                css_task_iter_end(&it);
        }

        if (!chosen)
                return;
        points = chosen_points * 1000 / totalpages;
        oom_kill_process(chosen, gfp_mask, order, points, totalpages, memcg,
                         NULL, "Memory cgroup out of memory");
}

static unsigned long mem_cgroup_reclaim(struct mem_cgroup *memcg,
                                        gfp_t gfp_mask,
                                        unsigned long flags)
{
        unsigned long total = 0;
        bool noswap = false;
        int loop;

        if (flags & MEM_CGROUP_RECLAIM_NOSWAP)
                noswap = true;
        if (!(flags & MEM_CGROUP_RECLAIM_SHRINK) && memcg->memsw_is_minimum)
                noswap = true;

        for (loop = 0; loop < MEM_CGROUP_MAX_RECLAIM_LOOPS; loop++) {
                if (loop)
                        drain_all_stock_async(memcg);
                total += try_to_free_mem_cgroup_pages(memcg, gfp_mask, noswap);
                /*
                 * Allow limit shrinkers, which are triggered directly
                 * by userspace, to catch signals and stop reclaim
                 * after minimal progress, regardless of the margin.
                 */
                if (total && (flags & MEM_CGROUP_RECLAIM_SHRINK))
                        break;
                if (mem_cgroup_margin(memcg))
                        break;
                /*
                 * If nothing was reclaimed after two attempts, there
                 * may be no reclaimable pages in this hierarchy.
                 */
                if (loop && !total)
                        break;
        }
        return total;
}

#if MAX_NUMNODES > 1
/**
 * test_mem_cgroup_node_reclaimable
 * @memcg: the target memcg
 * @nid: the node ID to be checked.
 * @noswap : specify true here if the user wants flle only information.
 *
 * This function returns whether the specified memcg contains any
 * reclaimable pages on a node. Returns true if there are any reclaimable
 * pages in the node.
 */
static bool test_mem_cgroup_node_reclaimable(struct mem_cgroup *memcg,
                int nid, bool noswap)
{
        if (mem_cgroup_node_nr_lru_pages(memcg, nid, LRU_ALL_FILE))
                return true;
        if (noswap || !total_swap_pages)
                return false;
        if (mem_cgroup_node_nr_lru_pages(memcg, nid, LRU_ALL_ANON))
                return true;
        return false;

}

/*
 * Always updating the nodemask is not very good - even if we have an empty
 * list or the wrong list here, we can start from some node and traverse all
 * nodes based on the zonelist. So update the list loosely once per 10 secs.
 *
 */
static void mem_cgroup_may_update_nodemask(struct mem_cgroup *memcg)
{
        int nid;
        /*
         * numainfo_events > 0 means there was at least NUMAINFO_EVENTS_TARGET
         * pagein/pageout changes since the last update.
         */
        if (!atomic_read(&memcg->numainfo_events))
                return;
        if (atomic_inc_return(&memcg->numainfo_updating) > 1)
                return;

        /* make a nodemask where this memcg uses memory from */
        memcg->scan_nodes = node_states[N_MEMORY];

        for_each_node_mask(nid, node_states[N_MEMORY]) {

                if (!test_mem_cgroup_node_reclaimable(memcg, nid, false))
                        node_clear(nid, memcg->scan_nodes);
        }

        atomic_set(&memcg->numainfo_events, 0);
        atomic_set(&memcg->numainfo_updating, 0);
}

/*
 * Selecting a node where we start reclaim from. Because what we need is just
 * reducing usage counter, start from anywhere is O,K. Considering
 * memory reclaim from current node, there are pros. and cons.
 *
 * Freeing memory from current node means freeing memory from a node which
 * we'll use or we've used. So, it may make LRU bad. And if several threads
 * hit limits, it will see a contention on a node. But freeing from remote
 * node means more costs for memory reclaim because of memory latency.
 *
 * Now, we use round-robin. Better algorithm is welcomed.
 */
int mem_cgroup_select_victim_node(struct mem_cgroup *memcg)
{
        int node;

        mem_cgroup_may_update_nodemask(memcg);
        node = memcg->last_scanned_node;

        node = next_node(node, memcg->scan_nodes);
        if (node == MAX_NUMNODES)
                node = first_node(memcg->scan_nodes);
        /*
         * We call this when we hit limit, not when pages are added to LRU.
         * No LRU may hold pages because all pages are UNEVICTABLE or
         * memcg is too small and all pages are not on LRU. In that case,
         * we use curret node.
         */
        if (unlikely(node == MAX_NUMNODES))
                node = numa_node_id();

        memcg->last_scanned_node = node;
        return node;
}

#else
int mem_cgroup_select_victim_node(struct mem_cgroup *memcg)
{
        return 0;
}

#endif

/*
 * A group is eligible for the soft limit reclaim under the given root
 * hierarchy if
 *      a) it is over its soft limit
 *      b) any parent up the hierarchy is over its soft limit
 *
 * If the given group doesn't have any children over the limit then it
 * doesn't make any sense to iterate its subtree.
 */
enum mem_cgroup_filter_t
mem_cgroup_soft_reclaim_eligible(struct mem_cgroup *memcg,
                struct mem_cgroup *root)
{
        struct mem_cgroup *parent;

        if (!memcg)
                memcg = root_mem_cgroup;
        parent = memcg;

        if (res_counter_soft_limit_excess(&memcg->res))
                return VISIT;

        /*
         * If any parent up to the root in the hierarchy is over its soft limit
         * then we have to obey and reclaim from this group as well.
         */
        while((parent = parent_mem_cgroup(parent))) {
                if (res_counter_soft_limit_excess(&parent->res))
                        return VISIT;
                if (parent == root)
                        break;
        }

        if (!atomic_read(&memcg->children_in_excess))
                return SKIP_TREE;
        return SKIP;
}

/*
 * Check OOM-Killer is already running under our hierarchy.
 * If someone is running, return false.
 * Has to be called with memcg_oom_lock
 */
static bool mem_cgroup_oom_lock(struct mem_cgroup *memcg)
{
        struct mem_cgroup *iter, *failed = NULL;

        for_each_mem_cgroup_tree(iter, memcg) {
                if (iter->oom_lock) {
                        /*
                         * this subtree of our hierarchy is already locked
                         * so we cannot give a lock.
                         */
                        failed = iter;
                        mem_cgroup_iter_break(memcg, iter);
                        break;
                } else
                        iter->oom_lock = true;
        }

        if (!failed)
                return true;

        /*
         * OK, we failed to lock the whole subtree so we have to clean up
         * what we set up to the failing subtree
         */
        for_each_mem_cgroup_tree(iter, memcg) {
                if (iter == failed) {
                        mem_cgroup_iter_break(memcg, iter);
                        break;
                }
                iter->oom_lock = false;
        }
        return false;
}

/*
 * Has to be called with memcg_oom_lock
 */
static int mem_cgroup_oom_unlock(struct mem_cgroup *memcg)
{
        struct mem_cgroup *iter;

        for_each_mem_cgroup_tree(iter, memcg)
                iter->oom_lock = false;
        return 0;
}

static void mem_cgroup_mark_under_oom(struct mem_cgroup *memcg)
{
        struct mem_cgroup *iter;

        for_each_mem_cgroup_tree(iter, memcg)
                atomic_inc(&iter->under_oom);
}

static void mem_cgroup_unmark_under_oom(struct mem_cgroup *memcg)
{
        struct mem_cgroup *iter;

        /*
         * When a new child is created while the hierarchy is under oom,
         * mem_cgroup_oom_lock() may not be called. We have to use
         * atomic_add_unless() here.
         */
        for_each_mem_cgroup_tree(iter, memcg)
                atomic_add_unless(&iter->under_oom, -1, 0);
}

static DEFINE_SPINLOCK(memcg_oom_lock);
static DECLARE_WAIT_QUEUE_HEAD(memcg_oom_waitq);

struct oom_wait_info {
        struct mem_cgroup *memcg;
        wait_queue_t    wait;
};

static int memcg_oom_wake_function(wait_queue_t *wait,
        unsigned mode, int sync, void *arg)
{
        struct mem_cgroup *wake_memcg = (struct mem_cgroup *)arg;
        struct mem_cgroup *oom_wait_memcg;
        struct oom_wait_info *oom_wait_info;

        oom_wait_info = container_of(wait, struct oom_wait_info, wait);
        oom_wait_memcg = oom_wait_info->memcg;

        /*
         * Both of oom_wait_info->memcg and wake_memcg are stable under us.
         * Then we can use css_is_ancestor without taking care of RCU.
         */
        if (!mem_cgroup_same_or_subtree(oom_wait_memcg, wake_memcg)
                && !mem_cgroup_same_or_subtree(wake_memcg, oom_wait_memcg))
                return 0;
        return autoremove_wake_function(wait, mode, sync, arg);
}

static void memcg_wakeup_oom(struct mem_cgroup *memcg)
{
        /* for filtering, pass "memcg" as argument. */
        __wake_up(&memcg_oom_waitq, TASK_NORMAL, 0, memcg);
}

static void memcg_oom_recover(struct mem_cgroup *memcg)
{
        if (memcg && atomic_read(&memcg->under_oom))
                memcg_wakeup_oom(memcg);
}

/*
 * try to call OOM killer. returns false if we should exit memory-reclaim loop.
 */
static bool mem_cgroup_handle_oom(struct mem_cgroup *memcg, gfp_t mask,
                                  int order)
{
        struct oom_wait_info owait;
        bool locked, need_to_kill;

        owait.memcg = memcg;
        owait.wait.flags = 0;
        owait.wait.func = memcg_oom_wake_function;
        owait.wait.private = current;
        INIT_LIST_HEAD(&owait.wait.task_list);
        need_to_kill = true;
        mem_cgroup_mark_under_oom(memcg);

        /* At first, try to OOM lock hierarchy under memcg.*/
        spin_lock(&memcg_oom_lock);
        locked = mem_cgroup_oom_lock(memcg);
        /*
         * Even if signal_pending(), we can't quit charge() loop without
         * accounting. So, UNINTERRUPTIBLE is appropriate. But SIGKILL
         * under OOM is always welcomed, use TASK_KILLABLE here.
         */
        prepare_to_wait(&memcg_oom_waitq, &owait.wait, TASK_KILLABLE);
        if (!locked || memcg->oom_kill_disable)
                need_to_kill = false;
        if (locked)
                mem_cgroup_oom_notify(memcg);
        spin_unlock(&memcg_oom_lock);

        if (need_to_kill) {
                finish_wait(&memcg_oom_waitq, &owait.wait);
                mem_cgroup_out_of_memory(memcg, mask, order);
        } else {
                schedule();
                finish_wait(&memcg_oom_waitq, &owait.wait);
        }
        spin_lock(&memcg_oom_lock);
        if (locked)
                mem_cgroup_oom_unlock(memcg);
        memcg_wakeup_oom(memcg);
        spin_unlock(&memcg_oom_lock);

        mem_cgroup_unmark_under_oom(memcg);

        if (test_thread_flag(TIF_MEMDIE) || fatal_signal_pending(current))
                return false;
        /* Give chance to dying process */
        schedule_timeout_uninterruptible(1);
        return true;
}

/*
 * Currently used to update mapped file statistics, but the routine can be
 * generalized to update other statistics as well.
 *
 * Notes: Race condition
 *
 * We usually use page_cgroup_lock() for accessing page_cgroup member but
 * it tends to be costly. But considering some conditions, we doesn't need
 * to do so _always_.
 *
 * Considering "charge", lock_page_cgroup() is not required because all
 * file-stat operations happen after a page is attached to radix-tree. There
 * are no race with "charge".
 *
 * Considering "uncharge", we know that memcg doesn't clear pc->mem_cgroup
 * at "uncharge" intentionally. So, we always see valid pc->mem_cgroup even
 * if there are race with "uncharge". Statistics itself is properly handled
 * by flags.
 *
 * Considering "move", this is an only case we see a race. To make the race
 * small, we check mm->moving_account and detect there are possibility of race
 * If there is, we take a lock.
 */

void __mem_cgroup_begin_update_page_stat(struct page *page,
                                bool *locked, unsigned long *flags)
{
        struct mem_cgroup *memcg;
        struct page_cgroup *pc;

        pc = lookup_page_cgroup(page);
again:
        memcg = pc->mem_cgroup;
        if (unlikely(!memcg || !PageCgroupUsed(pc)))
                return;
        /*
         * If this memory cgroup is not under account moving, we don't
         * need to take move_lock_mem_cgroup(). Because we already hold
         * rcu_read_lock(), any calls to move_account will be delayed until
         * rcu_read_unlock() if mem_cgroup_stolen() == true.
         */
        if (!mem_cgroup_stolen(memcg))
                return;

        move_lock_mem_cgroup(memcg, flags);
        if (memcg != pc->mem_cgroup || !PageCgroupUsed(pc)) {
                move_unlock_mem_cgroup(memcg, flags);
                goto again;
        }
        *locked = true;
}

void __mem_cgroup_end_update_page_stat(struct page *page, unsigned long *flags)
{
        struct page_cgroup *pc = lookup_page_cgroup(page);

        /*
         * It's guaranteed that pc->mem_cgroup never changes while
         * lock is held because a routine modifies pc->mem_cgroup
         * should take move_lock_mem_cgroup().
         */
        move_unlock_mem_cgroup(pc->mem_cgroup, flags);
}

void mem_cgroup_update_page_stat(struct page *page,
                                 enum mem_cgroup_page_stat_item idx, int val)
{
        struct mem_cgroup *memcg;
        struct page_cgroup *pc = lookup_page_cgroup(page);
        unsigned long uninitialized_var(flags);

        if (mem_cgroup_disabled())
                return;

        memcg = pc->mem_cgroup;
        if (unlikely(!memcg || !PageCgroupUsed(pc)))
                return;

        switch (idx) {
        case MEMCG_NR_FILE_MAPPED:
                idx = MEM_CGROUP_STAT_FILE_MAPPED;
                break;
        default:
                BUG();
        }

        this_cpu_add(memcg->stat->count[idx], val);
}

/*
 * size of first charge trial. "32" comes from vmscan.c's magic value.
 * TODO: maybe necessary to use big numbers in big irons.
 */
#define CHARGE_BATCH    32U
struct memcg_stock_pcp {
        struct mem_cgroup *cached; /* this never be root cgroup */
        unsigned int nr_pages;
        struct work_struct work;
        unsigned long flags;
#define FLUSHING_CACHED_CHARGE  0
};
static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock);
static DEFINE_MUTEX(percpu_charge_mutex);

/**
 * consume_stock: Try to consume stocked charge on this cpu.
 * @memcg: memcg to consume from.
 * @nr_pages: how many pages to charge.
 *
 * The charges will only happen if @memcg matches the current cpu's memcg
 * stock, and at least @nr_pages are available in that stock.  Failure to
 * service an allocation will refill the stock.
 *
 * returns true if successful, false otherwise.
 */
static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
{
        struct memcg_stock_pcp *stock;
        bool ret = true;

        if (nr_pages > CHARGE_BATCH)
                return false;

        stock = &get_cpu_var(memcg_stock);
        if (memcg == stock->cached && stock->nr_pages >= nr_pages)
                stock->nr_pages -= nr_pages;
        else /* need to call res_counter_charge */
                ret = false;
        put_cpu_var(memcg_stock);
        return ret;
}

/*
 * Returns stocks cached in percpu to res_counter and reset cached information.
 */
static void drain_stock(struct memcg_stock_pcp *stock)
{
        struct mem_cgroup *old = stock->cached;

        if (stock->nr_pages) {
                unsigned long bytes = stock->nr_pages * PAGE_SIZE;

                res_counter_uncharge(&old->res, bytes);
                if (do_swap_account)
                        res_counter_uncharge(&old->memsw, bytes);
                stock->nr_pages = 0;
        }
        stock->cached = NULL;
}

/*
 * This must be called under preempt disabled or must be called by
 * a thread which is pinned to local cpu.
 */
static void drain_local_stock(struct work_struct *dummy)
{
        struct memcg_stock_pcp *stock = &__get_cpu_var(memcg_stock);
        drain_stock(stock);
        clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags);
}

static void __init memcg_stock_init(void)
{
        int cpu;

        for_each_possible_cpu(cpu) {
                struct memcg_stock_pcp *stock =
                                        &per_cpu(memcg_stock, cpu);
                INIT_WORK(&stock->work, drain_local_stock);
        }
}

/*
 * Cache charges(val) which is from res_counter, to local per_cpu area.
 * This will be consumed by consume_stock() function, later.
 */
static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
{
        struct memcg_stock_pcp *stock = &get_cpu_var(memcg_stock);

        if (stock->cached != memcg) { /* reset if necessary */
                drain_stock(stock);
                stock->cached = memcg;
        }
        stock->nr_pages += nr_pages;
        put_cpu_var(memcg_stock);
}

/*
 * Drains all per-CPU charge caches for given root_memcg resp. subtree
 * of the hierarchy under it. sync flag says whether we should block
 * until the work is done.
 */
static void drain_all_stock(struct mem_cgroup *root_memcg, bool sync)
{
        int cpu, curcpu;

        /* Notify other cpus that system-wide "drain" is running */
        get_online_cpus();
        curcpu = get_cpu();
        for_each_online_cpu(cpu) {
                struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu);
                struct mem_cgroup *memcg;

                memcg = stock->cached;
                if (!memcg || !stock->nr_pages)
                        continue;
                if (!mem_cgroup_same_or_subtree(root_memcg, memcg))
                        continue;
                if (!test_and_set_bit(FLUSHING_CACHED_CHARGE, &stock->flags)) {
                        if (cpu == curcpu)
                                drain_local_stock(&stock->work);
                        else
                                schedule_work_on(cpu, &stock->work);
                }
        }
        put_cpu();

        if (!sync)
                goto out;

        for_each_online_cpu(cpu) {
                struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu);
                if (test_bit(FLUSHING_CACHED_CHARGE, &stock->flags))
                        flush_work(&stock->work);
        }
out:
        put_online_cpus();
}

/*
 * Tries to drain stocked charges in other cpus. This function is asynchronous
 * and just put a work per cpu for draining localy on each cpu. Caller can
 * expects some charges will be back to res_counter later but cannot wait for
 * it.
 */
static void drain_all_stock_async(struct mem_cgroup *root_memcg)
{
        /*
         * If someone calls draining, avoid adding more kworker runs.
         */
        if (!mutex_trylock(&percpu_charge_mutex))
                return;
        drain_all_stock(root_memcg, false);
        mutex_unlock(&percpu_charge_mutex);
}

/* This is a synchronous drain interface. */
static void drain_all_stock_sync(struct mem_cgroup *root_memcg)
{
        /* called when force_empty is called */
        mutex_lock(&percpu_charge_mutex);
        drain_all_stock(root_memcg, true);
        mutex_unlock(&percpu_charge_mutex);
}

/*
 * This function drains percpu counter value from DEAD cpu and
 * move it to local cpu. Note that this function can be preempted.
 */
static void mem_cgroup_drain_pcp_counter(struct mem_cgroup *memcg, int cpu)
{
        int i;

        spin_lock(&memcg->pcp_counter_lock);
        for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) {
                long x = per_cpu(memcg->stat->count[i], cpu);

                per_cpu(memcg->stat->count[i], cpu) = 0;
                memcg->nocpu_base.count[i] += x;
        }
        for (i = 0; i < MEM_CGROUP_EVENTS_NSTATS; i++) {
                unsigned long x = per_cpu(memcg->stat->events[i], cpu);

                per_cpu(memcg->stat->events[i], cpu) = 0;
                memcg->nocpu_base.events[i] += x;
        }
        spin_unlock(&memcg->pcp_counter_lock);
}

static int memcg_cpu_hotplug_callback(struct notifier_block *nb,
                                        unsigned long action,
                                        void *hcpu)
{
        int cpu = (unsigned long)hcpu;
        struct memcg_stock_pcp *stock;
        struct mem_cgroup *iter;

        if (action == CPU_ONLINE)
                return NOTIFY_OK;

        if (action != CPU_DEAD && action != CPU_DEAD_FROZEN)
                return NOTIFY_OK;

        for_each_mem_cgroup(iter)
                mem_cgroup_drain_pcp_counter(iter, cpu);

        stock = &per_cpu(memcg_stock, cpu);
        drain_stock(stock);
        return NOTIFY_OK;
}


/* See __mem_cgroup_try_charge() for details */
enum {
        CHARGE_OK,              /* success */
        CHARGE_RETRY,           /* need to retry but retry is not bad */
        CHARGE_NOMEM,           /* we can't do more. return -ENOMEM */
        CHARGE_WOULDBLOCK,      /* GFP_WAIT wasn't set and no enough res. */
        CHARGE_OOM_DIE,         /* the current is killed because of OOM */
};

static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
                                unsigned int nr_pages, unsigned int min_pages,
                                bool oom_check)
{
        unsigned long csize = nr_pages * PAGE_SIZE;
        struct mem_cgroup *mem_over_limit;
        struct res_counter *fail_res;
        unsigned long flags = 0;
        int ret;

        ret = res_counter_charge(&memcg->res, csize, &fail_res);

        if (likely(!ret)) {
                if (!do_swap_account)
                        return CHARGE_OK;
                ret = res_counter_charge(&memcg->memsw, csize, &fail_res);
                if (likely(!ret))
                        return CHARGE_OK;

                res_counter_uncharge(&memcg->res, csize);
                mem_over_limit = mem_cgroup_from_res_counter(fail_res, memsw);
                flags |= MEM_CGROUP_RECLAIM_NOSWAP;
        } else
                mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);
        /*
         * Never reclaim on behalf of optional batching, retry with a
         * single page instead.
         */
        if (nr_pages > min_pages)
                return CHARGE_RETRY;

        if (!(gfp_mask & __GFP_WAIT))
                return CHARGE_WOULDBLOCK;

        if (gfp_mask & __GFP_NORETRY)
                return CHARGE_NOMEM;

        ret = mem_cgroup_reclaim(mem_over_limit, gfp_mask, flags);
        if (mem_cgroup_margin(mem_over_limit) >= nr_pages)
                return CHARGE_RETRY;
        /*
         * Even though the limit is exceeded at this point, reclaim
         * may have been able to free some pages.  Retry the charge
         * before killing the task.
         *
         * Only for regular pages, though: huge pages are rather
         * unlikely to succeed so close to the limit, and we fall back
         * to regular pages anyway in case of failure.
         */
        if (nr_pages <= (1 << PAGE_ALLOC_COSTLY_ORDER) && ret)
                return CHARGE_RETRY;

        /*
         * At task move, charge accounts can be doubly counted. So, it's
         * better to wait until the end of task_move if something is going on.
         */
        if (mem_cgroup_wait_acct_move(mem_over_limit))
                return CHARGE_RETRY;

        /* If we don't need to call oom-killer at el, return immediately */
        if (!oom_check)
                return CHARGE_NOMEM;
        /* check OOM */
        if (!mem_cgroup_handle_oom(mem_over_limit, gfp_mask, get_order(csize)))
                return CHARGE_OOM_DIE;

        return CHARGE_RETRY;
}

/*
 * __mem_cgroup_try_charge() does
 * 1. detect memcg to be charged against from passed *mm and *ptr,
 * 2. update res_counter
 * 3. call memory reclaim if necessary.
 *
 * In some special case, if the task is fatal, fatal_signal_pending() or
 * has TIF_MEMDIE, this function returns -EINTR while writing root_mem_cgroup
 * to *ptr. There are two reasons for this. 1: fatal threads should quit as soon
 * as possible without any hazards. 2: all pages should have a valid
 * pc->mem_cgroup. If mm is NULL and the caller doesn't pass a valid memcg
 * pointer, that is treated as a charge to root_mem_cgroup.
 *
 * So __mem_cgroup_try_charge() will return
 *  0       ...  on success, filling *ptr with a valid memcg pointer.
 *  -ENOMEM ...  charge failure because of resource limits.
 *  -EINTR  ...  if thread is fatal. *ptr is filled with root_mem_cgroup.
 *
 * Unlike the exported interface, an "oom" parameter is added. if oom==true,
 * the oom-killer can be invoked.
 */
static int __mem_cgroup_try_charge(struct mm_struct *mm,
                                   gfp_t gfp_mask,
                                   unsigned int nr_pages,
                                   struct mem_cgroup **ptr,
                                   bool oom)
{
        unsigned int batch = max(CHARGE_BATCH, nr_pages);
        int nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES;
        struct mem_cgroup *memcg = NULL;
        int ret;

        /*
         * Unlike gloval-vm's OOM-kill, we're not in memory shortage
         * in system level. So, allow to go ahead dying process in addition to
         * MEMDIE process.
         */
        if (unlikely(test_thread_flag(TIF_MEMDIE)
                     || fatal_signal_pending(current)))
                goto bypass;

        /*
         * We always charge the cgroup the mm_struct belongs to.
         * The mm_struct's mem_cgroup changes on task migration if the
         * thread group leader migrates. It's possible that mm is not
         * set, if so charge the root memcg (happens for pagecache usage).
         */
        if (!*ptr && !mm)
                *ptr = root_mem_cgroup;
again:
        if (*ptr) { /* css should be a valid one */
                memcg = *ptr;
                if (mem_cgroup_is_root(memcg))
                        goto done;
                if (consume_stock(memcg, nr_pages))
                        goto done;
                css_get(&memcg->css);
        } else {
                struct task_struct *p;

                rcu_read_lock();
                p = rcu_dereference(mm->owner);
                /*
                 * Because we don't have task_lock(), "p" can exit.
                 * In that case, "memcg" can point to root or p can be NULL with
                 * race with swapoff. Then, we have small risk of mis-accouning.
                 * But such kind of mis-account by race always happens because
                 * we don't have cgroup_mutex(). It's overkill and we allo that
                 * small race, here.
                 * (*) swapoff at el will charge against mm-struct not against
                 * task-struct. So, mm->owner can be NULL.
                 */
                memcg = mem_cgroup_from_task(p);
                if (!memcg)
                        memcg = root_mem_cgroup;
                if (mem_cgroup_is_root(memcg)) {
                        rcu_read_unlock();
                        goto done;
                }
                if (consume_stock(memcg, nr_pages)) {
                        /*
                         * It seems dagerous to access memcg without css_get().
                         * But considering how consume_stok works, it's not
                         * necessary. If consume_stock success, some charges
                         * from this memcg are cached on this cpu. So, we
                         * don't need to call css_get()/css_tryget() before
                         * calling consume_stock().
                         */
                        rcu_read_unlock();
                        goto done;
                }
                /* after here, we may be blocked. we need to get refcnt */
                if (!css_tryget(&memcg->css)) {
                        rcu_read_unlock();
                        goto again;
                }
                rcu_read_unlock();
        }

        do {
                bool oom_check;

                /* If killed, bypass charge */
                if (fatal_signal_pending(current)) {
                        css_put(&memcg->css);
                        goto bypass;
                }

                oom_check = false;
                if (oom && !nr_oom_retries) {
                        oom_check = true;
                        nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES;
                }

                ret = mem_cgroup_do_charge(memcg, gfp_mask, batch, nr_pages,
                    oom_check);
                switch (ret) {
                case CHARGE_OK:
                        break;
                case CHARGE_RETRY: /* not in OOM situation but retry */
                        batch = nr_pages;
                        css_put(&memcg->css);
                        memcg = NULL;
                        goto again;
                case CHARGE_WOULDBLOCK: /* !__GFP_WAIT */
                        css_put(&memcg->css);
                        goto nomem;
                case CHARGE_NOMEM: /* OOM routine works */
                        if (!oom) {
                                css_put(&memcg->css);
                                goto nomem;
                        }
                        /* If oom, we never return -ENOMEM */
                        nr_oom_retries--;
                        break;
                case CHARGE_OOM_DIE: /* Killed by OOM Killer */
                        css_put(&memcg->css);
                        goto bypass;
                }
        } while (ret != CHARGE_OK);

        if (batch > nr_pages)
                refill_stock(memcg, batch - nr_pages);
        css_put(&memcg->css);
done:
        *ptr = memcg;
        return 0;
nomem:
        *ptr = NULL;
        return -ENOMEM;
bypass:
        *ptr = root_mem_cgroup;
        return -EINTR;
}

/*
 * Somemtimes we have to undo a charge we got by try_charge().
 * This function is for that and do uncharge, put css's refcnt.
 * gotten by try_charge().
 */
static void __mem_cgroup_cancel_charge(struct mem_cgroup *memcg,
                                       unsigned int nr_pages)
{
        if (!mem_cgroup_is_root(memcg)) {
                unsigned long bytes = nr_pages * PAGE_SIZE;

                res_counter_uncharge(&memcg->res, bytes);
                if (do_swap_account)
                        res_counter_uncharge(&memcg->memsw, bytes);
        }
}

/*
 * Cancel chrages in this cgroup....doesn't propagate to parent cgroup.
 * This is useful when moving usage to parent cgroup.
 */
static void __mem_cgroup_cancel_local_charge(struct mem_cgroup *memcg,
                                        unsigned int nr_pages)
{
        unsigned long bytes = nr_pages * PAGE_SIZE;

        if (mem_cgroup_is_root(memcg))
                return;

        res_counter_uncharge_until(&memcg->res, memcg->res.parent, bytes);
        if (do_swap_account)
                res_counter_uncharge_until(&memcg->memsw,
                                                memcg->memsw.parent, bytes);
}

/*
 * A helper function to get mem_cgroup from ID. must be called under
 * rcu_read_lock().  The caller is responsible for calling css_tryget if
 * the mem_cgroup is used for charging. (dropping refcnt from swap can be
 * called against removed memcg.)
 */
static struct mem_cgroup *mem_cgroup_lookup(unsigned short id)
{
        struct cgroup_subsys_state *css;

        /* ID 0 is unused ID */
        if (!id)
                return NULL;
        css = css_lookup(&mem_cgroup_subsys, id);
        if (!css)
                return NULL;
        return mem_cgroup_from_css(css);
}

struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
{
        struct mem_cgroup *memcg = NULL;
        struct page_cgroup *pc;
        unsigned short id;
        swp_entry_t ent;

        VM_BUG_ON(!PageLocked(page));

        pc = lookup_page_cgroup(page);
        lock_page_cgroup(pc);
        if (PageCgroupUsed(pc)) {
                memcg = pc->mem_cgroup;
                if (memcg && !css_tryget(&memcg->css))
                        memcg = NULL;
        } else if (PageSwapCache(page)) {
                ent.val = page_private(page);
                id = lookup_swap_cgroup_id(ent);
                rcu_read_lock();
                memcg = mem_cgroup_lookup(id);
                if (memcg && !css_tryget(&memcg->css))
                        memcg = NULL;
                rcu_read_unlock();
        }
        unlock_page_cgroup(pc);
        return memcg;
}

static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg,
                                       struct page *page,
                                       unsigned int nr_pages,
                                       enum charge_type ctype,
                                       bool lrucare)
{
        struct page_cgroup *pc = lookup_page_cgroup(page);
        struct zone *uninitialized_var(zone);
        struct lruvec *lruvec;
        bool was_on_lru = false;
        bool anon;

        lock_page_cgroup(pc);
        VM_BUG_ON(PageCgroupUsed(pc));
        /*
         * we don't need page_cgroup_lock about tail pages, becase they are not
         * accessed by any other context at this point.
         */

        /*
         * In some cases, SwapCache and FUSE(splice_buf->radixtree), the page
         * may already be on some other mem_cgroup's LRU.  Take care of it.
         */
        if (lrucare) {
                zone = page_zone(page);
                spin_lock_irq(&zone->lru_lock);
                if (PageLRU(page)) {
                        lruvec = mem_cgroup_zone_lruvec(zone, pc->mem_cgroup);
                        ClearPageLRU(page);
                        del_page_from_lru_list(page, lruvec, page_lru(page));
                        was_on_lru = true;
                }
        }

        pc->mem_cgroup = memcg;
        /*
         * We access a page_cgroup asynchronously without lock_page_cgroup().
         * Especially when a page_cgroup is taken from a page, pc->mem_cgroup
         * is accessed after testing USED bit. To make pc->mem_cgroup visible
         * before USED bit, we need memory barrier here.
         * See mem_cgroup_add_lru_list(), etc.
         */
        smp_wmb();
        SetPageCgroupUsed(pc);

        if (lrucare) {
                if (was_on_lru) {
                        lruvec = mem_cgroup_zone_lruvec(zone, pc->mem_cgroup);
                        VM_BUG_ON(PageLRU(page));
                        SetPageLRU(page);
                        add_page_to_lru_list(page, lruvec, page_lru(page));
                }
                spin_unlock_irq(&zone->lru_lock);
        }

        if (ctype == MEM_CGROUP_CHARGE_TYPE_ANON)
                anon = true;
        else
                anon = false;

        mem_cgroup_charge_statistics(memcg, page, anon, nr_pages);
        unlock_page_cgroup(pc);

        /*
         * "charge_statistics" updated event counter.
         */
        memcg_check_events(memcg, page);
}

static DEFINE_MUTEX(set_limit_mutex);

#ifdef CONFIG_MEMCG_KMEM
static inline bool memcg_can_account_kmem(struct mem_cgroup *memcg)
{
        return !mem_cgroup_disabled() && !mem_cgroup_is_root(memcg) &&
                (memcg->kmem_account_flags & KMEM_ACCOUNTED_MASK);
}

/*
 * This is a bit cumbersome, but it is rarely used and avoids a backpointer
 * in the memcg_cache_params struct.
 */
static struct kmem_cache *memcg_params_to_cache(struct memcg_cache_params *p)
{
        struct kmem_cache *cachep;

        VM_BUG_ON(p->is_root_cache);
        cachep = p->root_cache;
        return cachep->memcg_params->memcg_caches[memcg_cache_id(p->memcg)];
}

#ifdef CONFIG_SLABINFO
static int mem_cgroup_slabinfo_read(struct cgroup_subsys_state *css,
                                    struct cftype *cft, struct seq_file *m)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
        struct memcg_cache_params *params;

        if (!memcg_can_account_kmem(memcg))
                return -EIO;

        print_slabinfo_header(m);

        mutex_lock(&memcg->slab_caches_mutex);
        list_for_each_entry(params, &memcg->memcg_slab_caches, list)
                cache_show(memcg_params_to_cache(params), m);
        mutex_unlock(&memcg->slab_caches_mutex);

        return 0;
}
#endif

static int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp, u64 size)
{
        struct res_counter *fail_res;
        struct mem_cgroup *_memcg;
        int ret = 0;
        bool may_oom;

        ret = res_counter_charge(&memcg->kmem, size, &fail_res);
        if (ret)
                return ret;

        /*
         * Conditions under which we can wait for the oom_killer. Those are
         * the same conditions tested by the core page allocator
         */
        may_oom = (gfp & __GFP_FS) && !(gfp & __GFP_NORETRY);

        _memcg = memcg;
        ret = __mem_cgroup_try_charge(NULL, gfp, size >> PAGE_SHIFT,
                                      &_memcg, may_oom);

        if (ret == -EINTR)  {
                /*
                 * __mem_cgroup_try_charge() chosed to bypass to root due to
                 * OOM kill or fatal signal.  Since our only options are to
                 * either fail the allocation or charge it to this cgroup, do
                 * it as a temporary condition. But we can't fail. From a
                 * kmem/slab perspective, the cache has already been selected,
                 * by mem_cgroup_kmem_get_cache(), so it is too late to change
                 * our minds.
                 *
                 * This condition will only trigger if the task entered
                 * memcg_charge_kmem in a sane state, but was OOM-killed during
                 * __mem_cgroup_try_charge() above. Tasks that were already
                 * dying when the allocation triggers should have been already
                 * directed to the root cgroup in memcontrol.h
                 */
                res_counter_charge_nofail(&memcg->res, size, &fail_res);
                if (do_swap_account)
                        res_counter_charge_nofail(&memcg->memsw, size,
                                                  &fail_res);
                ret = 0;
        } else if (ret)
                res_counter_uncharge(&memcg->kmem, size);

        return ret;
}

static void memcg_uncharge_kmem(struct mem_cgroup *memcg, u64 size)
{
        res_counter_uncharge(&memcg->res, size);
        if (do_swap_account)
                res_counter_uncharge(&memcg->memsw, size);

        /* Not down to 0 */
        if (res_counter_uncharge(&memcg->kmem, size))
                return;

        /*
         * Releases a reference taken in kmem_cgroup_css_offline in case
         * this last uncharge is racing with the offlining code or it is
         * outliving the memcg existence.
         *
         * The memory barrier imposed by test&clear is paired with the
         * explicit one in memcg_kmem_mark_dead().
         */
        if (memcg_kmem_test_and_clear_dead(memcg))
                css_put(&memcg->css);
}

void memcg_cache_list_add(struct mem_cgroup *memcg, struct kmem_cache *cachep)
{
        if (!memcg)
                return;

        mutex_lock(&memcg->slab_caches_mutex);
        list_add(&cachep->memcg_params->list, &memcg->memcg_slab_caches);
        mutex_unlock(&memcg->slab_caches_mutex);
}

/*
 * helper for acessing a memcg's index. It will be used as an index in the
 * child cache array in kmem_cache, and also to derive its name. This function
 * will return -1 when this is not a kmem-limited memcg.
 */
int memcg_cache_id(struct mem_cgroup *memcg)
{
        return memcg ? memcg->kmemcg_id : -1;
}

/*
 * This ends up being protected by the set_limit mutex, during normal
 * operation, because that is its main call site.
 *
 * But when we create a new cache, we can call this as well if its parent
 * is kmem-limited. That will have to hold set_limit_mutex as well.
 */
int memcg_update_cache_sizes(struct mem_cgroup *memcg)
{
        int num, ret;

        num = ida_simple_get(&kmem_limited_groups,
                                0, MEMCG_CACHES_MAX_SIZE, GFP_KERNEL);
        if (num < 0)
                return num;
        /*
         * After this point, kmem_accounted (that we test atomically in
         * the beginning of this conditional), is no longer 0. This
         * guarantees only one process will set the following boolean
         * to true. We don't need test_and_set because we're protected
         * by the set_limit_mutex anyway.
         */
        memcg_kmem_set_activated(memcg);

        ret = memcg_update_all_caches(num+1);
        if (ret) {
                ida_simple_remove(&kmem_limited_groups, num);
                memcg_kmem_clear_activated(memcg);
                return ret;
        }

        memcg->kmemcg_id = num;
        INIT_LIST_HEAD(&memcg->memcg_slab_caches);
        mutex_init(&memcg->slab_caches_mutex);
        return 0;
}

static size_t memcg_caches_array_size(int num_groups)
{
        ssize_t size;
        if (num_groups <= 0)
                return 0;

        size = 2 * num_groups;
        if (size < MEMCG_CACHES_MIN_SIZE)
                size = MEMCG_CACHES_MIN_SIZE;
        else if (size > MEMCG_CACHES_MAX_SIZE)
                size = MEMCG_CACHES_MAX_SIZE;

        return size;
}

/*
 * We should update the current array size iff all caches updates succeed. This
 * can only be done from the slab side. The slab mutex needs to be held when
 * calling this.
 */
void memcg_update_array_size(int num)
{
        if (num > memcg_limited_groups_array_size)
                memcg_limited_groups_array_size = memcg_caches_array_size(num);
}

static void kmem_cache_destroy_work_func(struct work_struct *w);

int memcg_update_cache_size(struct kmem_cache *s, int num_groups)
{
        struct memcg_cache_params *cur_params = s->memcg_params;

        VM_BUG_ON(s->memcg_params && !s->memcg_params->is_root_cache);

        if (num_groups > memcg_limited_groups_array_size) {
                int i;
                ssize_t size = memcg_caches_array_size(num_groups);

                size *= sizeof(void *);
                size += offsetof(struct memcg_cache_params, memcg_caches);

                s->memcg_params = kzalloc(size, GFP_KERNEL);
                if (!s->memcg_params) {
                        s->memcg_params = cur_params;
                        return -ENOMEM;
                }

                s->memcg_params->is_root_cache = true;

                /*
                 * There is the chance it will be bigger than
                 * memcg_limited_groups_array_size, if we failed an allocation
                 * in a cache, in which case all caches updated before it, will
                 * have a bigger array.
                 *
                 * But if that is the case, the data after
                 * memcg_limited_groups_array_size is certainly unused
                 */
                for (i = 0; i < memcg_limited_groups_array_size; i++) {
                        if (!cur_params->memcg_caches[i])
                                continue;
                        s->memcg_params->memcg_caches[i] =
                                                cur_params->memcg_caches[i];
                }

                /*
                 * Ideally, we would wait until all caches succeed, and only
                 * then free the old one. But this is not worth the extra
                 * pointer per-cache we'd have to have for this.
                 *
                 * It is not a big deal if some caches are left with a size
                 * bigger than the others. And all updates will reset this
                 * anyway.
                 */
                kfree(cur_params);
        }
        return 0;
}

int memcg_register_cache(struct mem_cgroup *memcg, struct kmem_cache *s,
                         struct kmem_cache *root_cache)
{
        size_t size;

        if (!memcg_kmem_enabled())
                return 0;

        if (!memcg) {
                size = offsetof(struct memcg_cache_params, memcg_caches);
                size += memcg_limited_groups_array_size * sizeof(void *);
        } else
                size = sizeof(struct memcg_cache_params);

        s->memcg_params = kzalloc(size, GFP_KERNEL);
        if (!s->memcg_params)
                return -ENOMEM;

        if (memcg) {
                s->memcg_params->memcg = memcg;
                s->memcg_params->root_cache = root_cache;
                INIT_WORK(&s->memcg_params->destroy,
                                kmem_cache_destroy_work_func);
        } else
                s->memcg_params->is_root_cache = true;

        return 0;
}

void memcg_release_cache(struct kmem_cache *s)
{
        struct kmem_cache *root;
        struct mem_cgroup *memcg;
        int id;

        /*
         * This happens, for instance, when a root cache goes away before we
         * add any memcg.
         */
        if (!s->memcg_params)
                return;

        if (s->memcg_params->is_root_cache)
                goto out;

        memcg = s->memcg_params->memcg;
        id  = memcg_cache_id(memcg);

        root = s->memcg_params->root_cache;
        root->memcg_params->memcg_caches[id] = NULL;

        mutex_lock(&memcg->slab_caches_mutex);
        list_del(&s->memcg_params->list);
        mutex_unlock(&memcg->slab_caches_mutex);

        css_put(&memcg->css);
out:
        kfree(s->memcg_params);
}

/*
 * During the creation a new cache, we need to disable our accounting mechanism
 * altogether. This is true even if we are not creating, but rather just
 * enqueing new caches to be created.
 *
 * This is because that process will trigger allocations; some visible, like
 * explicit kmallocs to auxiliary data structures, name strings and internal
 * cache structures; some well concealed, like INIT_WORK() that can allocate
 * objects during debug.
 *
 * If any allocation happens during memcg_kmem_get_cache, we will recurse back
 * to it. This may not be a bounded recursion: since the first cache creation
 * failed to complete (waiting on the allocation), we'll just try to create the
 * cache again, failing at the same point.
 *
 * memcg_kmem_get_cache is prepared to abort after seeing a positive count of
 * memcg_kmem_skip_account. So we enclose anything that might allocate memory
 * inside the following two functions.
 */
static inline void memcg_stop_kmem_account(void)
{
        VM_BUG_ON(!current->mm);
        current->memcg_kmem_skip_account++;
}

static inline void memcg_resume_kmem_account(void)
{
        VM_BUG_ON(!current->mm);
        current->memcg_kmem_skip_account--;
}

static void kmem_cache_destroy_work_func(struct work_struct *w)
{
        struct kmem_cache *cachep;
        struct memcg_cache_params *p;

        p = container_of(w, struct memcg_cache_params, destroy);

        cachep = memcg_params_to_cache(p);

        /*
         * If we get down to 0 after shrink, we could delete right away.
         * However, memcg_release_pages() already puts us back in the workqueue
         * in that case. If we proceed deleting, we'll get a dangling
         * reference, and removing the object from the workqueue in that case
         * is unnecessary complication. We are not a fast path.
         *
         * Note that this case is fundamentally different from racing with
         * shrink_slab(): if memcg_cgroup_destroy_cache() is called in
         * kmem_cache_shrink, not only we would be reinserting a dead cache
         * into the queue, but doing so from inside the worker racing to
         * destroy it.
         *
         * So if we aren't down to zero, we'll just schedule a worker and try
         * again
         */
        if (atomic_read(&cachep->memcg_params->nr_pages) != 0) {
                kmem_cache_shrink(cachep);
                if (atomic_read(&cachep->memcg_params->nr_pages) == 0)
                        return;
        } else
                kmem_cache_destroy(cachep);
}

void mem_cgroup_destroy_cache(struct kmem_cache *cachep)
{
        if (!cachep->memcg_params->dead)
                return;

        /*
         * There are many ways in which we can get here.
         *
         * We can get to a memory-pressure situation while the delayed work is
         * still pending to run. The vmscan shrinkers can then release all
         * cache memory and get us to destruction. If this is the case, we'll
         * be executed twice, which is a bug (the second time will execute over
         * bogus data). In this case, cancelling the work should be fine.
         *
         * But we can also get here from the worker itself, if
         * kmem_cache_shrink is enough to shake all the remaining objects and
         * get the page count to 0. In this case, we'll deadlock if we try to
         * cancel the work (the worker runs with an internal lock held, which
         * is the same lock we would hold for cancel_work_sync().)
         *
         * Since we can't possibly know who got us here, just refrain from
         * running if there is already work pending
         */
        if (work_pending(&cachep->memcg_params->destroy))
                return;
        /*
         * We have to defer the actual destroying to a workqueue, because
         * we might currently be in a context that cannot sleep.
         */
        schedule_work(&cachep->memcg_params->destroy);
}

/*
 * This lock protects updaters, not readers. We want readers to be as fast as
 * they can, and they will either see NULL or a valid cache value. Our model
 * allow them to see NULL, in which case the root memcg will be selected.
 *
 * We need this lock because multiple allocations to the same cache from a non
 * will span more than one worker. Only one of them can create the cache.
 */
static DEFINE_MUTEX(memcg_cache_mutex);

/*
 * Called with memcg_cache_mutex held
 */
static struct kmem_cache *kmem_cache_dup(struct mem_cgroup *memcg,
                                         struct kmem_cache *s)
{
        struct kmem_cache *new;
        static char *tmp_name = NULL;

        lockdep_assert_held(&memcg_cache_mutex);

        /*
         * kmem_cache_create_memcg duplicates the given name and
         * cgroup_name for this name requires RCU context.
         * This static temporary buffer is used to prevent from
         * pointless shortliving allocation.
         */
        if (!tmp_name) {
                tmp_name = kmalloc(PATH_MAX, GFP_KERNEL);
                if (!tmp_name)
                        return NULL;
        }

        rcu_read_lock();
        snprintf(tmp_name, PATH_MAX, "%s(%d:%s)", s->name,
                         memcg_cache_id(memcg), cgroup_name(memcg->css.cgroup));
        rcu_read_unlock();

        new = kmem_cache_create_memcg(memcg, tmp_name, s->object_size, s->align,
                                      (s->flags & ~SLAB_PANIC), s->ctor, s);

        if (new)
                new->allocflags |= __GFP_KMEMCG;

        return new;
}

static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
                                                  struct kmem_cache *cachep)
{
        struct kmem_cache *new_cachep;
        int idx;

        BUG_ON(!memcg_can_account_kmem(memcg));

        idx = memcg_cache_id(memcg);

        mutex_lock(&memcg_cache_mutex);
        new_cachep = cachep->memcg_params->memcg_caches[idx];
        if (new_cachep) {
                css_put(&memcg->css);
                goto out;
        }

        new_cachep = kmem_cache_dup(memcg, cachep);
        if (new_cachep == NULL) {
                new_cachep = cachep;
                css_put(&memcg->css);
                goto out;
        }

        atomic_set(&new_cachep->memcg_params->nr_pages , 0);

        cachep->memcg_params->memcg_caches[idx] = new_cachep;
        /*
         * the readers won't lock, make sure everybody sees the updated value,
         * so they won't put stuff in the queue again for no reason
         */
        wmb();
out:
        mutex_unlock(&memcg_cache_mutex);
        return new_cachep;
}

void kmem_cache_destroy_memcg_children(struct kmem_cache *s)
{
        struct kmem_cache *c;
        int i;

        if (!s->memcg_params)
                return;
        if (!s->memcg_params->is_root_cache)
                return;

        /*
         * If the cache is being destroyed, we trust that there is no one else
         * requesting objects from it. Even if there are, the sanity checks in
         * kmem_cache_destroy should caught this ill-case.
         *
         * Still, we don't want anyone else freeing memcg_caches under our
         * noses, which can happen if a new memcg comes to life. As usual,
         * we'll take the set_limit_mutex to protect ourselves against this.
         */
        mutex_lock(&set_limit_mutex);
        for (i = 0; i < memcg_limited_groups_array_size; i++) {
                c = s->memcg_params->memcg_caches[i];
                if (!c)
                        continue;

                /*
                 * We will now manually delete the caches, so to avoid races
                 * we need to cancel all pending destruction workers and
                 * proceed with destruction ourselves.
                 *
                 * kmem_cache_destroy() will call kmem_cache_shrink internally,
                 * and that could spawn the workers again: it is likely that
                 * the cache still have active pages until this very moment.
                 * This would lead us back to mem_cgroup_destroy_cache.
                 *
                 * But that will not execute at all if the "dead" flag is not
                 * set, so flip it down to guarantee we are in control.
                 */
                c->memcg_params->dead = false;
                cancel_work_sync(&c->memcg_params->destroy);
                kmem_cache_destroy(c);
        }
        mutex_unlock(&set_limit_mutex);
}

struct create_work {
        struct mem_cgroup *memcg;
        struct kmem_cache *cachep;
        struct work_struct work;
};

static void mem_cgroup_destroy_all_caches(struct mem_cgroup *memcg)
{
        struct kmem_cache *cachep;
        struct memcg_cache_params *params;

        if (!memcg_kmem_is_active(memcg))
                return;

        mutex_lock(&memcg->slab_caches_mutex);
        list_for_each_entry(params, &memcg->memcg_slab_caches, list) {
                cachep = memcg_params_to_cache(params);
                cachep->memcg_params->dead = true;
                schedule_work(&cachep->memcg_params->destroy);
        }
        mutex_unlock(&memcg->slab_caches_mutex);
}

static void memcg_create_cache_work_func(struct work_struct *w)
{
        struct create_work *cw;

        cw = container_of(w, struct create_work, work);
        memcg_create_kmem_cache(cw->memcg, cw->cachep);
        kfree(cw);
}

/*
 * Enqueue the creation of a per-memcg kmem_cache.
 */
static void __memcg_create_cache_enqueue(struct mem_cgroup *memcg,
                                         struct kmem_cache *cachep)
{
        struct create_work *cw;

        cw = kmalloc(sizeof(struct create_work), GFP_NOWAIT);
        if (cw == NULL) {
                css_put(&memcg->css);
                return;
        }

        cw->memcg = memcg;
        cw->cachep = cachep;

        INIT_WORK(&cw->work, memcg_create_cache_work_func);
        schedule_work(&cw->work);
}

static void memcg_create_cache_enqueue(struct mem_cgroup *memcg,
                                       struct kmem_cache *cachep)
{
        /*
         * We need to stop accounting when we kmalloc, because if the
         * corresponding kmalloc cache is not yet created, the first allocation
         * in __memcg_create_cache_enqueue will recurse.
         *
         * However, it is better to enclose the whole function. Depending on
         * the debugging options enabled, INIT_WORK(), for instance, can
         * trigger an allocation. This too, will make us recurse. Because at
         * this point we can't allow ourselves back into memcg_kmem_get_cache,
         * the safest choice is to do it like this, wrapping the whole function.
         */
        memcg_stop_kmem_account();
        __memcg_create_cache_enqueue(memcg, cachep);
        memcg_resume_kmem_account();
}
/*
 * Return the kmem_cache we're supposed to use for a slab allocation.
 * We try to use the current memcg's version of the cache.
 *
 * If the cache does not exist yet, if we are the first user of it,
 * we either create it immediately, if possible, or create it asynchronously
 * in a workqueue.
 * In the latter case, we will let the current allocation go through with
 * the original cache.
 *
 * Can't be called in interrupt context or from kernel threads.
 * This function needs to be called with rcu_read_lock() held.
 */
struct kmem_cache *__memcg_kmem_get_cache(struct kmem_cache *cachep,
                                          gfp_t gfp)
{
        struct mem_cgroup *memcg;
        int idx;

        VM_BUG_ON(!cachep->memcg_params);
        VM_BUG_ON(!cachep->memcg_params->is_root_cache);

        if (!current->mm || current->memcg_kmem_skip_account)
                return cachep;

        rcu_read_lock();
        memcg = mem_cgroup_from_task(rcu_dereference(current->mm->owner));

        if (!memcg_can_account_kmem(memcg))
                goto out;

        idx = memcg_cache_id(memcg);

        /*
         * barrier to mare sure we're always seeing the up to date value.  The
         * code updating memcg_caches will issue a write barrier to match this.
         */
        read_barrier_depends();
        if (likely(cachep->memcg_params->memcg_caches[idx])) {
                cachep = cachep->memcg_params->memcg_caches[idx];
                goto out;
        }

        /* The corresponding put will be done in the workqueue. */
        if (!css_tryget(&memcg->css))
                goto out;
        rcu_read_unlock();

        /*
         * If we are in a safe context (can wait, and not in interrupt
         * context), we could be be predictable and return right away.
         * This would guarantee that the allocation being performed
         * already belongs in the new cache.
         *
         * However, there are some clashes that can arrive from locking.
         * For instance, because we acquire the slab_mutex while doing
         * kmem_cache_dup, this means no further allocation could happen
         * with the slab_mutex held.
         *
         * Also, because cache creation issue get_online_cpus(), this
         * creates a lock chain: memcg_slab_mutex -> cpu_hotplug_mutex,
         * that ends up reversed during cpu hotplug. (cpuset allocates
         * a bunch of GFP_KERNEL memory during cpuup). Due to all that,
         * better to defer everything.
         */
        memcg_create_cache_enqueue(memcg, cachep);
        return cachep;
out:
        rcu_read_unlock();
        return cachep;
}
EXPORT_SYMBOL(__memcg_kmem_get_cache);

/*
 * We need to verify if the allocation against current->mm->owner's memcg is
 * possible for the given order. But the page is not allocated yet, so we'll
 * need a further commit step to do the final arrangements.
 *
 * It is possible for the task to switch cgroups in this mean time, so at
 * commit time, we can't rely on task conversion any longer.  We'll then use
 * the handle argument to return to the caller which cgroup we should commit
 * against. We could also return the memcg directly and avoid the pointer
 * passing, but a boolean return value gives better semantics considering
 * the compiled-out case as well.
 *
 * Returning true means the allocation is possible.
 */
bool
__memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **_memcg, int order)
{
        struct mem_cgroup *memcg;
        int ret;

        *_memcg = NULL;

        /*
         * Disabling accounting is only relevant for some specific memcg
         * internal allocations. Therefore we would initially not have such
         * check here, since direct calls to the page allocator that are marked
         * with GFP_KMEMCG only happen outside memcg core. We are mostly
         * concerned with cache allocations, and by having this test at
         * memcg_kmem_get_cache, we are already able to relay the allocation to
         * the root cache and bypass the memcg cache altogether.
         *
         * There is one exception, though: the SLUB allocator does not create
         * large order caches, but rather service large kmallocs directly from
         * the page allocator. Therefore, the following sequence when backed by
         * the SLUB allocator:
         *
         *      memcg_stop_kmem_account();
         *      kmalloc(<large_number>)
         *      memcg_resume_kmem_account();
         *
         * would effectively ignore the fact that we should skip accounting,
         * since it will drive us directly to this function without passing
         * through the cache selector memcg_kmem_get_cache. Such large
         * allocations are extremely rare but can happen, for instance, for the
         * cache arrays. We bring this test here.
         */
        if (!current->mm || current->memcg_kmem_skip_account)
                return true;

        memcg = try_get_mem_cgroup_from_mm(current->mm);

        /*
         * very rare case described in mem_cgroup_from_task. Unfortunately there
         * isn't much we can do without complicating this too much, and it would
         * be gfp-dependent anyway. Just let it go
         */
        if (unlikely(!memcg))
                return true;

        if (!memcg_can_account_kmem(memcg)) {
                css_put(&memcg->css);
                return true;
        }

        ret = memcg_charge_kmem(memcg, gfp, PAGE_SIZE << order);
        if (!ret)
                *_memcg = memcg;

        css_put(&memcg->css);
        return (ret == 0);
}

void __memcg_kmem_commit_charge(struct page *page, struct mem_cgroup *memcg,
                              int order)
{
        struct page_cgroup *pc;

        VM_BUG_ON(mem_cgroup_is_root(memcg));

        /* The page allocation failed. Revert */
        if (!page) {
                memcg_uncharge_kmem(memcg, PAGE_SIZE << order);
                return;
        }

        pc = lookup_page_cgroup(page);
        lock_page_cgroup(pc);
        pc->mem_cgroup = memcg;
        SetPageCgroupUsed(pc);
        unlock_page_cgroup(pc);
}

void __memcg_kmem_uncharge_pages(struct page *page, int order)
{
        struct mem_cgroup *memcg = NULL;
        struct page_cgroup *pc;


        pc = lookup_page_cgroup(page);
        /*
         * Fast unlocked return. Theoretically might have changed, have to
         * check again after locking.
         */
        if (!PageCgroupUsed(pc))
                return;

        lock_page_cgroup(pc);
        if (PageCgroupUsed(pc)) {
                memcg = pc->mem_cgroup;
                ClearPageCgroupUsed(pc);
        }
        unlock_page_cgroup(pc);

        /*
         * We trust that only if there is a memcg associated with the page, it
         * is a valid allocation
         */
        if (!memcg)
                return;

        VM_BUG_ON(mem_cgroup_is_root(memcg));
        memcg_uncharge_kmem(memcg, PAGE_SIZE << order);
}
#else
static inline void mem_cgroup_destroy_all_caches(struct mem_cgroup *memcg)
{
}
#endif /* CONFIG_MEMCG_KMEM */

#ifdef CONFIG_TRANSPARENT_HUGEPAGE

#define PCGF_NOCOPY_AT_SPLIT (1 << PCG_LOCK | 1 << PCG_MIGRATION)
/*
 * Because tail pages are not marked as "used", set it. We're under
 * zone->lru_lock, 'splitting on pmd' and compound_lock.
 * charge/uncharge will be never happen and move_account() is done under
 * compound_lock(), so we don't have to take care of races.
 */
void mem_cgroup_split_huge_fixup(struct page *head)
{
        struct page_cgroup *head_pc = lookup_page_cgroup(head);
        struct page_cgroup *pc;
        struct mem_cgroup *memcg;
        int i;

        if (mem_cgroup_disabled())
                return;

        memcg = head_pc->mem_cgroup;
        for (i = 1; i < HPAGE_PMD_NR; i++) {
                pc = head_pc + i;
                pc->mem_cgroup = memcg;
                smp_wmb();/* see __commit_charge() */
                pc->flags = head_pc->flags & ~PCGF_NOCOPY_AT_SPLIT;
        }
        __this_cpu_sub(memcg->stat->count[MEM_CGROUP_STAT_RSS_HUGE],
                       HPAGE_PMD_NR);
}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */

/**
 * mem_cgroup_move_account - move account of the page
 * @page: the page
 * @nr_pages: number of regular pages (>1 for huge pages)
 * @pc: page_cgroup of the page.
 * @from: mem_cgroup which the page is moved from.
 * @to: mem_cgroup which the page is moved to. @from != @to.
 *
 * The caller must confirm following.
 * - page is not on LRU (isolate_page() is useful.)
 * - compound_lock is held when nr_pages > 1
 *
 * This function doesn't do "charge" to new cgroup and doesn't do "uncharge"
 * from old cgroup.
 */
static int mem_cgroup_move_account(struct page *page,
                                   unsigned int nr_pages,
                                   struct page_cgroup *pc,
                                   struct mem_cgroup *from,
                                   struct mem_cgroup *to)
{
        unsigned long flags;
        int ret;
        bool anon = PageAnon(page);

        VM_BUG_ON(from == to);
        VM_BUG_ON(PageLRU(page));
        /*
         * The page is isolated from LRU. So, collapse function
         * will not handle this page. But page splitting can happen.
         * Do this check under compound_page_lock(). The caller should
         * hold it.
         */
        ret = -EBUSY;
        if (nr_pages > 1 && !PageTransHuge(page))
                goto out;

        lock_page_cgroup(pc);

        ret = -EINVAL;
        if (!PageCgroupUsed(pc) || pc->mem_cgroup != from)
                goto unlock;

        move_lock_mem_cgroup(from, &flags);

        if (!anon && page_mapped(page)) {
                /* Update mapped_file data for mem_cgroup */
                preempt_disable();
                __this_cpu_dec(from->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
                __this_cpu_inc(to->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
                preempt_enable();
        }
        mem_cgroup_charge_statistics(from, page, anon, -nr_pages);

        /* caller should have done css_get */
        pc->mem_cgroup = to;
        mem_cgroup_charge_statistics(to, page, anon, nr_pages);
        move_unlock_mem_cgroup(from, &flags);
        ret = 0;
unlock:
        unlock_page_cgroup(pc);
        /*
         * check events
         */
        memcg_check_events(to, page);
        memcg_check_events(from, page);
out:
        return ret;
}

/**
 * mem_cgroup_move_parent - moves page to the parent group
 * @page: the page to move
 * @pc: page_cgroup of the page
 * @child: page's cgroup
 *
 * move charges to its parent or the root cgroup if the group has no
 * parent (aka use_hierarchy==0).
 * Although this might fail (get_page_unless_zero, isolate_lru_page or
 * mem_cgroup_move_account fails) the failure is always temporary and
 * it signals a race with a page removal/uncharge or migration. In the
 * first case the page is on the way out and it will vanish from the LRU
 * on the next attempt and the call should be retried later.
 * Isolation from the LRU fails only if page has been isolated from
 * the LRU since we looked at it and that usually means either global
 * reclaim or migration going on. The page will either get back to the
 * LRU or vanish.
 * Finaly mem_cgroup_move_account fails only if the page got uncharged
 * (!PageCgroupUsed) or moved to a different group. The page will
 * disappear in the next attempt.
 */
static int mem_cgroup_move_parent(struct page *page,
                                  struct page_cgroup *pc,
                                  struct mem_cgroup *child)
{
        struct mem_cgroup *parent;
        unsigned int nr_pages;
        unsigned long uninitialized_var(flags);
        int ret;

        VM_BUG_ON(mem_cgroup_is_root(child));

        ret = -EBUSY;
        if (!get_page_unless_zero(page))
                goto out;
        if (isolate_lru_page(page))
                goto put;

        nr_pages = hpage_nr_pages(page);

        parent = parent_mem_cgroup(child);
        /*
         * If no parent, move charges to root cgroup.
         */
        if (!parent)
                parent = root_mem_cgroup;

        if (nr_pages > 1) {
                VM_BUG_ON(!PageTransHuge(page));
                flags = compound_lock_irqsave(page);
        }

        ret = mem_cgroup_move_account(page, nr_pages,
                                pc, child, parent);
        if (!ret)
                __mem_cgroup_cancel_local_charge(child, nr_pages);

        if (nr_pages > 1)
                compound_unlock_irqrestore(page, flags);
        putback_lru_page(page);
put:
        put_page(page);
out:
        return ret;
}

/*
 * Charge the memory controller for page usage.
 * Return
 * 0 if the charge was successful
 * < 0 if the cgroup is over its limit
 */
static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
                                gfp_t gfp_mask, enum charge_type ctype)
{
        struct mem_cgroup *memcg = NULL;
        unsigned int nr_pages = 1;
        bool oom = true;
        int ret;

        if (PageTransHuge(page)) {
                nr_pages <<= compound_order(page);
                VM_BUG_ON(!PageTransHuge(page));
                /*
                 * Never OOM-kill a process for a huge page.  The
                 * fault handler will fall back to regular pages.
                 */
                oom = false;
        }

        ret = __mem_cgroup_try_charge(mm, gfp_mask, nr_pages, &memcg, oom);
        if (ret == -ENOMEM)
                return ret;
        __mem_cgroup_commit_charge(memcg, page, nr_pages, ctype, false);
        return 0;
}

int mem_cgroup_newpage_charge(struct page *page,
                              struct mm_struct *mm, gfp_t gfp_mask)
{
        if (mem_cgroup_disabled())
                return 0;
        VM_BUG_ON(page_mapped(page));
        VM_BUG_ON(page->mapping && !PageAnon(page));
        VM_BUG_ON(!mm);
        return mem_cgroup_charge_common(page, mm, gfp_mask,
                                        MEM_CGROUP_CHARGE_TYPE_ANON);
}

/*
 * While swap-in, try_charge -> commit or cancel, the page is locked.
 * And when try_charge() successfully returns, one refcnt to memcg without
 * struct page_cgroup is acquired. This refcnt will be consumed by
 * "commit()" or removed by "cancel()"
 */
static int __mem_cgroup_try_charge_swapin(struct mm_struct *mm,
                                          struct page *page,
                                          gfp_t mask,
                                          struct mem_cgroup **memcgp)
{
        struct mem_cgroup *memcg;
        struct page_cgroup *pc;
        int ret;

        pc = lookup_page_cgroup(page);
        /*
         * Every swap fault against a single page tries to charge the
         * page, bail as early as possible.  shmem_unuse() encounters
         * already charged pages, too.  The USED bit is protected by
         * the page lock, which serializes swap cache removal, which
         * in turn serializes uncharging.
         */
        if (PageCgroupUsed(pc))
                return 0;
        if (!do_swap_account)
                goto charge_cur_mm;
        memcg = try_get_mem_cgroup_from_page(page);
        if (!memcg)
                goto charge_cur_mm;
        *memcgp = memcg;
        ret = __mem_cgroup_try_charge(NULL, mask, 1, memcgp, true);
        css_put(&memcg->css);
        if (ret == -EINTR)
                ret = 0;
        return ret;
charge_cur_mm:
        ret = __mem_cgroup_try_charge(mm, mask, 1, memcgp, true);
        if (ret == -EINTR)
                ret = 0;
        return ret;
}

int mem_cgroup_try_charge_swapin(struct mm_struct *mm, struct page *page,
                                 gfp_t gfp_mask, struct mem_cgroup **memcgp)
{
        *memcgp = NULL;
        if (mem_cgroup_disabled())
                return 0;
        /*
         * A racing thread's fault, or swapoff, may have already
         * updated the pte, and even removed page from swap cache: in
         * those cases unuse_pte()'s pte_same() test will fail; but
         * there's also a KSM case which does need to charge the page.
         */
        if (!PageSwapCache(page)) {
                int ret;

                ret = __mem_cgroup_try_charge(mm, gfp_mask, 1, memcgp, true);
                if (ret == -EINTR)
                        ret = 0;
                return ret;
        }
        return __mem_cgroup_try_charge_swapin(mm, page, gfp_mask, memcgp);
}

void mem_cgroup_cancel_charge_swapin(struct mem_cgroup *memcg)
{
        if (mem_cgroup_disabled())
                return;
        if (!memcg)
                return;
        __mem_cgroup_cancel_charge(memcg, 1);
}

static void
__mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *memcg,
                                        enum charge_type ctype)
{
        if (mem_cgroup_disabled())
                return;
        if (!memcg)
                return;

        __mem_cgroup_commit_charge(memcg, page, 1, ctype, true);
        /*
         * Now swap is on-memory. This means this page may be
         * counted both as mem and swap....double count.
         * Fix it by uncharging from memsw. Basically, this SwapCache is stable
         * under lock_page(). But in do_swap_page()::memory.c, reuse_swap_page()
         * may call delete_from_swap_cache() before reach here.
         */
        if (do_swap_account && PageSwapCache(page)) {
                swp_entry_t ent = {.val = page_private(page)};
                mem_cgroup_uncharge_swap(ent);
        }
}

void mem_cgroup_commit_charge_swapin(struct page *page,
                                     struct mem_cgroup *memcg)
{
        __mem_cgroup_commit_charge_swapin(page, memcg,
                                          MEM_CGROUP_CHARGE_TYPE_ANON);
}

int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
                                gfp_t gfp_mask)
{
        struct mem_cgroup *memcg = NULL;
        enum charge_type type = MEM_CGROUP_CHARGE_TYPE_CACHE;
        int ret;

        if (mem_cgroup_disabled())
                return 0;
        if (PageCompound(page))
                return 0;

        if (!PageSwapCache(page))
                ret = mem_cgroup_charge_common(page, mm, gfp_mask, type);
        else { /* page is swapcache/shmem */
                ret = __mem_cgroup_try_charge_swapin(mm, page,
                                                     gfp_mask, &memcg);
                if (!ret)
                        __mem_cgroup_commit_charge_swapin(page, memcg, type);
        }
        return ret;
}

static void mem_cgroup_do_uncharge(struct mem_cgroup *memcg,
                                   unsigned int nr_pages,
                                   const enum charge_type ctype)
{
        struct memcg_batch_info *batch = NULL;
        bool uncharge_memsw = true;

        /* If swapout, usage of swap doesn't decrease */
        if (!do_swap_account || ctype == MEM_CGROUP_CHARGE_TYPE_SWAPOUT)
                uncharge_memsw = false;

        batch = &current->memcg_batch;
        /*
         * In usual, we do css_get() when we remember memcg pointer.
         * But in this case, we keep res->usage until end of a series of
         * uncharges. Then, it's ok to ignore memcg's refcnt.
         */
        if (!batch->memcg)
                batch->memcg = memcg;
        /*
         * do_batch > 0 when unmapping pages or inode invalidate/truncate.
         * In those cases, all pages freed continuously can be expected to be in
         * the same cgroup and we have chance to coalesce uncharges.
         * But we do uncharge one by one if this is killed by OOM(TIF_MEMDIE)
         * because we want to do uncharge as soon as possible.
         */

        if (!batch->do_batch || test_thread_flag(TIF_MEMDIE))
                goto direct_uncharge;

        if (nr_pages > 1)
                goto direct_uncharge;

        /*
         * In typical case, batch->memcg == mem. This means we can
         * merge a series of uncharges to an uncharge of res_counter.
         * If not, we uncharge res_counter ony by one.
         */
        if (batch->memcg != memcg)
                goto direct_uncharge;
        /* remember freed charge and uncharge it later */
        batch->nr_pages++;
        if (uncharge_memsw)
                batch->memsw_nr_pages++;
        return;
direct_uncharge:
        res_counter_uncharge(&memcg->res, nr_pages * PAGE_SIZE);
        if (uncharge_memsw)
                res_counter_uncharge(&memcg->memsw, nr_pages * PAGE_SIZE);
        if (unlikely(batch->memcg != memcg))
                memcg_oom_recover(memcg);
}

/*
 * uncharge if !page_mapped(page)
 */
static struct mem_cgroup *
__mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype,
                             bool end_migration)
{
        struct mem_cgroup *memcg = NULL;
        unsigned int nr_pages = 1;
        struct page_cgroup *pc;
        bool anon;

        if (mem_cgroup_disabled())
                return NULL;

        if (PageTransHuge(page)) {
                nr_pages <<= compound_order(page);
                VM_BUG_ON(!PageTransHuge(page));
        }
        /*
         * Check if our page_cgroup is valid
         */
        pc = lookup_page_cgroup(page);
        if (unlikely(!PageCgroupUsed(pc)))
                return NULL;

        lock_page_cgroup(pc);

        memcg = pc->mem_cgroup;

        if (!PageCgroupUsed(pc))
                goto unlock_out;

        anon = PageAnon(page);

        switch (ctype) {
        case MEM_CGROUP_CHARGE_TYPE_ANON:
                /*
                 * Generally PageAnon tells if it's the anon statistics to be
                 * updated; but sometimes e.g. mem_cgroup_uncharge_page() is
                 * used before page reached the stage of being marked PageAnon.
                 */
                anon = true;
                /* fallthrough */
        case MEM_CGROUP_CHARGE_TYPE_DROP:
                /* See mem_cgroup_prepare_migration() */
                if (page_mapped(page))
                        goto unlock_out;
                /*
                 * Pages under migration may not be uncharged.  But
                 * end_migration() /must/ be the one uncharging the
                 * unused post-migration page and so it has to call
                 * here with the migration bit still set.  See the
                 * res_counter handling below.
                 */
                if (!end_migration && PageCgroupMigration(pc))
                        goto unlock_out;
                break;
        case MEM_CGROUP_CHARGE_TYPE_SWAPOUT:
                if (!PageAnon(page)) {  /* Shared memory */
                        if (page->mapping && !page_is_file_cache(page))
                                goto unlock_out;
                } else if (page_mapped(page)) /* Anon */
                                goto unlock_out;
                break;
        default:
                break;
        }

        mem_cgroup_charge_statistics(memcg, page, anon, -nr_pages);

        ClearPageCgroupUsed(pc);
        /*
         * pc->mem_cgroup is not cleared here. It will be accessed when it's
         * freed from LRU. This is safe because uncharged page is expected not
         * to be reused (freed soon). Exception is SwapCache, it's handled by
         * special functions.
         */

        unlock_page_cgroup(pc);
        /*
         * even after unlock, we have memcg->res.usage here and this memcg
         * will never be freed, so it's safe to call css_get().
         */
        memcg_check_events(memcg, page);
        if (do_swap_account && ctype == MEM_CGROUP_CHARGE_TYPE_SWAPOUT) {
                mem_cgroup_swap_statistics(memcg, true);
                css_get(&memcg->css);
        }
        /*
         * Migration does not charge the res_counter for the
         * replacement page, so leave it alone when phasing out the
         * page that is unused after the migration.
         */
        if (!end_migration && !mem_cgroup_is_root(memcg))
                mem_cgroup_do_uncharge(memcg, nr_pages, ctype);

        return memcg;

unlock_out:
        unlock_page_cgroup(pc);
        return NULL;
}

void mem_cgroup_uncharge_page(struct page *page)
{
        /* early check. */
        if (page_mapped(page))
                return;
        VM_BUG_ON(page->mapping && !PageAnon(page));
        /*
         * If the page is in swap cache, uncharge should be deferred
         * to the swap path, which also properly accounts swap usage
         * and handles memcg lifetime.
         *
         * Note that this check is not stable and reclaim may add the
         * page to swap cache at any time after this.  However, if the
         * page is not in swap cache by the time page->mapcount hits
         * 0, there won't be any page table references to the swap
         * slot, and reclaim will free it and not actually write the
         * page to disk.
         */
        if (PageSwapCache(page))
                return;
        __mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_ANON, false);
}

void mem_cgroup_uncharge_cache_page(struct page *page)
{
        VM_BUG_ON(page_mapped(page));
        VM_BUG_ON(page->mapping);
        __mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_CACHE, false);
}

/*
 * Batch_start/batch_end is called in unmap_page_range/invlidate/trucate.
 * In that cases, pages are freed continuously and we can expect pages
 * are in the same memcg. All these calls itself limits the number of
 * pages freed at once, then uncharge_start/end() is called properly.
 * This may be called prural(2) times in a context,
 */

void mem_cgroup_uncharge_start(void)
{
        current->memcg_batch.do_batch++;
        /* We can do nest. */
        if (current->memcg_batch.do_batch == 1) {
                current->memcg_batch.memcg = NULL;
                current->memcg_batch.nr_pages = 0;
                current->memcg_batch.memsw_nr_pages = 0;
        }
}

void mem_cgroup_uncharge_end(void)
{
        struct memcg_batch_info *batch = &current->memcg_batch;

        if (!batch->do_batch)
                return;

        batch->do_batch--;
        if (batch->do_batch) /* If stacked, do nothing. */
                return;

        if (!batch->memcg)
                return;
        /*
         * This "batch->memcg" is valid without any css_get/put etc...
         * bacause we hide charges behind us.
         */
        if (batch->nr_pages)
                res_counter_uncharge(&batch->memcg->res,
                                     batch->nr_pages * PAGE_SIZE);
        if (batch->memsw_nr_pages)
                res_counter_uncharge(&batch->memcg->memsw,
                                     batch->memsw_nr_pages * PAGE_SIZE);
        memcg_oom_recover(batch->memcg);
        /* forget this pointer (for sanity check) */
        batch->memcg = NULL;
}

#ifdef CONFIG_SWAP
/*
 * called after __delete_from_swap_cache() and drop "page" account.
 * memcg information is recorded to swap_cgroup of "ent"
 */
void
mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout)
{
        struct mem_cgroup *memcg;
        int ctype = MEM_CGROUP_CHARGE_TYPE_SWAPOUT;

        if (!swapout) /* this was a swap cache but the swap is unused ! */
                ctype = MEM_CGROUP_CHARGE_TYPE_DROP;

        memcg = __mem_cgroup_uncharge_common(page, ctype, false);

        /*
         * record memcg information,  if swapout && memcg != NULL,
         * css_get() was called in uncharge().
         */
        if (do_swap_account && swapout && memcg)
                swap_cgroup_record(ent, css_id(&memcg->css));
}
#endif

#ifdef CONFIG_MEMCG_SWAP
/*
 * called from swap_entry_free(). remove record in swap_cgroup and
 * uncharge "memsw" account.
 */
void mem_cgroup_uncharge_swap(swp_entry_t ent)
{
        struct mem_cgroup *memcg;
        unsigned short id;

        if (!do_swap_account)
                return;

        id = swap_cgroup_record(ent, 0);
        rcu_read_lock();
        memcg = mem_cgroup_lookup(id);
        if (memcg) {
                /*
                 * We uncharge this because swap is freed.
                 * This memcg can be obsolete one. We avoid calling css_tryget
                 */
                if (!mem_cgroup_is_root(memcg))
                        res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
                mem_cgroup_swap_statistics(memcg, false);
                css_put(&memcg->css);
        }
        rcu_read_unlock();
}

/**
 * mem_cgroup_move_swap_account - move swap charge and swap_cgroup's record.
 * @entry: swap entry to be moved
 * @from:  mem_cgroup which the entry is moved from
 * @to:  mem_cgroup which the entry is moved to
 *
 * It succeeds only when the swap_cgroup's record for this entry is the same
 * as the mem_cgroup's id of @from.
 *
 * Returns 0 on success, -EINVAL on failure.
 *
 * The caller must have charged to @to, IOW, called res_counter_charge() about
 * both res and memsw, and called css_get().
 */
static int mem_cgroup_move_swap_account(swp_entry_t entry,
                                struct mem_cgroup *from, struct mem_cgroup *to)
{
        unsigned short old_id, new_id;

        old_id = css_id(&from->css);
        new_id = css_id(&to->css);

        if (swap_cgroup_cmpxchg(entry, old_id, new_id) == old_id) {
                mem_cgroup_swap_statistics(from, false);
                mem_cgroup_swap_statistics(to, true);
                /*
                 * This function is only called from task migration context now.
                 * It postpones res_counter and refcount handling till the end
                 * of task migration(mem_cgroup_clear_mc()) for performance
                 * improvement. But we cannot postpone css_get(to)  because if
                 * the process that has been moved to @to does swap-in, the
                 * refcount of @to might be decreased to 0.
                 *
                 * We are in attach() phase, so the cgroup is guaranteed to be
                 * alive, so we can just call css_get().
                 */
                css_get(&to->css);
                return 0;
        }
        return -EINVAL;
}
#else
static inline int mem_cgroup_move_swap_account(swp_entry_t entry,
                                struct mem_cgroup *from, struct mem_cgroup *to)
{
        return -EINVAL;
}
#endif

/*
 * Before starting migration, account PAGE_SIZE to mem_cgroup that the old
 * page belongs to.
 */
void mem_cgroup_prepare_migration(struct page *page, struct page *newpage,
                                  struct mem_cgroup **memcgp)
{
        struct mem_cgroup *memcg = NULL;
        unsigned int nr_pages = 1;
        struct page_cgroup *pc;
        enum charge_type ctype;

        *memcgp = NULL;

        if (mem_cgroup_disabled())
                return;

        if (PageTransHuge(page))
                nr_pages <<= compound_order(page);

        pc = lookup_page_cgroup(page);
        lock_page_cgroup(pc);
        if (PageCgroupUsed(pc)) {
                memcg = pc->mem_cgroup;
                css_get(&memcg->css);
                /*
                 * At migrating an anonymous page, its mapcount goes down
                 * to 0 and uncharge() will be called. But, even if it's fully
                 * unmapped, migration may fail and this page has to be
                 * charged again. We set MIGRATION flag here and delay uncharge
                 * until end_migration() is called
                 *
                 * Corner Case Thinking
                 * A)
                 * When the old page was mapped as Anon and it's unmap-and-freed
                 * while migration was ongoing.
                 * If unmap finds the old page, uncharge() of it will be delayed
                 * until end_migration(). If unmap finds a new page, it's
                 * uncharged when it make mapcount to be 1->0. If unmap code
                 * finds swap_migration_entry, the new page will not be mapped
                 * and end_migration() will find it(mapcount==0).
                 *
                 * B)
                 * When the old page was mapped but migraion fails, the kernel
                 * remaps it. A charge for it is kept by MIGRATION flag even
                 * if mapcount goes down to 0. We can do remap successfully
                 * without charging it again.
                 *
                 * C)
                 * The "old" page is under lock_page() until the end of
                 * migration, so, the old page itself will not be swapped-out.
                 * If the new page is swapped out before end_migraton, our
                 * hook to usual swap-out path will catch the event.
                 */
                if (PageAnon(page))
                        SetPageCgroupMigration(pc);
        }
        unlock_page_cgroup(pc);
        /*
         * If the page is not charged at this point,
         * we return here.
         */
        if (!memcg)
                return;

        *memcgp = memcg;
        /*
         * We charge new page before it's used/mapped. So, even if unlock_page()
         * is called before end_migration, we can catch all events on this new
         * page. In the case new page is migrated but not remapped, new page's
         * mapcount will be finally 0 and we call uncharge in end_migration().
         */
        if (PageAnon(page))
                ctype = MEM_CGROUP_CHARGE_TYPE_ANON;
        else
                ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
        /*
         * The page is committed to the memcg, but it's not actually
         * charged to the res_counter since we plan on replacing the
         * old one and only one page is going to be left afterwards.
         */
        __mem_cgroup_commit_charge(memcg, newpage, nr_pages, ctype, false);
}

/* remove redundant charge if migration failed*/
void mem_cgroup_end_migration(struct mem_cgroup *memcg,
        struct page *oldpage, struct page *newpage, bool migration_ok)
{
        struct page *used, *unused;
        struct page_cgroup *pc;
        bool anon;

        if (!memcg)
                return;

        if (!migration_ok) {
                used = oldpage;
                unused = newpage;
        } else {
                used = newpage;
                unused = oldpage;
        }
        anon = PageAnon(used);
        __mem_cgroup_uncharge_common(unused,
                                     anon ? MEM_CGROUP_CHARGE_TYPE_ANON
                                     : MEM_CGROUP_CHARGE_TYPE_CACHE,
                                     true);
        css_put(&memcg->css);
        /*
         * We disallowed uncharge of pages under migration because mapcount
         * of the page goes down to zero, temporarly.
         * Clear the flag and check the page should be charged.
         */
        pc = lookup_page_cgroup(oldpage);
        lock_page_cgroup(pc);
        ClearPageCgroupMigration(pc);
        unlock_page_cgroup(pc);

        /*
         * If a page is a file cache, radix-tree replacement is very atomic
         * and we can skip this check. When it was an Anon page, its mapcount
         * goes down to 0. But because we added MIGRATION flage, it's not
         * uncharged yet. There are several case but page->mapcount check
         * and USED bit check in mem_cgroup_uncharge_page() will do enough
         * check. (see prepare_charge() also)
         */
        if (anon)
                mem_cgroup_uncharge_page(used);
}

/*
 * At replace page cache, newpage is not under any memcg but it's on
 * LRU. So, this function doesn't touch res_counter but handles LRU
 * in correct way. Both pages are locked so we cannot race with uncharge.
 */
void mem_cgroup_replace_page_cache(struct page *oldpage,
                                  struct page *newpage)
{
        struct mem_cgroup *memcg = NULL;
        struct page_cgroup *pc;
        enum charge_type type = MEM_CGROUP_CHARGE_TYPE_CACHE;

        if (mem_cgroup_disabled())
                return;

        pc = lookup_page_cgroup(oldpage);
        /* fix accounting on old pages */
        lock_page_cgroup(pc);
        if (PageCgroupUsed(pc)) {
                memcg = pc->mem_cgroup;
                mem_cgroup_charge_statistics(memcg, oldpage, false, -1);
                ClearPageCgroupUsed(pc);
        }
        unlock_page_cgroup(pc);

        /*
         * When called from shmem_replace_page(), in some cases the
         * oldpage has already been charged, and in some cases not.
         */
        if (!memcg)
                return;
        /*
         * Even if newpage->mapping was NULL before starting replacement,
         * the newpage may be on LRU(or pagevec for LRU) already. We lock
         * LRU while we overwrite pc->mem_cgroup.
         */
        __mem_cgroup_commit_charge(memcg, newpage, 1, type, true);
}

#ifdef CONFIG_DEBUG_VM
static struct page_cgroup *lookup_page_cgroup_used(struct page *page)
{
        struct page_cgroup *pc;

        pc = lookup_page_cgroup(page);
        /*
         * Can be NULL while feeding pages into the page allocator for
         * the first time, i.e. during boot or memory hotplug;
         * or when mem_cgroup_disabled().
         */
        if (likely(pc) && PageCgroupUsed(pc))
                return pc;
        return NULL;
}

bool mem_cgroup_bad_page_check(struct page *page)
{
        if (mem_cgroup_disabled())
                return false;

        return lookup_page_cgroup_used(page) != NULL;
}

void mem_cgroup_print_bad_page(struct page *page)
{
        struct page_cgroup *pc;

        pc = lookup_page_cgroup_used(page);
        if (pc) {
                pr_alert("pc:%p pc->flags:%lx pc->mem_cgroup:%p\n",
                         pc, pc->flags, pc->mem_cgroup);
        }
}
#endif

static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
                                unsigned long long val)
{
        int retry_count;
        u64 memswlimit, memlimit;
        int ret = 0;
        int children = mem_cgroup_count_children(memcg);
        u64 curusage, oldusage;
        int enlarge;

        /*
         * For keeping hierarchical_reclaim simple, how long we should retry
         * is depends on callers. We set our retry-count to be function
         * of # of children which we should visit in this loop.
         */
        retry_count = MEM_CGROUP_RECLAIM_RETRIES * children;

        oldusage = res_counter_read_u64(&memcg->res, RES_USAGE);

        enlarge = 0;
        while (retry_count) {
                if (signal_pending(current)) {
                        ret = -EINTR;
                        break;
                }
                /*
                 * Rather than hide all in some function, I do this in
                 * open coded manner. You see what this really does.
                 * We have to guarantee memcg->res.limit <= memcg->memsw.limit.
                 */
                mutex_lock(&set_limit_mutex);
                memswlimit = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
                if (memswlimit < val) {
                        ret = -EINVAL;
                        mutex_unlock(&set_limit_mutex);
                        break;
                }

                memlimit = res_counter_read_u64(&memcg->res, RES_LIMIT);
                if (memlimit < val)
                        enlarge = 1;

                ret = res_counter_set_limit(&memcg->res, val);
                if (!ret) {
                        if (memswlimit == val)
                                memcg->memsw_is_minimum = true;
                        else
                                memcg->memsw_is_minimum = false;
                }
                mutex_unlock(&set_limit_mutex);

                if (!ret)
                        break;

                mem_cgroup_reclaim(memcg, GFP_KERNEL,
                                   MEM_CGROUP_RECLAIM_SHRINK);
                curusage = res_counter_read_u64(&memcg->res, RES_USAGE);
                /* Usage is reduced ? */
                if (curusage >= oldusage)
                        retry_count--;
                else
                        oldusage = curusage;
        }
        if (!ret && enlarge)
                memcg_oom_recover(memcg);

        return ret;
}

static int mem_cgroup_resize_memsw_limit(struct mem_cgroup *memcg,
                                        unsigned long long val)
{
        int retry_count;
        u64 memlimit, memswlimit, oldusage, curusage;
        int children = mem_cgroup_count_children(memcg);
        int ret = -EBUSY;
        int enlarge = 0;

        /* see mem_cgroup_resize_res_limit */
        retry_count = children * MEM_CGROUP_RECLAIM_RETRIES;
        oldusage = res_counter_read_u64(&memcg->memsw, RES_USAGE);
        while (retry_count) {
                if (signal_pending(current)) {
                        ret = -EINTR;
                        break;
                }
                /*
                 * Rather than hide all in some function, I do this in
                 * open coded manner. You see what this really does.
                 * We have to guarantee memcg->res.limit <= memcg->memsw.limit.
                 */
                mutex_lock(&set_limit_mutex);
                memlimit = res_counter_read_u64(&memcg->res, RES_LIMIT);
                if (memlimit > val) {
                        ret = -EINVAL;
                        mutex_unlock(&set_limit_mutex);
                        break;
                }
                memswlimit = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
                if (memswlimit < val)
                        enlarge = 1;
                ret = res_counter_set_limit(&memcg->memsw, val);
                if (!ret) {
                        if (memlimit == val)
                                memcg->memsw_is_minimum = true;
                        else
                                memcg->memsw_is_minimum = false;
                }
                mutex_unlock(&set_limit_mutex);

                if (!ret)
                        break;

                mem_cgroup_reclaim(memcg, GFP_KERNEL,
                                   MEM_CGROUP_RECLAIM_NOSWAP |
                                   MEM_CGROUP_RECLAIM_SHRINK);
                curusage = res_counter_read_u64(&memcg->memsw, RES_USAGE);
                /* Usage is reduced ? */
                if (curusage >= oldusage)
                        retry_count--;
                else
                        oldusage = curusage;
        }
        if (!ret && enlarge)
                memcg_oom_recover(memcg);
        return ret;
}

/**
 * mem_cgroup_force_empty_list - clears LRU of a group
 * @memcg: group to clear
 * @node: NUMA node
 * @zid: zone id
 * @lru: lru to to clear
 *
 * Traverse a specified page_cgroup list and try to drop them all.  This doesn't
 * reclaim the pages page themselves - pages are moved to the parent (or root)
 * group.
 */
static void mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
                                int node, int zid, enum lru_list lru)
{
        struct lruvec *lruvec;
        unsigned long flags;
        struct list_head *list;
        struct page *busy;
        struct zone *zone;

        zone = &NODE_DATA(node)->node_zones[zid];
        lruvec = mem_cgroup_zone_lruvec(zone, memcg);
        list = &lruvec->lists[lru];

        busy = NULL;
        do {
                struct page_cgroup *pc;
                struct page *page;

                spin_lock_irqsave(&zone->lru_lock, flags);
                if (list_empty(list)) {
                        spin_unlock_irqrestore(&zone->lru_lock, flags);
                        break;
                }
                page = list_entry(list->prev, struct page, lru);
                if (busy == page) {
                        list_move(&page->lru, list);
                        busy = NULL;
                        spin_unlock_irqrestore(&zone->lru_lock, flags);
                        continue;
                }
                spin_unlock_irqrestore(&zone->lru_lock, flags);

                pc = lookup_page_cgroup(page);

                if (mem_cgroup_move_parent(page, pc, memcg)) {
                        /* found lock contention or "pc" is obsolete. */
                        busy = page;
                        cond_resched();
                } else
                        busy = NULL;
        } while (!list_empty(list));
}

/*
 * make mem_cgroup's charge to be 0 if there is no task by moving
 * all the charges and pages to the parent.
 * This enables deleting this mem_cgroup.
 *
 * Caller is responsible for holding css reference on the memcg.
 */
static void mem_cgroup_reparent_charges(struct mem_cgroup *memcg)
{
        int node, zid;
        u64 usage;

        do {
                /* This is for making all *used* pages to be on LRU. */
                lru_add_drain_all();
                drain_all_stock_sync(memcg);
                mem_cgroup_start_move(memcg);
                for_each_node_state(node, N_MEMORY) {
                        for (zid = 0; zid < MAX_NR_ZONES; zid++) {
                                enum lru_list lru;
                                for_each_lru(lru) {
                                        mem_cgroup_force_empty_list(memcg,
                                                        node, zid, lru);
                                }
                        }
                }
                mem_cgroup_end_move(memcg);
                memcg_oom_recover(memcg);
                cond_resched();

                /*
                 * Kernel memory may not necessarily be trackable to a specific
                 * process. So they are not migrated, and therefore we can't
                 * expect their value to drop to 0 here.
                 * Having res filled up with kmem only is enough.
                 *
                 * This is a safety check because mem_cgroup_force_empty_list
                 * could have raced with mem_cgroup_replace_page_cache callers
                 * so the lru seemed empty but the page could have been added
                 * right after the check. RES_USAGE should be safe as we always
                 * charge before adding to the LRU.
                 */
                usage = res_counter_read_u64(&memcg->res, RES_USAGE) -
                        res_counter_read_u64(&memcg->kmem, RES_USAGE);
        } while (usage > 0);
}

/*
 * This mainly exists for tests during the setting of set of use_hierarchy.
 * Since this is the very setting we are changing, the current hierarchy value
 * is meaningless
 */
static inline bool __memcg_has_children(struct mem_cgroup *memcg)
{
        struct cgroup_subsys_state *pos;

        /* bounce at first found */
        css_for_each_child(pos, &memcg->css)
                return true;
        return false;
}

/*
 * Must be called with memcg_create_mutex held, unless the cgroup is guaranteed
 * to be already dead (as in mem_cgroup_force_empty, for instance).  This is
 * from mem_cgroup_count_children(), in the sense that we don't really care how
 * many children we have; we only need to know if we have any.  It also counts
 * any memcg without hierarchy as infertile.
 */
static inline bool memcg_has_children(struct mem_cgroup *memcg)
{
        return memcg->use_hierarchy && __memcg_has_children(memcg);
}

/*
 * Reclaims as many pages from the given memcg as possible and moves
 * the rest to the parent.
 *
 * Caller is responsible for holding css reference for memcg.
 */
static int mem_cgroup_force_empty(struct mem_cgroup *memcg)
{
        int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
        struct cgroup *cgrp = memcg->css.cgroup;

        /* returns EBUSY if there is a task or if we come here twice. */
        if (cgroup_task_count(cgrp) || !list_empty(&cgrp->children))
                return -EBUSY;

        /* we call try-to-free pages for make this cgroup empty */
        lru_add_drain_all();
        /* try to free all pages in this cgroup */
        while (nr_retries && res_counter_read_u64(&memcg->res, RES_USAGE) > 0) {
                int progress;

                if (signal_pending(current))
                        return -EINTR;

                progress = try_to_free_mem_cgroup_pages(memcg, GFP_KERNEL,
                                                false);
                if (!progress) {
                        nr_retries--;
                        /* maybe some writeback is necessary */
                        congestion_wait(BLK_RW_ASYNC, HZ/10);
                }

        }
        lru_add_drain();
        mem_cgroup_reparent_charges(memcg);

        return 0;
}

static int mem_cgroup_force_empty_write(struct cgroup_subsys_state *css,
                                        unsigned int event)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);

        if (mem_cgroup_is_root(memcg))
                return -EINVAL;
        return mem_cgroup_force_empty(memcg);
}

static u64 mem_cgroup_hierarchy_read(struct cgroup_subsys_state *css,
                                     struct cftype *cft)
{
        return mem_cgroup_from_css(css)->use_hierarchy;
}

static int mem_cgroup_hierarchy_write(struct cgroup_subsys_state *css,
                                      struct cftype *cft, u64 val)
{
        int retval = 0;
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
        struct mem_cgroup *parent_memcg = mem_cgroup_from_css(css_parent(&memcg->css));

        mutex_lock(&memcg_create_mutex);

        if (memcg->use_hierarchy == val)
                goto out;

        /*
         * If parent's use_hierarchy is set, we can't make any modifications
         * in the child subtrees. If it is unset, then the change can
         * occur, provided the current cgroup has no children.
         *
         * For the root cgroup, parent_mem is NULL, we allow value to be
         * set if there are no children.
         */
        if ((!parent_memcg || !parent_memcg->use_hierarchy) &&
                                (val == 1 || val == 0)) {
                if (!__memcg_has_children(memcg))
                        memcg->use_hierarchy = val;
                else
                        retval = -EBUSY;
        } else
                retval = -EINVAL;

out:
        mutex_unlock(&memcg_create_mutex);

        return retval;
}


static unsigned long mem_cgroup_recursive_stat(struct mem_cgroup *memcg,
                                               enum mem_cgroup_stat_index idx)
{
        struct mem_cgroup *iter;
        long val = 0;

        /* Per-cpu values can be negative, use a signed accumulator */
        for_each_mem_cgroup_tree(iter, memcg)
                val += mem_cgroup_read_stat(iter, idx);

        if (val < 0) /* race ? */
                val = 0;
        return val;
}

static inline u64 mem_cgroup_usage(struct mem_cgroup *memcg, bool swap)
{
        u64 val;

        if (!mem_cgroup_is_root(memcg)) {
                if (!swap)
                        return res_counter_read_u64(&memcg->res, RES_USAGE);
                else
                        return res_counter_read_u64(&memcg->memsw, RES_USAGE);
        }

        /*
         * Transparent hugepages are still accounted for in MEM_CGROUP_STAT_RSS
         * as well as in MEM_CGROUP_STAT_RSS_HUGE.
         */
        val = mem_cgroup_recursive_stat(memcg, MEM_CGROUP_STAT_CACHE);
        val += mem_cgroup_recursive_stat(memcg, MEM_CGROUP_STAT_RSS);

        if (swap)
                val += mem_cgroup_recursive_stat(memcg, MEM_CGROUP_STAT_SWAP);

        return val << PAGE_SHIFT;
}

static ssize_t mem_cgroup_read(struct cgroup_subsys_state *css,
                               struct cftype *cft, struct file *file,
                               char __user *buf, size_t nbytes, loff_t *ppos)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
        char str[64];
        u64 val;
        int name, len;
        enum res_type type;

        type = MEMFILE_TYPE(cft->private);
        name = MEMFILE_ATTR(cft->private);

        switch (type) {
        case _MEM:
                if (name == RES_USAGE)
                        val = mem_cgroup_usage(memcg, false);
                else
                        val = res_counter_read_u64(&memcg->res, name);
                break;
        case _MEMSWAP:
                if (name == RES_USAGE)
                        val = mem_cgroup_usage(memcg, true);
                else
                        val = res_counter_read_u64(&memcg->memsw, name);
                break;
        case _KMEM:
                val = res_counter_read_u64(&memcg->kmem, name);
                break;
        default:
                BUG();
        }

        len = scnprintf(str, sizeof(str), "%llu\n", (unsigned long long)val);
        return simple_read_from_buffer(buf, nbytes, ppos, str, len);
}

static int memcg_update_kmem_limit(struct cgroup_subsys_state *css, u64 val)
{
        int ret = -EINVAL;
#ifdef CONFIG_MEMCG_KMEM
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
        /*
         * For simplicity, we won't allow this to be disabled.  It also can't
         * be changed if the cgroup has children already, or if tasks had
         * already joined.
         *
         * If tasks join before we set the limit, a person looking at
         * kmem.usage_in_bytes will have no way to determine when it took
         * place, which makes the value quite meaningless.
         *
         * After it first became limited, changes in the value of the limit are
         * of course permitted.
         */
        mutex_lock(&memcg_create_mutex);
        mutex_lock(&set_limit_mutex);
        if (!memcg->kmem_account_flags && val != RESOURCE_MAX) {
                if (cgroup_task_count(css->cgroup) || memcg_has_children(memcg)) {
                        ret = -EBUSY;
                        goto out;
                }
                ret = res_counter_set_limit(&memcg->kmem, val);
                VM_BUG_ON(ret);

                ret = memcg_update_cache_sizes(memcg);
                if (ret) {
                        res_counter_set_limit(&memcg->kmem, RESOURCE_MAX);
                        goto out;
                }
                static_key_slow_inc(&memcg_kmem_enabled_key);
                /*
                 * setting the active bit after the inc will guarantee no one
                 * starts accounting before all call sites are patched
                 */
                memcg_kmem_set_active(memcg);
        } else
                ret = res_counter_set_limit(&memcg->kmem, val);
out:
        mutex_unlock(&set_limit_mutex);
        mutex_unlock(&memcg_create_mutex);
#endif
        return ret;
}

#ifdef CONFIG_MEMCG_KMEM
static int memcg_propagate_kmem(struct mem_cgroup *memcg)
{
        int ret = 0;
        struct mem_cgroup *parent = parent_mem_cgroup(memcg);
        if (!parent)
                goto out;

        memcg->kmem_account_flags = parent->kmem_account_flags;
        /*
         * When that happen, we need to disable the static branch only on those
         * memcgs that enabled it. To achieve this, we would be forced to
         * complicate the code by keeping track of which memcgs were the ones
         * that actually enabled limits, and which ones got it from its
         * parents.
         *
         * It is a lot simpler just to do static_key_slow_inc() on every child
         * that is accounted.
         */
        if (!memcg_kmem_is_active(memcg))
                goto out;

        /*
         * __mem_cgroup_free() will issue static_key_slow_dec() because this
         * memcg is active already. If the later initialization fails then the
         * cgroup core triggers the cleanup so we do not have to do it here.
         */
        static_key_slow_inc(&memcg_kmem_enabled_key);

        mutex_lock(&set_limit_mutex);
        memcg_stop_kmem_account();
        ret = memcg_update_cache_sizes(memcg);
        memcg_resume_kmem_account();
        mutex_unlock(&set_limit_mutex);
out:
        return ret;
}
#endif /* CONFIG_MEMCG_KMEM */

/*
 * The user of this function is...
 * RES_LIMIT.
 */
static int mem_cgroup_write(struct cgroup_subsys_state *css, struct cftype *cft,
                            const char *buffer)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
        enum res_type type;
        int name;
        unsigned long long val;
        int ret;

        type = MEMFILE_TYPE(cft->private);
        name = MEMFILE_ATTR(cft->private);

        switch (name) {
        case RES_LIMIT:
                if (mem_cgroup_is_root(memcg)) { /* Can't set limit on root */
                        ret = -EINVAL;
                        break;
                }
                /* This function does all necessary parse...reuse it */
                ret = res_counter_memparse_write_strategy(buffer, &val);
                if (ret)
                        break;
                if (type == _MEM)
                        ret = mem_cgroup_resize_limit(memcg, val);
                else if (type == _MEMSWAP)
                        ret = mem_cgroup_resize_memsw_limit(memcg, val);
                else if (type == _KMEM)
                        ret = memcg_update_kmem_limit(css, val);
                else
                        return -EINVAL;
                break;
        case RES_SOFT_LIMIT:
                ret = res_counter_memparse_write_strategy(buffer, &val);
                if (ret)
                        break;
                /*
                 * For memsw, soft limits are hard to implement in terms
                 * of semantics, for now, we support soft limits for
                 * control without swap
                 */
                if (type == _MEM)
                        ret = res_counter_set_soft_limit(&memcg->res, val);
                else
                        ret = -EINVAL;
                break;
        default:
                ret = -EINVAL; /* should be BUG() ? */
                break;
        }
        return ret;
}

static void memcg_get_hierarchical_limit(struct mem_cgroup *memcg,
                unsigned long long *mem_limit, unsigned long long *memsw_limit)
{
        unsigned long long min_limit, min_memsw_limit, tmp;

        min_limit = res_counter_read_u64(&memcg->res, RES_LIMIT);
        min_memsw_limit = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
        if (!memcg->use_hierarchy)
                goto out;

        while (css_parent(&memcg->css)) {
                memcg = mem_cgroup_from_css(css_parent(&memcg->css));
                if (!memcg->use_hierarchy)
                        break;
                tmp = res_counter_read_u64(&memcg->res, RES_LIMIT);
                min_limit = min(min_limit, tmp);
                tmp = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
                min_memsw_limit = min(min_memsw_limit, tmp);
        }
out:
        *mem_limit = min_limit;
        *memsw_limit = min_memsw_limit;
}

static int mem_cgroup_reset(struct cgroup_subsys_state *css, unsigned int event)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
        int name;
        enum res_type type;

        type = MEMFILE_TYPE(event);
        name = MEMFILE_ATTR(event);

        switch (name) {
        case RES_MAX_USAGE:
                if (type == _MEM)
                        res_counter_reset_max(&memcg->res);
                else if (type == _MEMSWAP)
                        res_counter_reset_max(&memcg->memsw);
                else if (type == _KMEM)
                        res_counter_reset_max(&memcg->kmem);
                else
                        return -EINVAL;
                break;
        case RES_FAILCNT:
                if (type == _MEM)
                        res_counter_reset_failcnt(&memcg->res);
                else if (type == _MEMSWAP)
                        res_counter_reset_failcnt(&memcg->memsw);
                else if (type == _KMEM)
                        res_counter_reset_failcnt(&memcg->kmem);
                else
                        return -EINVAL;
                break;
        }

        return 0;
}

static u64 mem_cgroup_move_charge_read(struct cgroup_subsys_state *css,
                                        struct cftype *cft)
{
        return mem_cgroup_from_css(css)->move_charge_at_immigrate;
}

#ifdef CONFIG_MMU
static int mem_cgroup_move_charge_write(struct cgroup_subsys_state *css,
                                        struct cftype *cft, u64 val)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);

        if (val >= (1 << NR_MOVE_TYPE))
                return -EINVAL;

        /*
         * No kind of locking is needed in here, because ->can_attach() will
         * check this value once in the beginning of the process, and then carry
         * on with stale data. This means that changes to this value will only
         * affect task migrations starting after the change.
         */
        memcg->move_charge_at_immigrate = val;
        return 0;
}
#else
static int mem_cgroup_move_charge_write(struct cgroup_subsys_state *css,
                                        struct cftype *cft, u64 val)
{
        return -ENOSYS;
}
#endif

#ifdef CONFIG_NUMA
static int memcg_numa_stat_show(struct cgroup_subsys_state *css,
                                struct cftype *cft, struct seq_file *m)
{
        int nid;
        unsigned long total_nr, file_nr, anon_nr, unevictable_nr;
        unsigned long node_nr;
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);

        total_nr = mem_cgroup_nr_lru_pages(memcg, LRU_ALL);
        seq_printf(m, "total=%lu", total_nr);
        for_each_node_state(nid, N_MEMORY) {
                node_nr = mem_cgroup_node_nr_lru_pages(memcg, nid, LRU_ALL);
                seq_printf(m, " N%d=%lu", nid, node_nr);
        }
        seq_putc(m, '\n');

        file_nr = mem_cgroup_nr_lru_pages(memcg, LRU_ALL_FILE);
        seq_printf(m, "file=%lu", file_nr);
        for_each_node_state(nid, N_MEMORY) {
                node_nr = mem_cgroup_node_nr_lru_pages(memcg, nid,
                                LRU_ALL_FILE);
                seq_printf(m, " N%d=%lu", nid, node_nr);
        }
        seq_putc(m, '\n');

        anon_nr = mem_cgroup_nr_lru_pages(memcg, LRU_ALL_ANON);
        seq_printf(m, "anon=%lu", anon_nr);
        for_each_node_state(nid, N_MEMORY) {
                node_nr = mem_cgroup_node_nr_lru_pages(memcg, nid,
                                LRU_ALL_ANON);
                seq_printf(m, " N%d=%lu", nid, node_nr);
        }
        seq_putc(m, '\n');

        unevictable_nr = mem_cgroup_nr_lru_pages(memcg, BIT(LRU_UNEVICTABLE));
        seq_printf(m, "unevictable=%lu", unevictable_nr);
        for_each_node_state(nid, N_MEMORY) {
                node_nr = mem_cgroup_node_nr_lru_pages(memcg, nid,
                                BIT(LRU_UNEVICTABLE));
                seq_printf(m, " N%d=%lu", nid, node_nr);
        }
        seq_putc(m, '\n');
        return 0;
}
#endif /* CONFIG_NUMA */

static inline void mem_cgroup_lru_names_not_uptodate(void)
{
        BUILD_BUG_ON(ARRAY_SIZE(mem_cgroup_lru_names) != NR_LRU_LISTS);
}

static int memcg_stat_show(struct cgroup_subsys_state *css, struct cftype *cft,
                                 struct seq_file *m)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
        struct mem_cgroup *mi;
        unsigned int i;

        for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) {
                if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account)
                        continue;
                seq_printf(m, "%s %ld\n", mem_cgroup_stat_names[i],
                           mem_cgroup_read_stat(memcg, i) * PAGE_SIZE);
        }

        for (i = 0; i < MEM_CGROUP_EVENTS_NSTATS; i++)
                seq_printf(m, "%s %lu\n", mem_cgroup_events_names[i],
                           mem_cgroup_read_events(memcg, i));

        for (i = 0; i < NR_LRU_LISTS; i++)
                seq_printf(m, "%s %lu\n", mem_cgroup_lru_names[i],
                           mem_cgroup_nr_lru_pages(memcg, BIT(i)) * PAGE_SIZE);

        /* Hierarchical information */
        {
                unsigned long long limit, memsw_limit;
                memcg_get_hierarchical_limit(memcg, &limit, &memsw_limit);
                seq_printf(m, "hierarchical_memory_limit %llu\n", limit);
                if (do_swap_account)
                        seq_printf(m, "hierarchical_memsw_limit %llu\n",
                                   memsw_limit);
        }

        for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) {
                long long val = 0;

                if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account)
                        continue;
                for_each_mem_cgroup_tree(mi, memcg)
                        val += mem_cgroup_read_stat(mi, i) * PAGE_SIZE;
                seq_printf(m, "total_%s %lld\n", mem_cgroup_stat_names[i], val);
        }

        for (i = 0; i < MEM_CGROUP_EVENTS_NSTATS; i++) {
                unsigned long long val = 0;

                for_each_mem_cgroup_tree(mi, memcg)
                        val += mem_cgroup_read_events(mi, i);
                seq_printf(m, "total_%s %llu\n",
                           mem_cgroup_events_names[i], val);
        }

        for (i = 0; i < NR_LRU_LISTS; i++) {
                unsigned long long val = 0;

                for_each_mem_cgroup_tree(mi, memcg)
                        val += mem_cgroup_nr_lru_pages(mi, BIT(i)) * PAGE_SIZE;
                seq_printf(m, "total_%s %llu\n", mem_cgroup_lru_names[i], val);
        }

#ifdef CONFIG_DEBUG_VM
        {
                int nid, zid;
                struct mem_cgroup_per_zone *mz;
                struct zone_reclaim_stat *rstat;
                unsigned long recent_rotated[2] = {0, 0};
                unsigned long recent_scanned[2] = {0, 0};

                for_each_online_node(nid)
                        for (zid = 0; zid < MAX_NR_ZONES; zid++) {
                                mz = mem_cgroup_zoneinfo(memcg, nid, zid);
                                rstat = &mz->lruvec.reclaim_stat;

                                recent_rotated[0] += rstat->recent_rotated[0];
                                recent_rotated[1] += rstat->recent_rotated[1];
                                recent_scanned[0] += rstat->recent_scanned[0];
                                recent_scanned[1] += rstat->recent_scanned[1];
                        }
                seq_printf(m, "recent_rotated_anon %lu\n", recent_rotated[0]);
                seq_printf(m, "recent_rotated_file %lu\n", recent_rotated[1]);
                seq_printf(m, "recent_scanned_anon %lu\n", recent_scanned[0]);
                seq_printf(m, "recent_scanned_file %lu\n", recent_scanned[1]);
        }
#endif

        return 0;
}

static u64 mem_cgroup_swappiness_read(struct cgroup_subsys_state *css,
                                      struct cftype *cft)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);

        return mem_cgroup_swappiness(memcg);
}

static int mem_cgroup_swappiness_write(struct cgroup_subsys_state *css,
                                       struct cftype *cft, u64 val)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
        struct mem_cgroup *parent = mem_cgroup_from_css(css_parent(&memcg->css));

        if (val > 100 || !parent)
                return -EINVAL;

        mutex_lock(&memcg_create_mutex);

        /* If under hierarchy, only empty-root can set this value */
        if ((parent->use_hierarchy) || memcg_has_children(memcg)) {
                mutex_unlock(&memcg_create_mutex);
                return -EINVAL;
        }

        memcg->swappiness = val;

        mutex_unlock(&memcg_create_mutex);

        return 0;
}

static void __mem_cgroup_threshold(struct mem_cgroup *memcg, bool swap)
{
        struct mem_cgroup_threshold_ary *t;
        u64 usage;
        int i;

        rcu_read_lock();
        if (!swap)
                t = rcu_dereference(memcg->thresholds.primary);
        else
                t = rcu_dereference(memcg->memsw_thresholds.primary);

        if (!t)
                goto unlock;

        usage = mem_cgroup_usage(memcg, swap);

        /*
         * current_threshold points to threshold just below or equal to usage.
         * If it's not true, a threshold was crossed after last
         * call of __mem_cgroup_threshold().
         */
        i = t->current_threshold;

        /*
         * Iterate backward over array of thresholds starting from
         * current_threshold and check if a threshold is crossed.
         * If none of thresholds below usage is crossed, we read
         * only one element of the array here.
         */
        for (; i >= 0 && unlikely(t->entries[i].threshold > usage); i--)
                eventfd_signal(t->entries[i].eventfd, 1);

        /* i = current_threshold + 1 */
        i++;

        /*
         * Iterate forward over array of thresholds starting from
         * current_threshold+1 and check if a threshold is crossed.
         * If none of thresholds above usage is crossed, we read
         * only one element of the array here.
         */
        for (; i < t->size && unlikely(t->entries[i].threshold <= usage); i++)
                eventfd_signal(t->entries[i].eventfd, 1);

        /* Update current_threshold */
        t->current_threshold = i - 1;
unlock:
        rcu_read_unlock();
}

static void mem_cgroup_threshold(struct mem_cgroup *memcg)
{
        while (memcg) {
                __mem_cgroup_threshold(memcg, false);
                if (do_swap_account)
                        __mem_cgroup_threshold(memcg, true);

                memcg = parent_mem_cgroup(memcg);
        }
}

static int compare_thresholds(const void *a, const void *b)
{
        const struct mem_cgroup_threshold *_a = a;
        const struct mem_cgroup_threshold *_b = b;

        if (_a->threshold > _b->threshold)
                return 1;

        if (_a->threshold < _b->threshold)
                return -1;

        return 0;
}

static int mem_cgroup_oom_notify_cb(struct mem_cgroup *memcg)
{
        struct mem_cgroup_eventfd_list *ev;

        list_for_each_entry(ev, &memcg->oom_notify, list)
                eventfd_signal(ev->eventfd, 1);
        return 0;
}

static void mem_cgroup_oom_notify(struct mem_cgroup *memcg)
{
        struct mem_cgroup *iter;

        for_each_mem_cgroup_tree(iter, memcg)
                mem_cgroup_oom_notify_cb(iter);
}

static int mem_cgroup_usage_register_event(struct cgroup_subsys_state *css,
        struct cftype *cft, struct eventfd_ctx *eventfd, const char *args)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
        struct mem_cgroup_thresholds *thresholds;
        struct mem_cgroup_threshold_ary *new;
        enum res_type type = MEMFILE_TYPE(cft->private);
        u64 threshold, usage;
        int i, size, ret;

        ret = res_counter_memparse_write_strategy(args, &threshold);
        if (ret)
                return ret;

        mutex_lock(&memcg->thresholds_lock);

        if (type == _MEM)
                thresholds = &memcg->thresholds;
        else if (type == _MEMSWAP)
                thresholds = &memcg->memsw_thresholds;
        else
                BUG();

        usage = mem_cgroup_usage(memcg, type == _MEMSWAP);

        /* Check if a threshold crossed before adding a new one */
        if (thresholds->primary)
                __mem_cgroup_threshold(memcg, type == _MEMSWAP);

        size = thresholds->primary ? thresholds->primary->size + 1 : 1;

        /* Allocate memory for new array of thresholds */
        new = kmalloc(sizeof(*new) + size * sizeof(struct mem_cgroup_threshold),
                        GFP_KERNEL);
        if (!new) {
                ret = -ENOMEM;
                goto unlock;
        }
        new->size = size;

        /* Copy thresholds (if any) to new array */
        if (thresholds->primary) {
                memcpy(new->entries, thresholds->primary->entries, (size - 1) *
                                sizeof(struct mem_cgroup_threshold));
        }

        /* Add new threshold */
        new->entries[size - 1].eventfd = eventfd;
        new->entries[size - 1].threshold = threshold;

        /* Sort thresholds. Registering of new threshold isn't time-critical */
        sort(new->entries, size, sizeof(struct mem_cgroup_threshold),
                        compare_thresholds, NULL);

        /* Find current threshold */
        new->current_threshold = -1;
        for (i = 0; i < size; i++) {
                if (new->entries[i].threshold <= usage) {
                        /*
                         * new->current_threshold will not be used until
                         * rcu_assign_pointer(), so it's safe to increment
                         * it here.
                         */
                        ++new->current_threshold;
                } else
                        break;
        }

        /* Free old spare buffer and save old primary buffer as spare */
        kfree(thresholds->spare);
        thresholds->spare = thresholds->primary;

        rcu_assign_pointer(thresholds->primary, new);

        /* To be sure that nobody uses thresholds */
        synchronize_rcu();

unlock:
        mutex_unlock(&memcg->thresholds_lock);

        return ret;
}

static void mem_cgroup_usage_unregister_event(struct cgroup_subsys_state *css,
        struct cftype *cft, struct eventfd_ctx *eventfd)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
        struct mem_cgroup_thresholds *thresholds;
        struct mem_cgroup_threshold_ary *new;
        enum res_type type = MEMFILE_TYPE(cft->private);
        u64 usage;
        int i, j, size;

        mutex_lock(&memcg->thresholds_lock);
        if (type == _MEM)
                thresholds = &memcg->thresholds;
        else if (type == _MEMSWAP)
                thresholds = &memcg->memsw_thresholds;
        else
                BUG();

        if (!thresholds->primary)
                goto unlock;

        usage = mem_cgroup_usage(memcg, type == _MEMSWAP);

        /* Check if a threshold crossed before removing */
        __mem_cgroup_threshold(memcg, type == _MEMSWAP);

        /* Calculate new number of threshold */
        size = 0;
        for (i = 0; i < thresholds->primary->size; i++) {
                if (thresholds->primary->entries[i].eventfd != eventfd)
                        size++;
        }

        new = thresholds->spare;

        /* Set thresholds array to NULL if we don't have thresholds */
        if (!size) {
                kfree(new);
                new = NULL;
                goto swap_buffers;
        }

        new->size = size;

        /* Copy thresholds and find current threshold */
        new->current_threshold = -1;
        for (i = 0, j = 0; i < thresholds->primary->size; i++) {
                if (thresholds->primary->entries[i].eventfd == eventfd)
                        continue;

                new->entries[j] = thresholds->primary->entries[i];
                if (new->entries[j].threshold <= usage) {
                        /*
                         * new->current_threshold will not be used
                         * until rcu_assign_pointer(), so it's safe to increment
                         * it here.
                         */
                        ++new->current_threshold;
                }
                j++;
        }

swap_buffers:
        /* Swap primary and spare array */
        thresholds->spare = thresholds->primary;
        /* If all events are unregistered, free the spare array */
        if (!new) {
                kfree(thresholds->spare);
                thresholds->spare = NULL;
        }

        rcu_assign_pointer(thresholds->primary, new);

        /* To be sure that nobody uses thresholds */
        synchronize_rcu();
unlock:
        mutex_unlock(&memcg->thresholds_lock);
}

static int mem_cgroup_oom_register_event(struct cgroup_subsys_state *css,
        struct cftype *cft, struct eventfd_ctx *eventfd, const char *args)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
        struct mem_cgroup_eventfd_list *event;
        enum res_type type = MEMFILE_TYPE(cft->private);

        BUG_ON(type != _OOM_TYPE);
        event = kmalloc(sizeof(*event), GFP_KERNEL);
        if (!event)
                return -ENOMEM;

        spin_lock(&memcg_oom_lock);

        event->eventfd = eventfd;
        list_add(&event->list, &memcg->oom_notify);

        /* already in OOM ? */
        if (atomic_read(&memcg->under_oom))
                eventfd_signal(eventfd, 1);
        spin_unlock(&memcg_oom_lock);

        return 0;
}

static void mem_cgroup_oom_unregister_event(struct cgroup_subsys_state *css,
        struct cftype *cft, struct eventfd_ctx *eventfd)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
        struct mem_cgroup_eventfd_list *ev, *tmp;
        enum res_type type = MEMFILE_TYPE(cft->private);

        BUG_ON(type != _OOM_TYPE);

        spin_lock(&memcg_oom_lock);

        list_for_each_entry_safe(ev, tmp, &memcg->oom_notify, list) {
                if (ev->eventfd == eventfd) {
                        list_del(&ev->list);
                        kfree(ev);
                }
        }

        spin_unlock(&memcg_oom_lock);
}

static int mem_cgroup_oom_control_read(struct cgroup_subsys_state *css,
        struct cftype *cft,  struct cgroup_map_cb *cb)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);

        cb->fill(cb, "oom_kill_disable", memcg->oom_kill_disable);

        if (atomic_read(&memcg->under_oom))
                cb->fill(cb, "under_oom", 1);
        else
                cb->fill(cb, "under_oom", 0);
        return 0;
}

static int mem_cgroup_oom_control_write(struct cgroup_subsys_state *css,
        struct cftype *cft, u64 val)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
        struct mem_cgroup *parent = mem_cgroup_from_css(css_parent(&memcg->css));

        /* cannot set to root cgroup and only 0 and 1 are allowed */
        if (!parent || !((val == 0) || (val == 1)))
                return -EINVAL;

        mutex_lock(&memcg_create_mutex);
        /* oom-kill-disable is a flag for subhierarchy. */
        if ((parent->use_hierarchy) || memcg_has_children(memcg)) {
                mutex_unlock(&memcg_create_mutex);
                return -EINVAL;
        }
        memcg->oom_kill_disable = val;
        if (!val)
                memcg_oom_recover(memcg);
        mutex_unlock(&memcg_create_mutex);
        return 0;
}

#ifdef CONFIG_MEMCG_KMEM
static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
{
        int ret;

        memcg->kmemcg_id = -1;
        ret = memcg_propagate_kmem(memcg);
        if (ret)
                return ret;

        return mem_cgroup_sockets_init(memcg, ss);
}

static void memcg_destroy_kmem(struct mem_cgroup *memcg)
{
        mem_cgroup_sockets_destroy(memcg);
}

static void kmem_cgroup_css_offline(struct mem_cgroup *memcg)
{
        if (!memcg_kmem_is_active(memcg))
                return;

        /*
         * kmem charges can outlive the cgroup. In the case of slab
         * pages, for instance, a page contain objects from various
         * processes. As we prevent from taking a reference for every
         * such allocation we have to be careful when doing uncharge
         * (see memcg_uncharge_kmem) and here during offlining.
         *
         * The idea is that that only the _last_ uncharge which sees
         * the dead memcg will drop the last reference. An additional
         * reference is taken here before the group is marked dead
         * which is then paired with css_put during uncharge resp. here.
         *
         * Although this might sound strange as this path is called from
         * css_offline() when the referencemight have dropped down to 0
         * and shouldn't be incremented anymore (css_tryget would fail)
         * we do not have other options because of the kmem allocations
         * lifetime.
         */
        css_get(&memcg->css);

        memcg_kmem_mark_dead(memcg);

        if (res_counter_read_u64(&memcg->kmem, RES_USAGE) != 0)
                return;

        if (memcg_kmem_test_and_clear_dead(memcg))
                css_put(&memcg->css);
}
#else
static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
{
        return 0;
}

static void memcg_destroy_kmem(struct mem_cgroup *memcg)
{
}

static void kmem_cgroup_css_offline(struct mem_cgroup *memcg)
{
}
#endif

static struct cftype mem_cgroup_files[] = {
        {
                .name = "usage_in_bytes",
                .private = MEMFILE_PRIVATE(_MEM, RES_USAGE),
                .read = mem_cgroup_read,
                .register_event = mem_cgroup_usage_register_event,
                .unregister_event = mem_cgroup_usage_unregister_event,
        },
        {
                .name = "max_usage_in_bytes",
                .private = MEMFILE_PRIVATE(_MEM, RES_MAX_USAGE),
                .trigger = mem_cgroup_reset,
                .read = mem_cgroup_read,
        },
        {
                .name = "limit_in_bytes",
                .private = MEMFILE_PRIVATE(_MEM, RES_LIMIT),
                .write_string = mem_cgroup_write,
                .read = mem_cgroup_read,
        },
        {
                .name = "soft_limit_in_bytes",
                .private = MEMFILE_PRIVATE(_MEM, RES_SOFT_LIMIT),
                .write_string = mem_cgroup_write,
                .read = mem_cgroup_read,
        },
        {
                .name = "failcnt",
                .private = MEMFILE_PRIVATE(_MEM, RES_FAILCNT),
                .trigger = mem_cgroup_reset,
                .read = mem_cgroup_read,
        },
        {
                .name = "stat",
                .read_seq_string = memcg_stat_show,
        },
        {
                .name = "force_empty",
                .trigger = mem_cgroup_force_empty_write,
        },
        {
                .name = "use_hierarchy",
                .flags = CFTYPE_INSANE,
                .write_u64 = mem_cgroup_hierarchy_write,
                .read_u64 = mem_cgroup_hierarchy_read,
        },
        {
                .name = "swappiness",
                .read_u64 = mem_cgroup_swappiness_read,
                .write_u64 = mem_cgroup_swappiness_write,
        },
        {
                .name = "move_charge_at_immigrate",
                .read_u64 = mem_cgroup_move_charge_read,
                .write_u64 = mem_cgroup_move_charge_write,
        },
        {
                .name = "oom_control",
                .read_map = mem_cgroup_oom_control_read,
                .write_u64 = mem_cgroup_oom_control_write,
                .register_event = mem_cgroup_oom_register_event,
                .unregister_event = mem_cgroup_oom_unregister_event,
                .private = MEMFILE_PRIVATE(_OOM_TYPE, OOM_CONTROL),
        },
        {
                .name = "pressure_level",
                .register_event = vmpressure_register_event,
                .unregister_event = vmpressure_unregister_event,
        },
#ifdef CONFIG_NUMA
        {
                .name = "numa_stat",
                .read_seq_string = memcg_numa_stat_show,
        },
#endif
#ifdef CONFIG_MEMCG_KMEM
        {
                .name = "kmem.limit_in_bytes",
                .private = MEMFILE_PRIVATE(_KMEM, RES_LIMIT),
                .write_string = mem_cgroup_write,
                .read = mem_cgroup_read,
        },
        {
                .name = "kmem.usage_in_bytes",
                .private = MEMFILE_PRIVATE(_KMEM, RES_USAGE),
                .read = mem_cgroup_read,
        },
        {
                .name = "kmem.failcnt",
                .private = MEMFILE_PRIVATE(_KMEM, RES_FAILCNT),
                .trigger = mem_cgroup_reset,
                .read = mem_cgroup_read,
        },
        {
                .name = "kmem.max_usage_in_bytes",
                .private = MEMFILE_PRIVATE(_KMEM, RES_MAX_USAGE),
                .trigger = mem_cgroup_reset,
                .read = mem_cgroup_read,
        },
#ifdef CONFIG_SLABINFO
        {
                .name = "kmem.slabinfo",
                .read_seq_string = mem_cgroup_slabinfo_read,
        },
#endif
#endif
        { },    /* terminate */
};

#ifdef CONFIG_MEMCG_SWAP
static struct cftype memsw_cgroup_files[] = {
        {
                .name = "memsw.usage_in_bytes",
                .private = MEMFILE_PRIVATE(_MEMSWAP, RES_USAGE),
                .read = mem_cgroup_read,
                .register_event = mem_cgroup_usage_register_event,
                .unregister_event = mem_cgroup_usage_unregister_event,
        },
        {
                .name = "memsw.max_usage_in_bytes",
                .private = MEMFILE_PRIVATE(_MEMSWAP, RES_MAX_USAGE),
                .trigger = mem_cgroup_reset,
                .read = mem_cgroup_read,
        },
        {
                .name = "memsw.limit_in_bytes",
                .private = MEMFILE_PRIVATE(_MEMSWAP, RES_LIMIT),
                .write_string = mem_cgroup_write,
                .read = mem_cgroup_read,
        },
        {
                .name = "memsw.failcnt",
                .private = MEMFILE_PRIVATE(_MEMSWAP, RES_FAILCNT),
                .trigger = mem_cgroup_reset,
                .read = mem_cgroup_read,
        },
        { },    /* terminate */
};
#endif
static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *memcg, int node)
{
        struct mem_cgroup_per_node *pn;
        struct mem_cgroup_per_zone *mz;
        int zone, tmp = node;
        /*
         * This routine is called against possible nodes.
         * But it's BUG to call kmalloc() against offline node.
         *
         * TODO: this routine can waste much memory for nodes which will
         *       never be onlined. It's better to use memory hotplug callback
         *       function.
         */
        if (!node_state(node, N_NORMAL_MEMORY))
                tmp = -1;
        pn = kzalloc_node(sizeof(*pn), GFP_KERNEL, tmp);
        if (!pn)
                return 1;

        for (zone = 0; zone < MAX_NR_ZONES; zone++) {
                mz = &pn->zoneinfo[zone];
                lruvec_init(&mz->lruvec);
                mz->memcg = memcg;
        }
        memcg->nodeinfo[node] = pn;
        return 0;
}

static void free_mem_cgroup_per_zone_info(struct mem_cgroup *memcg, int node)
{
        kfree(memcg->nodeinfo[node]);
}

static struct mem_cgroup *mem_cgroup_alloc(void)
{
        struct mem_cgroup *memcg;
        size_t size = memcg_size();

        /* Can be very big if nr_node_ids is very big */
        if (size < PAGE_SIZE)
                memcg = kzalloc(size, GFP_KERNEL);
        else
                memcg = vzalloc(size);

        if (!memcg)
                return NULL;

        memcg->stat = alloc_percpu(struct mem_cgroup_stat_cpu);
        if (!memcg->stat)
                goto out_free;
        spin_lock_init(&memcg->pcp_counter_lock);
        return memcg;

out_free:
        if (size < PAGE_SIZE)
                kfree(memcg);
        else
                vfree(memcg);
        return NULL;
}

/*
 * At destroying mem_cgroup, references from swap_cgroup can remain.
 * (scanning all at force_empty is too costly...)
 *
 * Instead of clearing all references at force_empty, we remember
 * the number of reference from swap_cgroup and free mem_cgroup when
 * it goes down to 0.
 *
 * Removal of cgroup itself succeeds regardless of refs from swap.
 */

static void __mem_cgroup_free(struct mem_cgroup *memcg)
{
        int node;
        size_t size = memcg_size();

        free_css_id(&mem_cgroup_subsys, &memcg->css);

        for_each_node(node)
                free_mem_cgroup_per_zone_info(memcg, node);

        free_percpu(memcg->stat);

        /*
         * We need to make sure that (at least for now), the jump label
         * destruction code runs outside of the cgroup lock. This is because
         * get_online_cpus(), which is called from the static_branch update,
         * can't be called inside the cgroup_lock. cpusets are the ones
         * enforcing this dependency, so if they ever change, we might as well.
         *
         * schedule_work() will guarantee this happens. Be careful if you need
         * to move this code around, and make sure it is outside
         * the cgroup_lock.
         */
        disarm_static_keys(memcg);
        if (size < PAGE_SIZE)
                kfree(memcg);
        else
                vfree(memcg);
}

/*
 * Returns the parent mem_cgroup in memcgroup hierarchy with hierarchy enabled.
 */
struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *memcg)
{
        if (!memcg->res.parent)
                return NULL;
        return mem_cgroup_from_res_counter(memcg->res.parent, res);
}
EXPORT_SYMBOL(parent_mem_cgroup);

static struct cgroup_subsys_state * __ref
mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
{
        struct mem_cgroup *memcg;
        long error = -ENOMEM;
        int node;

        memcg = mem_cgroup_alloc();
        if (!memcg)
                return ERR_PTR(error);

        for_each_node(node)
                if (alloc_mem_cgroup_per_zone_info(memcg, node))
                        goto free_out;

        /* root ? */
        if (parent_css == NULL) {
                root_mem_cgroup = memcg;
                res_counter_init(&memcg->res, NULL);
                res_counter_init(&memcg->memsw, NULL);
                res_counter_init(&memcg->kmem, NULL);
        }

        memcg->last_scanned_node = MAX_NUMNODES;
        INIT_LIST_HEAD(&memcg->oom_notify);
        memcg->move_charge_at_immigrate = 0;
        mutex_init(&memcg->thresholds_lock);
        spin_lock_init(&memcg->move_lock);
        vmpressure_init(&memcg->vmpressure);
        spin_lock_init(&memcg->soft_lock);

        return &memcg->css;

free_out:
        __mem_cgroup_free(memcg);
        return ERR_PTR(error);
}

static int
mem_cgroup_css_online(struct cgroup_subsys_state *css)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
        struct mem_cgroup *parent = mem_cgroup_from_css(css_parent(css));
        int error = 0;

        if (!parent)
                return 0;

        mutex_lock(&memcg_create_mutex);

        memcg->use_hierarchy = parent->use_hierarchy;
        memcg->oom_kill_disable = parent->oom_kill_disable;
        memcg->swappiness = mem_cgroup_swappiness(parent);

        if (parent->use_hierarchy) {
                res_counter_init(&memcg->res, &parent->res);
                res_counter_init(&memcg->memsw, &parent->memsw);
                res_counter_init(&memcg->kmem, &parent->kmem);

                /*
                 * No need to take a reference to the parent because cgroup
                 * core guarantees its existence.
                 */
        } else {
                res_counter_init(&memcg->res, NULL);
                res_counter_init(&memcg->memsw, NULL);
                res_counter_init(&memcg->kmem, NULL);
                /*
                 * Deeper hierachy with use_hierarchy == false doesn't make
                 * much sense so let cgroup subsystem know about this
                 * unfortunate state in our controller.
                 */
                if (parent != root_mem_cgroup)
                        mem_cgroup_subsys.broken_hierarchy = true;
        }

        error = memcg_init_kmem(memcg, &mem_cgroup_subsys);
        mutex_unlock(&memcg_create_mutex);
        return error;
}

/*
 * Announce all parents that a group from their hierarchy is gone.
 */
static void mem_cgroup_invalidate_reclaim_iterators(struct mem_cgroup *memcg)
{
        struct mem_cgroup *parent = memcg;

        while ((parent = parent_mem_cgroup(parent)))
                mem_cgroup_iter_invalidate(parent);

        /*
         * if the root memcg is not hierarchical we have to check it
         * explicitely.
         */
        if (!root_mem_cgroup->use_hierarchy)
                mem_cgroup_iter_invalidate(root_mem_cgroup);
}

static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);

        kmem_cgroup_css_offline(memcg);

        mem_cgroup_invalidate_reclaim_iterators(memcg);
        mem_cgroup_reparent_charges(memcg);
        if (memcg->soft_contributed) {
                while ((memcg = parent_mem_cgroup(memcg)))
                        atomic_dec(&memcg->children_in_excess);
        }
        mem_cgroup_destroy_all_caches(memcg);
        vmpressure_cleanup(&memcg->vmpressure);
}

static void mem_cgroup_css_free(struct cgroup_subsys_state *css)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);

        memcg_destroy_kmem(memcg);
        __mem_cgroup_free(memcg);
}

#ifdef CONFIG_MMU
/* Handlers for move charge at task migration. */
#define PRECHARGE_COUNT_AT_ONCE 256
static int mem_cgroup_do_precharge(unsigned long count)
{
        int ret = 0;
        int batch_count = PRECHARGE_COUNT_AT_ONCE;
        struct mem_cgroup *memcg = mc.to;

        if (mem_cgroup_is_root(memcg)) {
                mc.precharge += count;
                /* we don't need css_get for root */
                return ret;
        }
        /* try to charge at once */
        if (count > 1) {
                struct res_counter *dummy;
                /*
                 * "memcg" cannot be under rmdir() because we've already checked
                 * by cgroup_lock_live_cgroup() that it is not removed and we
                 * are still under the same cgroup_mutex. So we can postpone
                 * css_get().
                 */
                if (res_counter_charge(&memcg->res, PAGE_SIZE * count, &dummy))
                        goto one_by_one;
                if (do_swap_account && res_counter_charge(&memcg->memsw,
                                                PAGE_SIZE * count, &dummy)) {
                        res_counter_uncharge(&memcg->res, PAGE_SIZE * count);
                        goto one_by_one;
                }
                mc.precharge += count;
                return ret;
        }
one_by_one:
        /* fall back to one by one charge */
        while (count--) {
                if (signal_pending(current)) {
                        ret = -EINTR;
                        break;
                }
                if (!batch_count--) {
                        batch_count = PRECHARGE_COUNT_AT_ONCE;
                        cond_resched();
                }
                ret = __mem_cgroup_try_charge(NULL,
                                        GFP_KERNEL, 1, &memcg, false);
                if (ret)
                        /* mem_cgroup_clear_mc() will do uncharge later */
                        return ret;
                mc.precharge++;
        }
        return ret;
}

/**
 * get_mctgt_type - get target type of moving charge
 * @vma: the vma the pte to be checked belongs
 * @addr: the address corresponding to the pte to be checked
 * @ptent: the pte to be checked
 * @target: the pointer the target page or swap ent will be stored(can be NULL)
 *
 * Returns
 *   0(MC_TARGET_NONE): if the pte is not a target for move charge.
 *   1(MC_TARGET_PAGE): if the page corresponding to this pte is a target for
 *     move charge. if @target is not NULL, the page is stored in target->page
 *     with extra refcnt got(Callers should handle it).
 *   2(MC_TARGET_SWAP): if the swap entry corresponding to this pte is a
 *     target for charge migration. if @target is not NULL, the entry is stored
 *     in target->ent.
 *
 * Called with pte lock held.
 */
union mc_target {
        struct page     *page;
        swp_entry_t     ent;
};

enum mc_target_type {
        MC_TARGET_NONE = 0,
        MC_TARGET_PAGE,
        MC_TARGET_SWAP,
};

static struct page *mc_handle_present_pte(struct vm_area_struct *vma,
                                                unsigned long addr, pte_t ptent)
{
        struct page *page = vm_normal_page(vma, addr, ptent);

        if (!page || !page_mapped(page))
                return NULL;
        if (PageAnon(page)) {
                /* we don't move shared anon */
                if (!move_anon())
                        return NULL;
        } else if (!move_file())
                /* we ignore mapcount for file pages */
                return NULL;
        if (!get_page_unless_zero(page))
                return NULL;

        return page;
}

#ifdef CONFIG_SWAP
static struct page *mc_handle_swap_pte(struct vm_area_struct *vma,
                        unsigned long addr, pte_t ptent, swp_entry_t *entry)
{
        struct page *page = NULL;
        swp_entry_t ent = pte_to_swp_entry(ptent);

        if (!move_anon() || non_swap_entry(ent))
                return NULL;
        /*
         * Because lookup_swap_cache() updates some statistics counter,
         * we call find_get_page() with swapper_space directly.
         */
        page = find_get_page(swap_address_space(ent), ent.val);
        if (do_swap_account)
                entry->val = ent.val;

        return page;
}
#else
static struct page *mc_handle_swap_pte(struct vm_area_struct *vma,
                        unsigned long addr, pte_t ptent, swp_entry_t *entry)
{
        return NULL;
}
#endif

static struct page *mc_handle_file_pte(struct vm_area_struct *vma,
                        unsigned long addr, pte_t ptent, swp_entry_t *entry)
{
        struct page *page = NULL;
        struct address_space *mapping;
        pgoff_t pgoff;

        if (!vma->vm_file) /* anonymous vma */
                return NULL;
        if (!move_file())
                return NULL;

        mapping = vma->vm_file->f_mapping;
        if (pte_none(ptent))
                pgoff = linear_page_index(vma, addr);
        else /* pte_file(ptent) is true */
                pgoff = pte_to_pgoff(ptent);

        /* page is moved even if it's not RSS of this task(page-faulted). */
        page = find_get_page(mapping, pgoff);

#ifdef CONFIG_SWAP
        /* shmem/tmpfs may report page out on swap: account for that too. */
        if (radix_tree_exceptional_entry(page)) {
                swp_entry_t swap = radix_to_swp_entry(page);
                if (do_swap_account)
                        *entry = swap;
                page = find_get_page(swap_address_space(swap), swap.val);
        }
#endif
        return page;
}

static enum mc_target_type get_mctgt_type(struct vm_area_struct *vma,
                unsigned long addr, pte_t ptent, union mc_target *target)
{
        struct page *page = NULL;
        struct page_cgroup *pc;
        enum mc_target_type ret = MC_TARGET_NONE;
        swp_entry_t ent = { .val = 0 };

        if (pte_present(ptent))
                page = mc_handle_present_pte(vma, addr, ptent);
        else if (is_swap_pte(ptent))
                page = mc_handle_swap_pte(vma, addr, ptent, &ent);
        else if (pte_none(ptent) || pte_file(ptent))
                page = mc_handle_file_pte(vma, addr, ptent, &ent);

        if (!page && !ent.val)
                return ret;
        if (page) {
                pc = lookup_page_cgroup(page);
                /*
                 * Do only loose check w/o page_cgroup lock.
                 * mem_cgroup_move_account() checks the pc is valid or not under
                 * the lock.
                 */
                if (PageCgroupUsed(pc) && pc->mem_cgroup == mc.from) {
                        ret = MC_TARGET_PAGE;
                        if (target)
                                target->page = page;
                }
                if (!ret || !target)
                        put_page(page);
        }
        /* There is a swap entry and a page doesn't exist or isn't charged */
        if (ent.val && !ret &&
                        css_id(&mc.from->css) == lookup_swap_cgroup_id(ent)) {
                ret = MC_TARGET_SWAP;
                if (target)
                        target->ent = ent;
        }
        return ret;
}

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
/*
 * We don't consider swapping or file mapped pages because THP does not
 * support them for now.
 * Caller should make sure that pmd_trans_huge(pmd) is true.
 */
static enum mc_target_type get_mctgt_type_thp(struct vm_area_struct *vma,
                unsigned long addr, pmd_t pmd, union mc_target *target)
{
        struct page *page = NULL;
        struct page_cgroup *pc;
        enum mc_target_type ret = MC_TARGET_NONE;

        page = pmd_page(pmd);
        VM_BUG_ON(!page || !PageHead(page));
        if (!move_anon())
                return ret;
        pc = lookup_page_cgroup(page);
        if (PageCgroupUsed(pc) && pc->mem_cgroup == mc.from) {
                ret = MC_TARGET_PAGE;
                if (target) {
                        get_page(page);
                        target->page = page;
                }
        }
        return ret;
}
#else
static inline enum mc_target_type get_mctgt_type_thp(struct vm_area_struct *vma,
                unsigned long addr, pmd_t pmd, union mc_target *target)
{
        return MC_TARGET_NONE;
}
#endif

static int mem_cgroup_count_precharge_pte_range(pmd_t *pmd,
                                        unsigned long addr, unsigned long end,
                                        struct mm_walk *walk)
{
        struct vm_area_struct *vma = walk->private;
        pte_t *pte;
        spinlock_t *ptl;

        if (pmd_trans_huge_lock(pmd, vma) == 1) {
                if (get_mctgt_type_thp(vma, addr, *pmd, NULL) == MC_TARGET_PAGE)
                        mc.precharge += HPAGE_PMD_NR;
                spin_unlock(&vma->vm_mm->page_table_lock);
                return 0;
        }

        if (pmd_trans_unstable(pmd))
                return 0;
        pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
        for (; addr != end; pte++, addr += PAGE_SIZE)
                if (get_mctgt_type(vma, addr, *pte, NULL))
                        mc.precharge++; /* increment precharge temporarily */
        pte_unmap_unlock(pte - 1, ptl);
        cond_resched();

        return 0;
}

static unsigned long mem_cgroup_count_precharge(struct mm_struct *mm)
{
        unsigned long precharge;
        struct vm_area_struct *vma;

        down_read(&mm->mmap_sem);
        for (vma = mm->mmap; vma; vma = vma->vm_next) {
                struct mm_walk mem_cgroup_count_precharge_walk = {
                        .pmd_entry = mem_cgroup_count_precharge_pte_range,
                        .mm = mm,
                        .private = vma,
                };
                if (is_vm_hugetlb_page(vma))
                        continue;
                walk_page_range(vma->vm_start, vma->vm_end,
                                        &mem_cgroup_count_precharge_walk);
        }
        up_read(&mm->mmap_sem);

        precharge = mc.precharge;
        mc.precharge = 0;

        return precharge;
}

static int mem_cgroup_precharge_mc(struct mm_struct *mm)
{
        unsigned long precharge = mem_cgroup_count_precharge(mm);

        VM_BUG_ON(mc.moving_task);
        mc.moving_task = current;
        return mem_cgroup_do_precharge(precharge);
}

/* cancels all extra charges on mc.from and mc.to, and wakes up all waiters. */
static void __mem_cgroup_clear_mc(void)
{
        struct mem_cgroup *from = mc.from;
        struct mem_cgroup *to = mc.to;
        int i;

        /* we must uncharge all the leftover precharges from mc.to */
        if (mc.precharge) {
                __mem_cgroup_cancel_charge(mc.to, mc.precharge);
                mc.precharge = 0;
        }
        /*
         * we didn't uncharge from mc.from at mem_cgroup_move_account(), so
         * we must uncharge here.
         */
        if (mc.moved_charge) {
                __mem_cgroup_cancel_charge(mc.from, mc.moved_charge);
                mc.moved_charge = 0;
        }
        /* we must fixup refcnts and charges */
        if (mc.moved_swap) {
                /* uncharge swap account from the old cgroup */
                if (!mem_cgroup_is_root(mc.from))
                        res_counter_uncharge(&mc.from->memsw,
                                                PAGE_SIZE * mc.moved_swap);

                for (i = 0; i < mc.moved_swap; i++)
                        css_put(&mc.from->css);

                if (!mem_cgroup_is_root(mc.to)) {
                        /*
                         * we charged both to->res and to->memsw, so we should
                         * uncharge to->res.
                         */
                        res_counter_uncharge(&mc.to->res,
                                                PAGE_SIZE * mc.moved_swap);
                }
                /* we've already done css_get(mc.to) */
                mc.moved_swap = 0;
        }
        memcg_oom_recover(from);
        memcg_oom_recover(to);
        wake_up_all(&mc.waitq);
}

static void mem_cgroup_clear_mc(void)
{
        struct mem_cgroup *from = mc.from;

        /*
         * we must clear moving_task before waking up waiters at the end of
         * task migration.
         */
        mc.moving_task = NULL;
        __mem_cgroup_clear_mc();
        spin_lock(&mc.lock);
        mc.from = NULL;
        mc.to = NULL;
        spin_unlock(&mc.lock);
        mem_cgroup_end_move(from);
}

static int mem_cgroup_can_attach(struct cgroup_subsys_state *css,
                                 struct cgroup_taskset *tset)
{
        struct task_struct *p = cgroup_taskset_first(tset);
        int ret = 0;
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
        unsigned long move_charge_at_immigrate;

        /*
         * We are now commited to this value whatever it is. Changes in this
         * tunable will only affect upcoming migrations, not the current one.
         * So we need to save it, and keep it going.
         */
        move_charge_at_immigrate  = memcg->move_charge_at_immigrate;
        if (move_charge_at_immigrate) {
                struct mm_struct *mm;
                struct mem_cgroup *from = mem_cgroup_from_task(p);

                VM_BUG_ON(from == memcg);

                mm = get_task_mm(p);
                if (!mm)
                        return 0;
                /* We move charges only when we move a owner of the mm */
                if (mm->owner == p) {
                        VM_BUG_ON(mc.from);
                        VM_BUG_ON(mc.to);
                        VM_BUG_ON(mc.precharge);
                        VM_BUG_ON(mc.moved_charge);
                        VM_BUG_ON(mc.moved_swap);
                        mem_cgroup_start_move(from);
                        spin_lock(&mc.lock);
                        mc.from = from;
                        mc.to = memcg;
                        mc.immigrate_flags = move_charge_at_immigrate;
                        spin_unlock(&mc.lock);
                        /* We set mc.moving_task later */

                        ret = mem_cgroup_precharge_mc(mm);
                        if (ret)
                                mem_cgroup_clear_mc();
                }
                mmput(mm);
        }
        return ret;
}

static void mem_cgroup_cancel_attach(struct cgroup_subsys_state *css,
                                     struct cgroup_taskset *tset)
{
        mem_cgroup_clear_mc();
}

static int mem_cgroup_move_charge_pte_range(pmd_t *pmd,
                                unsigned long addr, unsigned long end,
                                struct mm_walk *walk)
{
        int ret = 0;
        struct vm_area_struct *vma = walk->private;
        pte_t *pte;
        spinlock_t *ptl;
        enum mc_target_type target_type;
        union mc_target target;
        struct page *page;
        struct page_cgroup *pc;

        /*
         * We don't take compound_lock() here but no race with splitting thp
         * happens because:
         *  - if pmd_trans_huge_lock() returns 1, the relevant thp is not
         *    under splitting, which means there's no concurrent thp split,
         *  - if another thread runs into split_huge_page() just after we
         *    entered this if-block, the thread must wait for page table lock
         *    to be unlocked in __split_huge_page_splitting(), where the main
         *    part of thp split is not executed yet.
         */
        if (pmd_trans_huge_lock(pmd, vma) == 1) {
                if (mc.precharge < HPAGE_PMD_NR) {
                        spin_unlock(&vma->vm_mm->page_table_lock);
                        return 0;
                }
                target_type = get_mctgt_type_thp(vma, addr, *pmd, &target);
                if (target_type == MC_TARGET_PAGE) {
                        page = target.page;
                        if (!isolate_lru_page(page)) {
                                pc = lookup_page_cgroup(page);
                                if (!mem_cgroup_move_account(page, HPAGE_PMD_NR,
                                                        pc, mc.from, mc.to)) {
                                        mc.precharge -= HPAGE_PMD_NR;
                                        mc.moved_charge += HPAGE_PMD_NR;
                                }
                                putback_lru_page(page);
                        }
                        put_page(page);
                }
                spin_unlock(&vma->vm_mm->page_table_lock);
                return 0;
        }

        if (pmd_trans_unstable(pmd))
                return 0;
retry:
        pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
        for (; addr != end; addr += PAGE_SIZE) {
                pte_t ptent = *(pte++);
                swp_entry_t ent;

                if (!mc.precharge)
                        break;

                switch (get_mctgt_type(vma, addr, ptent, &target)) {
                case MC_TARGET_PAGE:
                        page = target.page;
                        if (isolate_lru_page(page))
                                goto put;
                        pc = lookup_page_cgroup(page);
                        if (!mem_cgroup_move_account(page, 1, pc,
                                                     mc.from, mc.to)) {
                                mc.precharge--;
                                /* we uncharge from mc.from later. */
                                mc.moved_charge++;
                        }
                        putback_lru_page(page);
put:                    /* get_mctgt_type() gets the page */
                        put_page(page);
                        break;
                case MC_TARGET_SWAP:
                        ent = target.ent;
                        if (!mem_cgroup_move_swap_account(ent, mc.from, mc.to)) {
                                mc.precharge--;
                                /* we fixup refcnts and charges later. */
                                mc.moved_swap++;
                        }
                        break;
                default:
                        break;
                }
        }
        pte_unmap_unlock(pte - 1, ptl);
        cond_resched();

        if (addr != end) {
                /*
                 * We have consumed all precharges we got in can_attach().
                 * We try charge one by one, but don't do any additional
                 * charges to mc.to if we have failed in charge once in attach()
                 * phase.
                 */
                ret = mem_cgroup_do_precharge(1);
                if (!ret)
                        goto retry;
        }

        return ret;
}

static void mem_cgroup_move_charge(struct mm_struct *mm)
{
        struct vm_area_struct *vma;

        lru_add_drain_all();
retry:
        if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
                /*
                 * Someone who are holding the mmap_sem might be waiting in
                 * waitq. So we cancel all extra charges, wake up all waiters,
                 * and retry. Because we cancel precharges, we might not be able
                 * to move enough charges, but moving charge is a best-effort
                 * feature anyway, so it wouldn't be a big problem.
                 */
                __mem_cgroup_clear_mc();
                cond_resched();
                goto retry;
        }
        for (vma = mm->mmap; vma; vma = vma->vm_next) {
                int ret;
                struct mm_walk mem_cgroup_move_charge_walk = {
                        .pmd_entry = mem_cgroup_move_charge_pte_range,
                        .mm = mm,
                        .private = vma,
                };
                if (is_vm_hugetlb_page(vma))
                        continue;
                ret = walk_page_range(vma->vm_start, vma->vm_end,
                                                &mem_cgroup_move_charge_walk);
                if (ret)
                        /*
                         * means we have consumed all precharges and failed in
                         * doing additional charge. Just abandon here.
                         */
                        break;
        }
        up_read(&mm->mmap_sem);
}

static void mem_cgroup_move_task(struct cgroup_subsys_state *css,
                                 struct cgroup_taskset *tset)
{
        struct task_struct *p = cgroup_taskset_first(tset);
        struct mm_struct *mm = get_task_mm(p);

        if (mm) {
                if (mc.to)
                        mem_cgroup_move_charge(mm);
                mmput(mm);
        }
        if (mc.to)
                mem_cgroup_clear_mc();
}
#else   /* !CONFIG_MMU */
static int mem_cgroup_can_attach(struct cgroup_subsys_state *css,
                                 struct cgroup_taskset *tset)
{
        return 0;
}
static void mem_cgroup_cancel_attach(struct cgroup_subsys_state *css,
                                     struct cgroup_taskset *tset)
{
}
static void mem_cgroup_move_task(struct cgroup_subsys_state *css,
                                 struct cgroup_taskset *tset)
{
}
#endif

/*
 * Cgroup retains root cgroups across [un]mount cycles making it necessary
 * to verify sane_behavior flag on each mount attempt.
 */
static void mem_cgroup_bind(struct cgroup_subsys_state *root_css)
{
        /*
         * use_hierarchy is forced with sane_behavior.  cgroup core
         * guarantees that @root doesn't have any children, so turning it
         * on for the root memcg is enough.
         */
        if (cgroup_sane_behavior(root_css->cgroup))
                mem_cgroup_from_css(root_css)->use_hierarchy = true;
}

struct cgroup_subsys mem_cgroup_subsys = {
        .name = "memory",
        .subsys_id = mem_cgroup_subsys_id,
        .css_alloc = mem_cgroup_css_alloc,
        .css_online = mem_cgroup_css_online,
        .css_offline = mem_cgroup_css_offline,
        .css_free = mem_cgroup_css_free,
        .can_attach = mem_cgroup_can_attach,
        .cancel_attach = mem_cgroup_cancel_attach,
        .attach = mem_cgroup_move_task,
        .bind = mem_cgroup_bind,
        .base_cftypes = mem_cgroup_files,
        .early_init = 0,
        .use_id = 1,
};

#ifdef CONFIG_MEMCG_SWAP
static int __init enable_swap_account(char *s)
{
        if (!strcmp(s, "1"))
                really_do_swap_account = 1;
        else if (!strcmp(s, "0"))
                really_do_swap_account = 0;
        return 1;
}
__setup("swapaccount=", enable_swap_account);

static void __init memsw_file_init(void)
{
        WARN_ON(cgroup_add_cftypes(&mem_cgroup_subsys, memsw_cgroup_files));
}

static void __init enable_swap_cgroup(void)
{
        if (!mem_cgroup_disabled() && really_do_swap_account) {
                do_swap_account = 1;
                memsw_file_init();
        }
}

#else
static void __init enable_swap_cgroup(void)
{
}
#endif

/*
 * subsys_initcall() for memory controller.
 *
 * Some parts like hotcpu_notifier() have to be initialized from this context
 * because of lock dependencies (cgroup_lock -> cpu hotplug) but basically
 * everything that doesn't depend on a specific mem_cgroup structure should
 * be initialized from here.
 */
static int __init mem_cgroup_init(void)
{
        hotcpu_notifier(memcg_cpu_hotplug_callback, 0);
        enable_swap_cgroup();
        memcg_stock_init();
        return 0;
}
subsys_initcall(mem_cgroup_init);