[platform/kernel/linux-rpi.git] / mm / memory_hotplug.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/mm/memory_hotplug.c
 *
 *  Copyright (C)
 */

#include <linux/stddef.h>
#include <linux/mm.h>
#include <linux/sched/signal.h>
#include <linux/swap.h>
#include <linux/interrupt.h>
#include <linux/pagemap.h>
#include <linux/compiler.h>
#include <linux/export.h>
#include <linux/pagevec.h>
#include <linux/writeback.h>
#include <linux/slab.h>
#include <linux/sysctl.h>
#include <linux/cpu.h>
#include <linux/memory.h>
#include <linux/memremap.h>
#include <linux/memory_hotplug.h>
#include <linux/highmem.h>
#include <linux/vmalloc.h>
#include <linux/ioport.h>
#include <linux/delay.h>
#include <linux/migrate.h>
#include <linux/page-isolation.h>
#include <linux/pfn.h>
#include <linux/suspend.h>
#include <linux/mm_inline.h>
#include <linux/firmware-map.h>
#include <linux/stop_machine.h>
#include <linux/hugetlb.h>
#include <linux/memblock.h>
#include <linux/compaction.h>
#include <linux/rmap.h>

#include <asm/tlbflush.h>

#include "internal.h"
#include "shuffle.h"

/*
 * online_page_callback contains pointer to current page onlining function.
 * Initially it is generic_online_page(). If it is required it could be
 * changed by calling set_online_page_callback() for callback registration
 * and restore_online_page_callback() for generic callback restore.
 */

static void generic_online_page(struct page *page, unsigned int order);

static online_page_callback_t online_page_callback = generic_online_page;
static DEFINE_MUTEX(online_page_callback_lock);

DEFINE_STATIC_PERCPU_RWSEM(mem_hotplug_lock);

void get_online_mems(void)
{
        percpu_down_read(&mem_hotplug_lock);
}

void put_online_mems(void)
{
        percpu_up_read(&mem_hotplug_lock);
}

bool movable_node_enabled = false;

#ifndef CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE
bool memhp_auto_online;
#else
bool memhp_auto_online = true;
#endif
EXPORT_SYMBOL_GPL(memhp_auto_online);

static int __init setup_memhp_default_state(char *str)
{
        if (!strcmp(str, "online"))
                memhp_auto_online = true;
        else if (!strcmp(str, "offline"))
                memhp_auto_online = false;

        return 1;
}
__setup("memhp_default_state=", setup_memhp_default_state);

void mem_hotplug_begin(void)
{
        cpus_read_lock();
        percpu_down_write(&mem_hotplug_lock);
}

void mem_hotplug_done(void)
{
        percpu_up_write(&mem_hotplug_lock);
        cpus_read_unlock();
}

u64 max_mem_size = U64_MAX;

/* add this memory to iomem resource */
static struct resource *register_memory_resource(u64 start, u64 size)
{
        struct resource *res;
        unsigned long flags =  IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
        char *resource_name = "System RAM";

        if (start + size > max_mem_size)
                return ERR_PTR(-E2BIG);

        /*
         * Request ownership of the new memory range.  This might be
         * a child of an existing resource that was present but
         * not marked as busy.
         */
        res = __request_region(&iomem_resource, start, size,
                               resource_name, flags);

        if (!res) {
                pr_debug("Unable to reserve System RAM region: %016llx->%016llx\n",
                                start, start + size);
                return ERR_PTR(-EEXIST);
        }
        return res;
}

static void release_memory_resource(struct resource *res)
{
        if (!res)
                return;
        release_resource(res);
        kfree(res);
}

#ifdef CONFIG_MEMORY_HOTPLUG_SPARSE
void get_page_bootmem(unsigned long info,  struct page *page,
                      unsigned long type)
{
        page->freelist = (void *)type;
        SetPagePrivate(page);
        set_page_private(page, info);
        page_ref_inc(page);
}

void put_page_bootmem(struct page *page)
{
        unsigned long type;

        type = (unsigned long) page->freelist;
        BUG_ON(type < MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE ||
               type > MEMORY_HOTPLUG_MAX_BOOTMEM_TYPE);

        if (page_ref_dec_return(page) == 1) {
                page->freelist = NULL;
                ClearPagePrivate(page);
                set_page_private(page, 0);
                INIT_LIST_HEAD(&page->lru);
                free_reserved_page(page);
        }
}

#ifdef CONFIG_HAVE_BOOTMEM_INFO_NODE
#ifndef CONFIG_SPARSEMEM_VMEMMAP
static void register_page_bootmem_info_section(unsigned long start_pfn)
{
        unsigned long mapsize, section_nr, i;
        struct mem_section *ms;
        struct page *page, *memmap;
        struct mem_section_usage *usage;

        section_nr = pfn_to_section_nr(start_pfn);
        ms = __nr_to_section(section_nr);

        /* Get section's memmap address */
        memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr);

        /*
         * Get page for the memmap's phys address
         * XXX: need more consideration for sparse_vmemmap...
         */
        page = virt_to_page(memmap);
        mapsize = sizeof(struct page) * PAGES_PER_SECTION;
        mapsize = PAGE_ALIGN(mapsize) >> PAGE_SHIFT;

        /* remember memmap's page */
        for (i = 0; i < mapsize; i++, page++)
                get_page_bootmem(section_nr, page, SECTION_INFO);

        usage = ms->usage;
        page = virt_to_page(usage);

        mapsize = PAGE_ALIGN(mem_section_usage_size()) >> PAGE_SHIFT;

        for (i = 0; i < mapsize; i++, page++)
                get_page_bootmem(section_nr, page, MIX_SECTION_INFO);

}
#else /* CONFIG_SPARSEMEM_VMEMMAP */
static void register_page_bootmem_info_section(unsigned long start_pfn)
{
        unsigned long mapsize, section_nr, i;
        struct mem_section *ms;
        struct page *page, *memmap;
        struct mem_section_usage *usage;

        section_nr = pfn_to_section_nr(start_pfn);
        ms = __nr_to_section(section_nr);

        memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr);

        register_page_bootmem_memmap(section_nr, memmap, PAGES_PER_SECTION);

        usage = ms->usage;
        page = virt_to_page(usage);

        mapsize = PAGE_ALIGN(mem_section_usage_size()) >> PAGE_SHIFT;

        for (i = 0; i < mapsize; i++, page++)
                get_page_bootmem(section_nr, page, MIX_SECTION_INFO);
}
#endif /* !CONFIG_SPARSEMEM_VMEMMAP */

void __init register_page_bootmem_info_node(struct pglist_data *pgdat)
{
        unsigned long i, pfn, end_pfn, nr_pages;
        int node = pgdat->node_id;
        struct page *page;

        nr_pages = PAGE_ALIGN(sizeof(struct pglist_data)) >> PAGE_SHIFT;
        page = virt_to_page(pgdat);

        for (i = 0; i < nr_pages; i++, page++)
                get_page_bootmem(node, page, NODE_INFO);

        pfn = pgdat->node_start_pfn;
        end_pfn = pgdat_end_pfn(pgdat);

        /* register section info */
        for (; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
                /*
                 * Some platforms can assign the same pfn to multiple nodes - on
                 * node0 as well as nodeN.  To avoid registering a pfn against
                 * multiple nodes we check that this pfn does not already
                 * reside in some other nodes.
                 */
                if (pfn_valid(pfn) && (early_pfn_to_nid(pfn) == node))
                        register_page_bootmem_info_section(pfn);
        }
}
#endif /* CONFIG_HAVE_BOOTMEM_INFO_NODE */

static int check_pfn_span(unsigned long pfn, unsigned long nr_pages,
                const char *reason)
{
        /*
         * Disallow all operations smaller than a sub-section and only
         * allow operations smaller than a section for
         * SPARSEMEM_VMEMMAP. Note that check_hotplug_memory_range()
         * enforces a larger memory_block_size_bytes() granularity for
         * memory that will be marked online, so this check should only
         * fire for direct arch_{add,remove}_memory() users outside of
         * add_memory_resource().
         */
        unsigned long min_align;

        if (IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP))
                min_align = PAGES_PER_SUBSECTION;
        else
                min_align = PAGES_PER_SECTION;
        if (!IS_ALIGNED(pfn, min_align)
                        || !IS_ALIGNED(nr_pages, min_align)) {
                WARN(1, "Misaligned __%s_pages start: %#lx end: #%lx\n",
                                reason, pfn, pfn + nr_pages - 1);
                return -EINVAL;
        }
        return 0;
}

/*
 * Reasonably generic function for adding memory.  It is
 * expected that archs that support memory hotplug will
 * call this function after deciding the zone to which to
 * add the new pages.
 */
int __ref __add_pages(int nid, unsigned long pfn, unsigned long nr_pages,
                struct mhp_restrictions *restrictions)
{
        int err;
        unsigned long nr, start_sec, end_sec;
        struct vmem_altmap *altmap = restrictions->altmap;

        if (altmap) {
                /*
                 * Validate altmap is within bounds of the total request
                 */
                if (altmap->base_pfn != pfn
                                || vmem_altmap_offset(altmap) > nr_pages) {
                        pr_warn_once("memory add fail, invalid altmap\n");
                        return -EINVAL;
                }
                altmap->alloc = 0;
        }

        err = check_pfn_span(pfn, nr_pages, "add");
        if (err)
                return err;

        start_sec = pfn_to_section_nr(pfn);
        end_sec = pfn_to_section_nr(pfn + nr_pages - 1);
        for (nr = start_sec; nr <= end_sec; nr++) {
                unsigned long pfns;

                pfns = min(nr_pages, PAGES_PER_SECTION
                                - (pfn & ~PAGE_SECTION_MASK));
                err = sparse_add_section(nid, pfn, pfns, altmap);
                if (err)
                        break;
                pfn += pfns;
                nr_pages -= pfns;
                cond_resched();
        }
        vmemmap_populate_print_last();
        return err;
}

/* find the smallest valid pfn in the range [start_pfn, end_pfn) */
static unsigned long find_smallest_section_pfn(int nid, struct zone *zone,
                                     unsigned long start_pfn,
                                     unsigned long end_pfn)
{
        for (; start_pfn < end_pfn; start_pfn += PAGES_PER_SUBSECTION) {
                if (unlikely(!pfn_to_online_page(start_pfn)))
                        continue;

                if (unlikely(pfn_to_nid(start_pfn) != nid))
                        continue;

                if (zone && zone != page_zone(pfn_to_page(start_pfn)))
                        continue;

                return start_pfn;
        }

        return 0;
}

/* find the biggest valid pfn in the range [start_pfn, end_pfn). */
static unsigned long find_biggest_section_pfn(int nid, struct zone *zone,
                                    unsigned long start_pfn,
                                    unsigned long end_pfn)
{
        unsigned long pfn;

        /* pfn is the end pfn of a memory section. */
        pfn = end_pfn - 1;
        for (; pfn >= start_pfn; pfn -= PAGES_PER_SUBSECTION) {
                if (unlikely(!pfn_to_online_page(pfn)))
                        continue;

                if (unlikely(pfn_to_nid(pfn) != nid))
                        continue;

                if (zone && zone != page_zone(pfn_to_page(pfn)))
                        continue;

                return pfn;
        }

        return 0;
}

static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
                             unsigned long end_pfn)
{
        unsigned long zone_start_pfn = zone->zone_start_pfn;
        unsigned long z = zone_end_pfn(zone); /* zone_end_pfn namespace clash */
        unsigned long zone_end_pfn = z;
        unsigned long pfn;
        int nid = zone_to_nid(zone);

        zone_span_writelock(zone);
        if (zone_start_pfn == start_pfn) {
                /*
                 * If the section is smallest section in the zone, it need
                 * shrink zone->zone_start_pfn and zone->zone_spanned_pages.
                 * In this case, we find second smallest valid mem_section
                 * for shrinking zone.
                 */
                pfn = find_smallest_section_pfn(nid, zone, end_pfn,
                                                zone_end_pfn);
                if (pfn) {
                        zone->zone_start_pfn = pfn;
                        zone->spanned_pages = zone_end_pfn - pfn;
                }
        } else if (zone_end_pfn == end_pfn) {
                /*
                 * If the section is biggest section in the zone, it need
                 * shrink zone->spanned_pages.
                 * In this case, we find second biggest valid mem_section for
                 * shrinking zone.
                 */
                pfn = find_biggest_section_pfn(nid, zone, zone_start_pfn,
                                               start_pfn);
                if (pfn)
                        zone->spanned_pages = pfn - zone_start_pfn + 1;
        }

        /*
         * The section is not biggest or smallest mem_section in the zone, it
         * only creates a hole in the zone. So in this case, we need not
         * change the zone. But perhaps, the zone has only hole data. Thus
         * it check the zone has only hole or not.
         */
        pfn = zone_start_pfn;
        for (; pfn < zone_end_pfn; pfn += PAGES_PER_SUBSECTION) {
                if (unlikely(!pfn_to_online_page(pfn)))
                        continue;

                if (page_zone(pfn_to_page(pfn)) != zone)
                        continue;

                /* Skip range to be removed */
                if (pfn >= start_pfn && pfn < end_pfn)
                        continue;

                /* If we find valid section, we have nothing to do */
                zone_span_writeunlock(zone);
                return;
        }

        /* The zone has no valid section */
        zone->zone_start_pfn = 0;
        zone->spanned_pages = 0;
        zone_span_writeunlock(zone);
}

static void update_pgdat_span(struct pglist_data *pgdat)
{
        unsigned long node_start_pfn = 0, node_end_pfn = 0;
        struct zone *zone;

        for (zone = pgdat->node_zones;
             zone < pgdat->node_zones + MAX_NR_ZONES; zone++) {
                unsigned long zone_end_pfn = zone->zone_start_pfn +
                                             zone->spanned_pages;

                /* No need to lock the zones, they can't change. */
                if (!zone->spanned_pages)
                        continue;
                if (!node_end_pfn) {
                        node_start_pfn = zone->zone_start_pfn;
                        node_end_pfn = zone_end_pfn;
                        continue;
                }

                if (zone_end_pfn > node_end_pfn)
                        node_end_pfn = zone_end_pfn;
                if (zone->zone_start_pfn < node_start_pfn)
                        node_start_pfn = zone->zone_start_pfn;
        }

        pgdat->node_start_pfn = node_start_pfn;
        pgdat->node_spanned_pages = node_end_pfn - node_start_pfn;
}

void __ref remove_pfn_range_from_zone(struct zone *zone,
                                      unsigned long start_pfn,
                                      unsigned long nr_pages)
{
        struct pglist_data *pgdat = zone->zone_pgdat;
        unsigned long flags;

#ifdef CONFIG_ZONE_DEVICE
        /*
         * Zone shrinking code cannot properly deal with ZONE_DEVICE. So
         * we will not try to shrink the zones - which is okay as
         * set_zone_contiguous() cannot deal with ZONE_DEVICE either way.
         */
        if (zone_idx(zone) == ZONE_DEVICE)
                return;
#endif

        clear_zone_contiguous(zone);

        pgdat_resize_lock(zone->zone_pgdat, &flags);
        shrink_zone_span(zone, start_pfn, start_pfn + nr_pages);
        update_pgdat_span(pgdat);
        pgdat_resize_unlock(zone->zone_pgdat, &flags);

        set_zone_contiguous(zone);
}

static void __remove_section(unsigned long pfn, unsigned long nr_pages,
                             unsigned long map_offset,
                             struct vmem_altmap *altmap)
{
        struct mem_section *ms = __nr_to_section(pfn_to_section_nr(pfn));

        if (WARN_ON_ONCE(!valid_section(ms)))
                return;

        sparse_remove_section(ms, pfn, nr_pages, map_offset, altmap);
}

/**
 * __remove_pages() - remove sections of pages
 * @pfn: starting pageframe (must be aligned to start of a section)
 * @nr_pages: number of pages to remove (must be multiple of section size)
 * @altmap: alternative device page map or %NULL if default memmap is used
 *
 * Generic helper function to remove section mappings and sysfs entries
 * for the section of the memory we are removing. Caller needs to make
 * sure that pages are marked reserved and zones are adjust properly by
 * calling offline_pages().
 */
void __remove_pages(unsigned long pfn, unsigned long nr_pages,
                    struct vmem_altmap *altmap)
{
        unsigned long map_offset = 0;
        unsigned long nr, start_sec, end_sec;

        map_offset = vmem_altmap_offset(altmap);

        if (check_pfn_span(pfn, nr_pages, "remove"))
                return;

        start_sec = pfn_to_section_nr(pfn);
        end_sec = pfn_to_section_nr(pfn + nr_pages - 1);
        for (nr = start_sec; nr <= end_sec; nr++) {
                unsigned long pfns;

                cond_resched();
                pfns = min(nr_pages, PAGES_PER_SECTION
                                - (pfn & ~PAGE_SECTION_MASK));
                __remove_section(pfn, pfns, map_offset, altmap);
                pfn += pfns;
                nr_pages -= pfns;
                map_offset = 0;
        }
}

int set_online_page_callback(online_page_callback_t callback)
{
        int rc = -EINVAL;

        get_online_mems();
        mutex_lock(&online_page_callback_lock);

        if (online_page_callback == generic_online_page) {
                online_page_callback = callback;
                rc = 0;
        }

        mutex_unlock(&online_page_callback_lock);
        put_online_mems();

        return rc;
}
EXPORT_SYMBOL_GPL(set_online_page_callback);

int restore_online_page_callback(online_page_callback_t callback)
{
        int rc = -EINVAL;

        get_online_mems();
        mutex_lock(&online_page_callback_lock);

        if (online_page_callback == callback) {
                online_page_callback = generic_online_page;
                rc = 0;
        }

        mutex_unlock(&online_page_callback_lock);
        put_online_mems();

        return rc;
}
EXPORT_SYMBOL_GPL(restore_online_page_callback);

void __online_page_set_limits(struct page *page)
{
}
EXPORT_SYMBOL_GPL(__online_page_set_limits);

void __online_page_increment_counters(struct page *page)
{
        adjust_managed_page_count(page, 1);
}
EXPORT_SYMBOL_GPL(__online_page_increment_counters);

void __online_page_free(struct page *page)
{
        __free_reserved_page(page);
}
EXPORT_SYMBOL_GPL(__online_page_free);

static void generic_online_page(struct page *page, unsigned int order)
{
        /*
         * Freeing the page with debug_pagealloc enabled will try to unmap it,
         * so we should map it first. This is better than introducing a special
         * case in page freeing fast path.
         */
        if (debug_pagealloc_enabled_static())
                kernel_map_pages(page, 1 << order, 1);
        __free_pages_core(page, order);
        totalram_pages_add(1UL << order);
#ifdef CONFIG_HIGHMEM
        if (PageHighMem(page))
                totalhigh_pages_add(1UL << order);
#endif
}

static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
                        void *arg)
{
        const unsigned long end_pfn = start_pfn + nr_pages;
        unsigned long pfn;
        int order;

        /*
         * Online the pages. The callback might decide to keep some pages
         * PG_reserved (to add them to the buddy later), but we still account
         * them as being online/belonging to this zone ("present").
         */
        for (pfn = start_pfn; pfn < end_pfn; pfn += 1ul << order) {
                order = min(MAX_ORDER - 1, get_order(PFN_PHYS(end_pfn - pfn)));
                /* __free_pages_core() wants pfns to be aligned to the order */
                if (WARN_ON_ONCE(!IS_ALIGNED(pfn, 1ul << order)))
                        order = 0;
                (*online_page_callback)(pfn_to_page(pfn), order);
        }

        /* mark all involved sections as online */
        online_mem_sections(start_pfn, end_pfn);

        *(unsigned long *)arg += nr_pages;
        return 0;
}

/* check which state of node_states will be changed when online memory */
static void node_states_check_changes_online(unsigned long nr_pages,
        struct zone *zone, struct memory_notify *arg)
{
        int nid = zone_to_nid(zone);

        arg->status_change_nid = NUMA_NO_NODE;
        arg->status_change_nid_normal = NUMA_NO_NODE;
        arg->status_change_nid_high = NUMA_NO_NODE;

        if (!node_state(nid, N_MEMORY))
                arg->status_change_nid = nid;
        if (zone_idx(zone) <= ZONE_NORMAL && !node_state(nid, N_NORMAL_MEMORY))
                arg->status_change_nid_normal = nid;
#ifdef CONFIG_HIGHMEM
        if (zone_idx(zone) <= ZONE_HIGHMEM && !node_state(nid, N_HIGH_MEMORY))
                arg->status_change_nid_high = nid;
#endif
}

static void node_states_set_node(int node, struct memory_notify *arg)
{
        if (arg->status_change_nid_normal >= 0)
                node_set_state(node, N_NORMAL_MEMORY);

        if (arg->status_change_nid_high >= 0)
                node_set_state(node, N_HIGH_MEMORY);

        if (arg->status_change_nid >= 0)
                node_set_state(node, N_MEMORY);
}

static void __meminit resize_zone_range(struct zone *zone, unsigned long start_pfn,
                unsigned long nr_pages)
{
        unsigned long old_end_pfn = zone_end_pfn(zone);

        if (zone_is_empty(zone) || start_pfn < zone->zone_start_pfn)
                zone->zone_start_pfn = start_pfn;

        zone->spanned_pages = max(start_pfn + nr_pages, old_end_pfn) - zone->zone_start_pfn;
}

static void __meminit resize_pgdat_range(struct pglist_data *pgdat, unsigned long start_pfn,
                                     unsigned long nr_pages)
{
        unsigned long old_end_pfn = pgdat_end_pfn(pgdat);

        if (!pgdat->node_spanned_pages || start_pfn < pgdat->node_start_pfn)
                pgdat->node_start_pfn = start_pfn;

        pgdat->node_spanned_pages = max(start_pfn + nr_pages, old_end_pfn) - pgdat->node_start_pfn;

}
/*
 * Associate the pfn range with the given zone, initializing the memmaps
 * and resizing the pgdat/zone data to span the added pages. After this
 * call, all affected pages are PG_reserved.
 */
void __ref move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn,
                unsigned long nr_pages, struct vmem_altmap *altmap)
{
        struct pglist_data *pgdat = zone->zone_pgdat;
        int nid = pgdat->node_id;
        unsigned long flags;

        clear_zone_contiguous(zone);

        /* TODO Huh pgdat is irqsave while zone is not. It used to be like that before */
        pgdat_resize_lock(pgdat, &flags);
        zone_span_writelock(zone);
        if (zone_is_empty(zone))
                init_currently_empty_zone(zone, start_pfn, nr_pages);
        resize_zone_range(zone, start_pfn, nr_pages);
        zone_span_writeunlock(zone);
        resize_pgdat_range(pgdat, start_pfn, nr_pages);
        pgdat_resize_unlock(pgdat, &flags);

        /*
         * TODO now we have a visible range of pages which are not associated
         * with their zone properly. Not nice but set_pfnblock_flags_mask
         * expects the zone spans the pfn range. All the pages in the range
         * are reserved so nobody should be touching them so we should be safe
         */
        memmap_init_zone(nr_pages, nid, zone_idx(zone), start_pfn,
                        MEMMAP_HOTPLUG, altmap);

        set_zone_contiguous(zone);
}

/*
 * Returns a default kernel memory zone for the given pfn range.
 * If no kernel zone covers this pfn range it will automatically go
 * to the ZONE_NORMAL.
 */
static struct zone *default_kernel_zone_for_pfn(int nid, unsigned long start_pfn,
                unsigned long nr_pages)
{
        struct pglist_data *pgdat = NODE_DATA(nid);
        int zid;

        for (zid = 0; zid <= ZONE_NORMAL; zid++) {
                struct zone *zone = &pgdat->node_zones[zid];

                if (zone_intersects(zone, start_pfn, nr_pages))
                        return zone;
        }

        return &pgdat->node_zones[ZONE_NORMAL];
}

static inline struct zone *default_zone_for_pfn(int nid, unsigned long start_pfn,
                unsigned long nr_pages)
{
        struct zone *kernel_zone = default_kernel_zone_for_pfn(nid, start_pfn,
                        nr_pages);
        struct zone *movable_zone = &NODE_DATA(nid)->node_zones[ZONE_MOVABLE];
        bool in_kernel = zone_intersects(kernel_zone, start_pfn, nr_pages);
        bool in_movable = zone_intersects(movable_zone, start_pfn, nr_pages);

        /*
         * We inherit the existing zone in a simple case where zones do not
         * overlap in the given range
         */
        if (in_kernel ^ in_movable)
                return (in_kernel) ? kernel_zone : movable_zone;

        /*
         * If the range doesn't belong to any zone or two zones overlap in the
         * given range then we use movable zone only if movable_node is
         * enabled because we always online to a kernel zone by default.
         */
        return movable_node_enabled ? movable_zone : kernel_zone;
}

struct zone * zone_for_pfn_range(int online_type, int nid, unsigned start_pfn,
                unsigned long nr_pages)
{
        if (online_type == MMOP_ONLINE_KERNEL)
                return default_kernel_zone_for_pfn(nid, start_pfn, nr_pages);

        if (online_type == MMOP_ONLINE_MOVABLE)
                return &NODE_DATA(nid)->node_zones[ZONE_MOVABLE];

        return default_zone_for_pfn(nid, start_pfn, nr_pages);
}

int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_type)
{
        unsigned long flags;
        unsigned long onlined_pages = 0;
        struct zone *zone;
        int need_zonelists_rebuild = 0;
        int nid;
        int ret;
        struct memory_notify arg;
        struct memory_block *mem;

        mem_hotplug_begin();

        /*
         * We can't use pfn_to_nid() because nid might be stored in struct page
         * which is not yet initialized. Instead, we find nid from memory block.
         */
        mem = find_memory_block(__pfn_to_section(pfn));
        nid = mem->nid;
        put_device(&mem->dev);

        /* associate pfn range with the zone */
        zone = zone_for_pfn_range(online_type, nid, pfn, nr_pages);
        move_pfn_range_to_zone(zone, pfn, nr_pages, NULL);

        arg.start_pfn = pfn;
        arg.nr_pages = nr_pages;
        node_states_check_changes_online(nr_pages, zone, &arg);

        ret = memory_notify(MEM_GOING_ONLINE, &arg);
        ret = notifier_to_errno(ret);
        if (ret)
                goto failed_addition;

        /*
         * If this zone is not populated, then it is not in zonelist.
         * This means the page allocator ignores this zone.
         * So, zonelist must be updated after online.
         */
        if (!populated_zone(zone)) {
                need_zonelists_rebuild = 1;
                setup_zone_pageset(zone);
        }

        ret = walk_system_ram_range(pfn, nr_pages, &onlined_pages,
                online_pages_range);
        if (ret) {
                /* not a single memory resource was applicable */
                if (need_zonelists_rebuild)
                        zone_pcp_reset(zone);
                goto failed_addition;
        }

        zone->present_pages += onlined_pages;

        pgdat_resize_lock(zone->zone_pgdat, &flags);
        zone->zone_pgdat->node_present_pages += onlined_pages;
        pgdat_resize_unlock(zone->zone_pgdat, &flags);

        shuffle_zone(zone);

        node_states_set_node(nid, &arg);
        if (need_zonelists_rebuild)
                build_all_zonelists(NULL);
        else
                zone_pcp_update(zone);

        init_per_zone_wmark_min();

        kswapd_run(nid);
        kcompactd_run(nid);

        vm_total_pages = nr_free_pagecache_pages();

        writeback_set_ratelimit();

        memory_notify(MEM_ONLINE, &arg);
        mem_hotplug_done();
        return 0;

failed_addition:
        pr_debug("online_pages [mem %#010llx-%#010llx] failed\n",
                 (unsigned long long) pfn << PAGE_SHIFT,
                 (((unsigned long long) pfn + nr_pages) << PAGE_SHIFT) - 1);
        memory_notify(MEM_CANCEL_ONLINE, &arg);
        remove_pfn_range_from_zone(zone, pfn, nr_pages);
        mem_hotplug_done();
        return ret;
}
#endif /* CONFIG_MEMORY_HOTPLUG_SPARSE */

static void reset_node_present_pages(pg_data_t *pgdat)
{
        struct zone *z;

        for (z = pgdat->node_zones; z < pgdat->node_zones + MAX_NR_ZONES; z++)
                z->present_pages = 0;

        pgdat->node_present_pages = 0;
}

/* we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG */
static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
{
        struct pglist_data *pgdat;
        unsigned long start_pfn = PFN_DOWN(start);

        pgdat = NODE_DATA(nid);
        if (!pgdat) {
                pgdat = arch_alloc_nodedata(nid);
                if (!pgdat)
                        return NULL;

                pgdat->per_cpu_nodestats =
                        alloc_percpu(struct per_cpu_nodestat);
                arch_refresh_nodedata(nid, pgdat);
        } else {
                int cpu;
                /*
                 * Reset the nr_zones, order and classzone_idx before reuse.
                 * Note that kswapd will init kswapd_classzone_idx properly
                 * when it starts in the near future.
                 */
                pgdat->nr_zones = 0;
                pgdat->kswapd_order = 0;
                pgdat->kswapd_classzone_idx = 0;
                for_each_online_cpu(cpu) {
                        struct per_cpu_nodestat *p;

                        p = per_cpu_ptr(pgdat->per_cpu_nodestats, cpu);
                        memset(p, 0, sizeof(*p));
                }
        }

        /* we can use NODE_DATA(nid) from here */

        pgdat->node_id = nid;
        pgdat->node_start_pfn = start_pfn;

        /* init node's zones as empty zones, we don't have any present pages.*/
        free_area_init_core_hotplug(nid);

        /*
         * The node we allocated has no zone fallback lists. For avoiding
         * to access not-initialized zonelist, build here.
         */
        build_all_zonelists(pgdat);

        /*
         * When memory is hot-added, all the memory is in offline state. So
         * clear all zones' present_pages because they will be updated in
         * online_pages() and offline_pages().
         */
        reset_node_managed_pages(pgdat);
        reset_node_present_pages(pgdat);

        return pgdat;
}

static void rollback_node_hotadd(int nid)
{
        pg_data_t *pgdat = NODE_DATA(nid);

        arch_refresh_nodedata(nid, NULL);
        free_percpu(pgdat->per_cpu_nodestats);
        arch_free_nodedata(pgdat);
}


/**
 * try_online_node - online a node if offlined
 * @nid: the node ID
 * @start: start addr of the node
 * @set_node_online: Whether we want to online the node
 * called by cpu_up() to online a node without onlined memory.
 *
 * Returns:
 * 1 -> a new node has been allocated
 * 0 -> the node is already online
 * -ENOMEM -> the node could not be allocated
 */
static int __try_online_node(int nid, u64 start, bool set_node_online)
{
        pg_data_t *pgdat;
        int ret = 1;

        if (node_online(nid))
                return 0;

        pgdat = hotadd_new_pgdat(nid, start);
        if (!pgdat) {
                pr_err("Cannot online node %d due to NULL pgdat\n", nid);
                ret = -ENOMEM;
                goto out;
        }

        if (set_node_online) {
                node_set_online(nid);
                ret = register_one_node(nid);
                BUG_ON(ret);
        }
out:
        return ret;
}

/*
 * Users of this function always want to online/register the node
 */
int try_online_node(int nid)
{
        int ret;

        mem_hotplug_begin();
        ret =  __try_online_node(nid, 0, true);
        mem_hotplug_done();
        return ret;
}

static int check_hotplug_memory_range(u64 start, u64 size)
{
        /* memory range must be block size aligned */
        if (!size || !IS_ALIGNED(start, memory_block_size_bytes()) ||
            !IS_ALIGNED(size, memory_block_size_bytes())) {
                pr_err("Block size [%#lx] unaligned hotplug range: start %#llx, size %#llx",
                       memory_block_size_bytes(), start, size);
                return -EINVAL;
        }

        return 0;
}

static int online_memory_block(struct memory_block *mem, void *arg)
{
        return device_online(&mem->dev);
}

/*
 * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
 * and online/offline operations (triggered e.g. by sysfs).
 *
 * we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG
 */
int __ref add_memory_resource(int nid, struct resource *res)
{
        struct mhp_restrictions restrictions = {};
        u64 start, size;
        bool new_node = false;
        int ret;

        start = res->start;
        size = resource_size(res);

        ret = check_hotplug_memory_range(start, size);
        if (ret)
                return ret;

        mem_hotplug_begin();

        /*
         * Add new range to memblock so that when hotadd_new_pgdat() is called
         * to allocate new pgdat, get_pfn_range_for_nid() will be able to find
         * this new range and calculate total pages correctly.  The range will
         * be removed at hot-remove time.
         */
        memblock_add_node(start, size, nid);

        ret = __try_online_node(nid, start, false);
        if (ret < 0)
                goto error;
        new_node = ret;

        /* call arch's memory hotadd */
        ret = arch_add_memory(nid, start, size, &restrictions);
        if (ret < 0)
                goto error;

        /* create memory block devices after memory was added */
        ret = create_memory_block_devices(start, size);
        if (ret) {
                arch_remove_memory(nid, start, size, NULL);
                goto error;
        }

        if (new_node) {
                /* If sysfs file of new node can't be created, cpu on the node
                 * can't be hot-added. There is no rollback way now.
                 * So, check by BUG_ON() to catch it reluctantly..
                 * We online node here. We can't roll back from here.
                 */
                node_set_online(nid);
                ret = __register_one_node(nid);
                BUG_ON(ret);
        }

        /* link memory sections under this node.*/
        ret = link_mem_sections(nid, PFN_DOWN(start), PFN_UP(start + size - 1));
        BUG_ON(ret);

        /* create new memmap entry */
        firmware_map_add_hotplug(start, start + size, "System RAM");

        /* device_online() will take the lock when calling online_pages() */
        mem_hotplug_done();

        /* online pages if requested */
        if (memhp_auto_online)
                walk_memory_blocks(start, size, NULL, online_memory_block);

        return ret;
error:
        /* rollback pgdat allocation and others */
        if (new_node)
                rollback_node_hotadd(nid);
        memblock_remove(start, size);
        mem_hotplug_done();
        return ret;
}

/* requires device_hotplug_lock, see add_memory_resource() */
int __ref __add_memory(int nid, u64 start, u64 size)
{
        struct resource *res;
        int ret;

        res = register_memory_resource(start, size);
        if (IS_ERR(res))
                return PTR_ERR(res);

        ret = add_memory_resource(nid, res);
        if (ret < 0)
                release_memory_resource(res);
        return ret;
}

int add_memory(int nid, u64 start, u64 size)
{
        int rc;

        lock_device_hotplug();
        rc = __add_memory(nid, start, size);
        unlock_device_hotplug();

        return rc;
}
EXPORT_SYMBOL_GPL(add_memory);

#ifdef CONFIG_MEMORY_HOTREMOVE
/*
 * A free page on the buddy free lists (not the per-cpu lists) has PageBuddy
 * set and the size of the free page is given by page_order(). Using this,
 * the function determines if the pageblock contains only free pages.
 * Due to buddy contraints, a free page at least the size of a pageblock will
 * be located at the start of the pageblock
 */
static inline int pageblock_free(struct page *page)
{
        return PageBuddy(page) && page_order(page) >= pageblock_order;
}

/* Return the pfn of the start of the next active pageblock after a given pfn */
static unsigned long next_active_pageblock(unsigned long pfn)
{
        struct page *page = pfn_to_page(pfn);

        /* Ensure the starting page is pageblock-aligned */
        BUG_ON(pfn & (pageblock_nr_pages - 1));

        /* If the entire pageblock is free, move to the end of free page */
        if (pageblock_free(page)) {
                int order;
                /* be careful. we don't have locks, page_order can be changed.*/
                order = page_order(page);
                if ((order < MAX_ORDER) && (order >= pageblock_order))
                        return pfn + (1 << order);
        }

        return pfn + pageblock_nr_pages;
}

static bool is_pageblock_removable_nolock(unsigned long pfn)
{
        struct page *page = pfn_to_page(pfn);
        struct zone *zone;

        /*
         * We have to be careful here because we are iterating over memory
         * sections which are not zone aware so we might end up outside of
         * the zone but still within the section.
         * We have to take care about the node as well. If the node is offline
         * its NODE_DATA will be NULL - see page_zone.
         */
        if (!node_online(page_to_nid(page)))
                return false;

        zone = page_zone(page);
        pfn = page_to_pfn(page);
        if (!zone_spans_pfn(zone, pfn))
                return false;

        return !has_unmovable_pages(zone, page, 0, MIGRATE_MOVABLE, SKIP_HWPOISON);
}

/* Checks if this range of memory is likely to be hot-removable. */
bool is_mem_section_removable(unsigned long start_pfn, unsigned long nr_pages)
{
        unsigned long end_pfn, pfn;

        end_pfn = min(start_pfn + nr_pages,
                        zone_end_pfn(page_zone(pfn_to_page(start_pfn))));

        /* Check the starting page of each pageblock within the range */
        for (pfn = start_pfn; pfn < end_pfn; pfn = next_active_pageblock(pfn)) {
                if (!is_pageblock_removable_nolock(pfn))
                        return false;
                cond_resched();
        }

        /* All pageblocks in the memory block are likely to be hot-removable */
        return true;
}

/*
 * Confirm all pages in a range [start, end) belong to the same zone.
 * When true, return its valid [start, end).
 */
int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn,
                         unsigned long *valid_start, unsigned long *valid_end)
{
        unsigned long pfn, sec_end_pfn;
        unsigned long start, end;
        struct zone *zone = NULL;
        struct page *page;
        int i;
        for (pfn = start_pfn, sec_end_pfn = SECTION_ALIGN_UP(start_pfn + 1);
             pfn < end_pfn;
             pfn = sec_end_pfn, sec_end_pfn += PAGES_PER_SECTION) {
                /* Make sure the memory section is present first */
                if (!present_section_nr(pfn_to_section_nr(pfn)))
                        continue;
                for (; pfn < sec_end_pfn && pfn < end_pfn;
                     pfn += MAX_ORDER_NR_PAGES) {
                        i = 0;
                        /* This is just a CONFIG_HOLES_IN_ZONE check.*/
                        while ((i < MAX_ORDER_NR_PAGES) &&
                                !pfn_valid_within(pfn + i))
                                i++;
                        if (i == MAX_ORDER_NR_PAGES || pfn + i >= end_pfn)
                                continue;
                        /* Check if we got outside of the zone */
                        if (zone && !zone_spans_pfn(zone, pfn + i))
                                return 0;
                        page = pfn_to_page(pfn + i);
                        if (zone && page_zone(page) != zone)
                                return 0;
                        if (!zone)
                                start = pfn + i;
                        zone = page_zone(page);
                        end = pfn + MAX_ORDER_NR_PAGES;
                }
        }

        if (zone) {
                *valid_start = start;
                *valid_end = min(end, end_pfn);
                return 1;
        } else {
                return 0;
        }
}

/*
 * Scan pfn range [start,end) to find movable/migratable pages (LRU pages,
 * non-lru movable pages and hugepages). We scan pfn because it's much
 * easier than scanning over linked list. This function returns the pfn
 * of the first found movable page if it's found, otherwise 0.
 */
static unsigned long scan_movable_pages(unsigned long start, unsigned long end)
{
        unsigned long pfn;

        for (pfn = start; pfn < end; pfn++) {
                struct page *page, *head;
                unsigned long skip;

                if (!pfn_valid(pfn))
                        continue;
                page = pfn_to_page(pfn);
                if (PageLRU(page))
                        return pfn;
                if (__PageMovable(page))
                        return pfn;

                if (!PageHuge(page))
                        continue;
                head = compound_head(page);
                if (page_huge_active(head))
                        return pfn;
                skip = compound_nr(head) - (page - head);
                pfn += skip - 1;
        }
        return 0;
}

static struct page *new_node_page(struct page *page, unsigned long private)
{
        int nid = page_to_nid(page);
        nodemask_t nmask = node_states[N_MEMORY];

        /*
         * try to allocate from a different node but reuse this node if there
         * are no other online nodes to be used (e.g. we are offlining a part
         * of the only existing node)
         */
        node_clear(nid, nmask);
        if (nodes_empty(nmask))
                node_set(nid, nmask);

        return new_page_nodemask(page, nid, &nmask);
}

static int
do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
{
        unsigned long pfn;
        struct page *page;
        int ret = 0;
        LIST_HEAD(source);

        for (pfn = start_pfn; pfn < end_pfn; pfn++) {
                if (!pfn_valid(pfn))
                        continue;
                page = pfn_to_page(pfn);

                if (PageHuge(page)) {
                        struct page *head = compound_head(page);
                        pfn = page_to_pfn(head) + compound_nr(head) - 1;
                        isolate_huge_page(head, &source);
                        continue;
                } else if (PageTransHuge(page))
                        pfn = page_to_pfn(compound_head(page))
                                + hpage_nr_pages(page) - 1;

                /*
                 * HWPoison pages have elevated reference counts so the migration would
                 * fail on them. It also doesn't make any sense to migrate them in the
                 * first place. Still try to unmap such a page in case it is still mapped
                 * (e.g. current hwpoison implementation doesn't unmap KSM pages but keep
                 * the unmap as the catch all safety net).
                 */
                if (PageHWPoison(page)) {
                        if (WARN_ON(PageLRU(page)))
                                isolate_lru_page(page);
                        if (page_mapped(page))
                                try_to_unmap(page, TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS);
                        continue;
                }

                if (!get_page_unless_zero(page))
                        continue;
                /*
                 * We can skip free pages. And we can deal with pages on
                 * LRU and non-lru movable pages.
                 */
                if (PageLRU(page))
                        ret = isolate_lru_page(page);
                else
                        ret = isolate_movable_page(page, ISOLATE_UNEVICTABLE);
                if (!ret) { /* Success */
                        list_add_tail(&page->lru, &source);
                        if (!__PageMovable(page))
                                inc_node_page_state(page, NR_ISOLATED_ANON +
                                                    page_is_file_cache(page));

                } else {
                        pr_warn("failed to isolate pfn %lx\n", pfn);
                        dump_page(page, "isolation failed");
                }
                put_page(page);
        }
        if (!list_empty(&source)) {
                /* Allocate a new page from the nearest neighbor node */
                ret = migrate_pages(&source, new_node_page, NULL, 0,
                                        MIGRATE_SYNC, MR_MEMORY_HOTPLUG);
                if (ret) {
                        list_for_each_entry(page, &source, lru) {
                                pr_warn("migrating pfn %lx failed ret:%d ",
                                       page_to_pfn(page), ret);
                                dump_page(page, "migration failure");
                        }
                        putback_movable_pages(&source);
                }
        }

        return ret;
}

/*
 * remove from free_area[] and mark all as Reserved.
 */
static int
offline_isolated_pages_cb(unsigned long start, unsigned long nr_pages,
                        void *data)
{
        unsigned long *offlined_pages = (unsigned long *)data;

        *offlined_pages += __offline_isolated_pages(start, start + nr_pages);
        return 0;
}

/*
 * Check all pages in range, recoreded as memory resource, are isolated.
 */
static int
check_pages_isolated_cb(unsigned long start_pfn, unsigned long nr_pages,
                        void *data)
{
        return test_pages_isolated(start_pfn, start_pfn + nr_pages, true);
}

static int __init cmdline_parse_movable_node(char *p)
{
#ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
        movable_node_enabled = true;
#else
        pr_warn("movable_node parameter depends on CONFIG_HAVE_MEMBLOCK_NODE_MAP to work properly\n");
#endif
        return 0;
}
early_param("movable_node", cmdline_parse_movable_node);

/* check which state of node_states will be changed when offline memory */
static void node_states_check_changes_offline(unsigned long nr_pages,
                struct zone *zone, struct memory_notify *arg)
{
        struct pglist_data *pgdat = zone->zone_pgdat;
        unsigned long present_pages = 0;
        enum zone_type zt;

        arg->status_change_nid = NUMA_NO_NODE;
        arg->status_change_nid_normal = NUMA_NO_NODE;
        arg->status_change_nid_high = NUMA_NO_NODE;

        /*
         * Check whether node_states[N_NORMAL_MEMORY] will be changed.
         * If the memory to be offline is within the range
         * [0..ZONE_NORMAL], and it is the last present memory there,
         * the zones in that range will become empty after the offlining,
         * thus we can determine that we need to clear the node from
         * node_states[N_NORMAL_MEMORY].
         */
        for (zt = 0; zt <= ZONE_NORMAL; zt++)
                present_pages += pgdat->node_zones[zt].present_pages;
        if (zone_idx(zone) <= ZONE_NORMAL && nr_pages >= present_pages)
                arg->status_change_nid_normal = zone_to_nid(zone);

#ifdef CONFIG_HIGHMEM
        /*
         * node_states[N_HIGH_MEMORY] contains nodes which
         * have normal memory or high memory.
         * Here we add the present_pages belonging to ZONE_HIGHMEM.
         * If the zone is within the range of [0..ZONE_HIGHMEM), and
         * we determine that the zones in that range become empty,
         * we need to clear the node for N_HIGH_MEMORY.
         */
        present_pages += pgdat->node_zones[ZONE_HIGHMEM].present_pages;
        if (zone_idx(zone) <= ZONE_HIGHMEM && nr_pages >= present_pages)
                arg->status_change_nid_high = zone_to_nid(zone);
#endif

        /*
         * We have accounted the pages from [0..ZONE_NORMAL), and
         * in case of CONFIG_HIGHMEM the pages from ZONE_HIGHMEM
         * as well.
         * Here we count the possible pages from ZONE_MOVABLE.
         * If after having accounted all the pages, we see that the nr_pages
         * to be offlined is over or equal to the accounted pages,
         * we know that the node will become empty, and so, we can clear
         * it for N_MEMORY as well.
         */
        present_pages += pgdat->node_zones[ZONE_MOVABLE].present_pages;

        if (nr_pages >= present_pages)
                arg->status_change_nid = zone_to_nid(zone);
}

static void node_states_clear_node(int node, struct memory_notify *arg)
{
        if (arg->status_change_nid_normal >= 0)
                node_clear_state(node, N_NORMAL_MEMORY);

        if (arg->status_change_nid_high >= 0)
                node_clear_state(node, N_HIGH_MEMORY);

        if (arg->status_change_nid >= 0)
                node_clear_state(node, N_MEMORY);
}

static int __ref __offline_pages(unsigned long start_pfn,
                  unsigned long end_pfn)
{
        unsigned long pfn, nr_pages;
        unsigned long offlined_pages = 0;
        int ret, node, nr_isolate_pageblock;
        unsigned long flags;
        unsigned long valid_start, valid_end;
        struct zone *zone;
        struct memory_notify arg;
        char *reason;

        mem_hotplug_begin();

        /* This makes hotplug much easier...and readable.
           we assume this for now. .*/
        if (!test_pages_in_a_zone(start_pfn, end_pfn, &valid_start,
                                  &valid_end)) {
                ret = -EINVAL;
                reason = "multizone range";
                goto failed_removal;
        }

        zone = page_zone(pfn_to_page(valid_start));
        node = zone_to_nid(zone);
        nr_pages = end_pfn - start_pfn;

        /* set above range as isolated */
        ret = start_isolate_page_range(start_pfn, end_pfn,
                                       MIGRATE_MOVABLE,
                                       SKIP_HWPOISON | REPORT_FAILURE);
        if (ret < 0) {
                reason = "failure to isolate range";
                goto failed_removal;
        }
        nr_isolate_pageblock = ret;

        arg.start_pfn = start_pfn;
        arg.nr_pages = nr_pages;
        node_states_check_changes_offline(nr_pages, zone, &arg);

        ret = memory_notify(MEM_GOING_OFFLINE, &arg);
        ret = notifier_to_errno(ret);
        if (ret) {
                reason = "notifier failure";
                goto failed_removal_isolated;
        }

        do {
                for (pfn = start_pfn; pfn;) {
                        if (signal_pending(current)) {
                                ret = -EINTR;
                                reason = "signal backoff";
                                goto failed_removal_isolated;
                        }

                        cond_resched();
                        lru_add_drain_all();

                        pfn = scan_movable_pages(pfn, end_pfn);
                        if (pfn) {
                                /*
                                 * TODO: fatal migration failures should bail
                                 * out
                                 */
                                do_migrate_range(pfn, end_pfn);
                        }
                }

                /*
                 * Dissolve free hugepages in the memory block before doing
                 * offlining actually in order to make hugetlbfs's object
                 * counting consistent.
                 */
                ret = dissolve_free_huge_pages(start_pfn, end_pfn);
                if (ret) {
                        reason = "failure to dissolve huge pages";
                        goto failed_removal_isolated;
                }
                /* check again */
                ret = walk_system_ram_range(start_pfn, end_pfn - start_pfn,
                                            NULL, check_pages_isolated_cb);
        } while (ret);

        /* Ok, all of our target is isolated.
           We cannot do rollback at this point. */
        walk_system_ram_range(start_pfn, end_pfn - start_pfn,
                              &offlined_pages, offline_isolated_pages_cb);
        pr_info("Offlined Pages %ld\n", offlined_pages);
        /*
         * Onlining will reset pagetype flags and makes migrate type
         * MOVABLE, so just need to decrease the number of isolated
         * pageblocks zone counter here.
         */
        spin_lock_irqsave(&zone->lock, flags);
        zone->nr_isolate_pageblock -= nr_isolate_pageblock;
        spin_unlock_irqrestore(&zone->lock, flags);

        /* removal success */
        adjust_managed_page_count(pfn_to_page(start_pfn), -offlined_pages);
        zone->present_pages -= offlined_pages;

        pgdat_resize_lock(zone->zone_pgdat, &flags);
        zone->zone_pgdat->node_present_pages -= offlined_pages;
        pgdat_resize_unlock(zone->zone_pgdat, &flags);

        init_per_zone_wmark_min();

        if (!populated_zone(zone)) {
                zone_pcp_reset(zone);
                build_all_zonelists(NULL);
        } else
                zone_pcp_update(zone);

        node_states_clear_node(node, &arg);
        if (arg.status_change_nid >= 0) {
                kswapd_stop(node);
                kcompactd_stop(node);
        }

        vm_total_pages = nr_free_pagecache_pages();
        writeback_set_ratelimit();

        memory_notify(MEM_OFFLINE, &arg);
        remove_pfn_range_from_zone(zone, start_pfn, nr_pages);
        mem_hotplug_done();
        return 0;

failed_removal_isolated:
        undo_isolate_page_range(start_pfn, end_pfn, MIGRATE_MOVABLE);
        memory_notify(MEM_CANCEL_OFFLINE, &arg);
failed_removal:
        pr_debug("memory offlining [mem %#010llx-%#010llx] failed due to %s\n",
                 (unsigned long long) start_pfn << PAGE_SHIFT,
                 ((unsigned long long) end_pfn << PAGE_SHIFT) - 1,
                 reason);
        /* pushback to free area */
        mem_hotplug_done();
        return ret;
}

int offline_pages(unsigned long start_pfn, unsigned long nr_pages)
{
        return __offline_pages(start_pfn, start_pfn + nr_pages);
}

static int check_memblock_offlined_cb(struct memory_block *mem, void *arg)
{
        int ret = !is_memblock_offlined(mem);

        if (unlikely(ret)) {
                phys_addr_t beginpa, endpa;

                beginpa = PFN_PHYS(section_nr_to_pfn(mem->start_section_nr));
                endpa = beginpa + memory_block_size_bytes() - 1;
                pr_warn("removing memory fails, because memory [%pa-%pa] is onlined\n",
                        &beginpa, &endpa);

                return -EBUSY;
        }
        return 0;
}

static int check_cpu_on_node(pg_data_t *pgdat)
{
        int cpu;

        for_each_present_cpu(cpu) {
                if (cpu_to_node(cpu) == pgdat->node_id)
                        /*
                         * the cpu on this node isn't removed, and we can't
                         * offline this node.
                         */
                        return -EBUSY;
        }

        return 0;
}

static int check_no_memblock_for_node_cb(struct memory_block *mem, void *arg)
{
        int nid = *(int *)arg;

        /*
         * If a memory block belongs to multiple nodes, the stored nid is not
         * reliable. However, such blocks are always online (e.g., cannot get
         * offlined) and, therefore, are still spanned by the node.
         */
        return mem->nid == nid ? -EEXIST : 0;
}

/**
 * try_offline_node
 * @nid: the node ID
 *
 * Offline a node if all memory sections and cpus of the node are removed.
 *
 * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
 * and online/offline operations before this call.
 */
void try_offline_node(int nid)
{
        pg_data_t *pgdat = NODE_DATA(nid);
        int rc;

        /*
         * If the node still spans pages (especially ZONE_DEVICE), don't
         * offline it. A node spans memory after move_pfn_range_to_zone(),
         * e.g., after the memory block was onlined.
         */
        if (pgdat->node_spanned_pages)
                return;

        /*
         * Especially offline memory blocks might not be spanned by the
         * node. They will get spanned by the node once they get onlined.
         * However, they link to the node in sysfs and can get onlined later.
         */
        rc = for_each_memory_block(&nid, check_no_memblock_for_node_cb);
        if (rc)
                return;

        if (check_cpu_on_node(pgdat))
                return;

        /*
         * all memory/cpu of this node are removed, we can offline this
         * node now.
         */
        node_set_offline(nid);
        unregister_one_node(nid);
}
EXPORT_SYMBOL(try_offline_node);

static void __release_memory_resource(resource_size_t start,
                                      resource_size_t size)
{
        int ret;

        /*
         * When removing memory in the same granularity as it was added,
         * this function never fails. It might only fail if resources
         * have to be adjusted or split. We'll ignore the error, as
         * removing of memory cannot fail.
         */
        ret = release_mem_region_adjustable(&iomem_resource, start, size);
        if (ret) {
                resource_size_t endres = start + size - 1;

                pr_warn("Unable to release resource <%pa-%pa> (%d)\n",
                        &start, &endres, ret);
        }
}

static int __ref try_remove_memory(int nid, u64 start, u64 size)
{
        int rc = 0;

        BUG_ON(check_hotplug_memory_range(start, size));

        /*
         * All memory blocks must be offlined before removing memory.  Check
         * whether all memory blocks in question are offline and return error
         * if this is not the case.
         */
        rc = walk_memory_blocks(start, size, NULL, check_memblock_offlined_cb);
        if (rc)
                goto done;

        /* remove memmap entry */
        firmware_map_remove(start, start + size, "System RAM");
        memblock_free(start, size);
        memblock_remove(start, size);

        /*
         * Memory block device removal under the device_hotplug_lock is
         * a barrier against racing online attempts.
         */
        remove_memory_block_devices(start, size);

        mem_hotplug_begin();

        arch_remove_memory(nid, start, size, NULL);
        __release_memory_resource(start, size);

        try_offline_node(nid);

done:
        mem_hotplug_done();
        return rc;
}

/**
 * remove_memory
 * @nid: the node ID
 * @start: physical address of the region to remove
 * @size: size of the region to remove
 *
 * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
 * and online/offline operations before this call, as required by
 * try_offline_node().
 */
void __remove_memory(int nid, u64 start, u64 size)
{

        /*
         * trigger BUG() if some memory is not offlined prior to calling this
         * function
         */
        if (try_remove_memory(nid, start, size))
                BUG();
}

/*
 * Remove memory if every memory block is offline, otherwise return -EBUSY is
 * some memory is not offline
 */
int remove_memory(int nid, u64 start, u64 size)
{
        int rc;

        lock_device_hotplug();
        rc  = try_remove_memory(nid, start, size);
        unlock_device_hotplug();

        return rc;
}
EXPORT_SYMBOL_GPL(remove_memory);
#endif /* CONFIG_MEMORY_HOTREMOVE */