mm: convert mm's rss stats into percpu_counter

Currently mm_struct maintains rss_stats which are updated on page fault
and the unmapping codepaths.  For page fault codepath the updates are
cached per thread with the batch of TASK_RSS_EVENTS_THRESH which is 64.
The reason for caching is performance for multithreaded applications
otherwise the rss_stats updates may become hotspot for such applications.

However this optimization comes with the cost of error margin in the rss
stats.  The rss_stats for applications with large number of threads can be
very skewed.  At worst the error margin is (nr_threads * 64) and we have a
lot of applications with 100s of threads, so the error margin can be very
high.  Internally we had to reduce TASK_RSS_EVENTS_THRESH to 32.

Recently we started seeing the unbounded errors for rss_stats for specific
applications which use TCP rx0cp.  It seems like vm_insert_pages()
codepath does not sync rss_stats at all.

This patch converts the rss_stats into percpu_counter to convert the error
margin from (nr_threads * 64) to approximately (nr_cpus ^ 2).  However
this conversion enable us to get the accurate stats for situations where
accuracy is more important than the cpu cost.

This patch does not make such tradeoffs - we can just use
percpu_counter_add_local() for the updates and percpu_counter_sum() (or
percpu_counter_sync() + percpu_counter_read) for the readers.  At the
moment the readers are either procfs interface, oom_killer and memory
reclaim which I think are not performance critical and should be ok with
slow read.  However I think we can make that change in a separate patch.

Link: https://lkml.kernel.org/r/20221024052841.3291983-1-shakeelb@google.com
Signed-off-by: Shakeel Butt <shakeelb@google.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/mm.h b/include/linux/mm.h
index f919bef..0cb4e19 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2052,40 +2052,30 @@ static inline bool get_user_page_fast_only(unsigned long addr,
  */
 static inline unsigned long get_mm_counter(struct mm_struct *mm, int member)
 {
-       long val = atomic_long_read(&mm->rss_stat.count[member]);
-
-#ifdef SPLIT_RSS_COUNTING
-       /*
-        * counter is updated in asynchronous manner and may go to minus.
-        * But it's never be expected number for users.
-        */
-       if (val < 0)
-               val = 0;
-#endif
-       return (unsigned long)val;
+       return percpu_counter_read_positive(&mm->rss_stat[member]);
 }
 
-void mm_trace_rss_stat(struct mm_struct *mm, int member, long count);
+void mm_trace_rss_stat(struct mm_struct *mm, int member);
 
 static inline void add_mm_counter(struct mm_struct *mm, int member, long value)
 {
-       long count = atomic_long_add_return(value, &mm->rss_stat.count[member]);
+       percpu_counter_add(&mm->rss_stat[member], value);
 
-       mm_trace_rss_stat(mm, member, count);
+       mm_trace_rss_stat(mm, member);
 }
 
 static inline void inc_mm_counter(struct mm_struct *mm, int member)
 {
-       long count = atomic_long_inc_return(&mm->rss_stat.count[member]);
+       percpu_counter_inc(&mm->rss_stat[member]);
 
-       mm_trace_rss_stat(mm, member, count);
+       mm_trace_rss_stat(mm, member);
 }
 
 static inline void dec_mm_counter(struct mm_struct *mm, int member)
 {
-       long count = atomic_long_dec_return(&mm->rss_stat.count[member]);
+       percpu_counter_dec(&mm->rss_stat[member]);
 
-       mm_trace_rss_stat(mm, member, count);
+       mm_trace_rss_stat(mm, member);
 }
 
 /* Optimized variant when page is already known not to be PageAnon */

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 2d5b157..e86861f 100644 (file)
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -18,6 +18,7 @@
 #include <linux/page-flags-layout.h>
 #include <linux/workqueue.h>
 #include <linux/seqlock.h>
+#include <linux/percpu_counter.h>
 
 #include <asm/mmu.h>
 
@@ -626,11 +627,7 @@ struct mm_struct {
 
                unsigned long saved_auxv[AT_VECTOR_SIZE]; /* for /proc/PID/auxv */
 
-               /*
-                * Special counters, in some configurations protected by the
-                * page_table_lock, in other configurations by being atomic.
-                */
-               struct mm_rss_stat rss_stat;
+               struct percpu_counter rss_stat[NR_MM_COUNTERS];
 
                struct linux_binfmt *binfmt;
 

diff --git a/include/linux/mm_types_task.h b/include/linux/mm_types_task.h
index 0bb4b6d..5414b5c 100644 (file)
--- a/include/linux/mm_types_task.h
+++ b/include/linux/mm_types_task.h
@@ -36,19 +36,6 @@ enum {
        NR_MM_COUNTERS
 };
 
-#if USE_SPLIT_PTE_PTLOCKS && defined(CONFIG_MMU)
-#define SPLIT_RSS_COUNTING
-/* per-thread cached information, */
-struct task_rss_stat {
-       int events;     /* for synchronization threshold */
-       int count[NR_MM_COUNTERS];
-};
-#endif /* USE_SPLIT_PTE_PTLOCKS */
-
-struct mm_rss_stat {
-       atomic_long_t count[NR_MM_COUNTERS];
-};
-
 struct page_frag {
        struct page *page;
 #if (BITS_PER_LONG > 32) || (PAGE_SIZE >= 65536)

diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h
index 8ed5fba..bde6c4c 100644 (file)
--- a/include/linux/percpu_counter.h
+++ b/include/linux/percpu_counter.h
@@ -13,7 +13,6 @@
 #include <linux/threads.h>
 #include <linux/percpu.h>
 #include <linux/types.h>
-#include <linux/gfp.h>
 
 /* percpu_counter batch for local add or sub */
 #define PERCPU_COUNTER_LOCAL_BATCH     INT_MAX

diff --git a/include/linux/sched.h b/include/linux/sched.h
index ffb6eb5..079d299 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -870,9 +870,6 @@ struct task_struct {
        struct mm_struct                *mm;
        struct mm_struct                *active_mm;
 
-#ifdef SPLIT_RSS_COUNTING
-       struct task_rss_stat            rss_stat;
-#endif
        int                             exit_state;
        int                             exit_code;
        int                             exit_signal;

diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
index 243073c..5868876 100644 (file)
--- a/include/trace/events/kmem.h
+++ b/include/trace/events/kmem.h
@@ -346,10 +346,9 @@ TRACE_MM_PAGES
 TRACE_EVENT(rss_stat,
 
        TP_PROTO(struct mm_struct *mm,
-               int member,
-               long count),
+               int member),
 
-       TP_ARGS(mm, member, count),
+       TP_ARGS(mm, member),
 
        TP_STRUCT__entry(
                __field(unsigned int, mm_id)
@@ -362,7 +361,8 @@ TRACE_EVENT(rss_stat,
                __entry->mm_id = mm_ptr_to_hash(mm);
                __entry->curr = !!(current->mm == mm);
                __entry->member = member;
-               __entry->size = (count << PAGE_SHIFT);
+               __entry->size = (percpu_counter_sum_positive(&mm->rss_stat[member])
+                                                           << PAGE_SHIFT);
        ),
 
        TP_printk("mm_id=%u curr=%d type=%s size=%ldB",

diff --git a/kernel/fork.c b/kernel/fork.c
index 08969f5..0fef202 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -753,7 +753,7 @@ static void check_mm(struct mm_struct *mm)
                         "Please make sure 'struct resident_page_types[]' is updated as well");
 
        for (i = 0; i < NR_MM_COUNTERS; i++) {
-               long x = atomic_long_read(&mm->rss_stat.count[i]);
+               long x = percpu_counter_sum(&mm->rss_stat[i]);
 
                if (unlikely(x))
                        pr_alert("BUG: Bad rss-counter state mm:%p type:%s val:%ld\n",
@@ -779,6 +779,8 @@ static void check_mm(struct mm_struct *mm)
  */
 void __mmdrop(struct mm_struct *mm)
 {
+       int i;
+
        BUG_ON(mm == &init_mm);
        WARN_ON_ONCE(mm == current->mm);
        WARN_ON_ONCE(mm == current->active_mm);
@@ -788,6 +790,9 @@ void __mmdrop(struct mm_struct *mm)
        check_mm(mm);
        put_user_ns(mm->user_ns);
        mm_pasid_drop(mm);
+
+       for (i = 0; i < NR_MM_COUNTERS; i++)
+               percpu_counter_destroy(&mm->rss_stat[i]);
        free_mm(mm);
 }
 EXPORT_SYMBOL_GPL(__mmdrop);
@@ -1107,6 +1112,8 @@ static void mm_init_uprobes_state(struct mm_struct *mm)
 static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
        struct user_namespace *user_ns)
 {
+       int i;
+
        mt_init_flags(&mm->mm_mt, MM_MT_FLAGS);
        mt_set_external_lock(&mm->mm_mt, &mm->mmap_lock);
        atomic_set(&mm->mm_users, 1);
@@ -1148,10 +1155,17 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
        if (init_new_context(p, mm))
                goto fail_nocontext;
 
+       for (i = 0; i < NR_MM_COUNTERS; i++)
+               if (percpu_counter_init(&mm->rss_stat[i], 0, GFP_KERNEL_ACCOUNT))
+                       goto fail_pcpu;
+
        mm->user_ns = get_user_ns(user_ns);
        lru_gen_init_mm(mm);
        return mm;
 
+fail_pcpu:
+       while (i > 0)
+               percpu_counter_destroy(&mm->rss_stat[--i]);
 fail_nocontext:
        mm_free_pgd(mm);
 fail_nopgd:

diff --git a/mm/memory.c b/mm/memory.c
index 7826143..e0555dd 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -162,58 +162,11 @@ static int __init init_zero_pfn(void)
 }
 early_initcall(init_zero_pfn);
 
-void mm_trace_rss_stat(struct mm_struct *mm, int member, long count)
+void mm_trace_rss_stat(struct mm_struct *mm, int member)
 {
-       trace_rss_stat(mm, member, count);
+       trace_rss_stat(mm, member);
 }
 
-#if defined(SPLIT_RSS_COUNTING)
-
-void sync_mm_rss(struct mm_struct *mm)
-{
-       int i;
-
-       for (i = 0; i < NR_MM_COUNTERS; i++) {
-               if (current->rss_stat.count[i]) {
-                       add_mm_counter(mm, i, current->rss_stat.count[i]);
-                       current->rss_stat.count[i] = 0;
-               }
-       }
-       current->rss_stat.events = 0;
-}
-
-static void add_mm_counter_fast(struct mm_struct *mm, int member, int val)
-{
-       struct task_struct *task = current;
-
-       if (likely(task->mm == mm))
-               task->rss_stat.count[member] += val;
-       else
-               add_mm_counter(mm, member, val);
-}
-#define inc_mm_counter_fast(mm, member) add_mm_counter_fast(mm, member, 1)
-#define dec_mm_counter_fast(mm, member) add_mm_counter_fast(mm, member, -1)
-
-/* sync counter once per 64 page faults */
-#define TASK_RSS_EVENTS_THRESH (64)
-static void check_sync_rss_stat(struct task_struct *task)
-{
-       if (unlikely(task != current))
-               return;
-       if (unlikely(task->rss_stat.events++ > TASK_RSS_EVENTS_THRESH))
-               sync_mm_rss(task->mm);
-}
-#else /* SPLIT_RSS_COUNTING */
-
-#define inc_mm_counter_fast(mm, member) inc_mm_counter(mm, member)
-#define dec_mm_counter_fast(mm, member) dec_mm_counter(mm, member)
-
-static void check_sync_rss_stat(struct task_struct *task)
-{
-}
-
-#endif /* SPLIT_RSS_COUNTING */
-
 /*
  * Note: this doesn't free the actual pages themselves. That
  * has been handled earlier when unmapping all the memory regions.
@@ -1857,7 +1810,7 @@ static int insert_page_into_pte_locked(struct vm_area_struct *vma, pte_t *pte,
                return -EBUSY;
        /* Ok, finally just insert the thing.. */
        get_page(page);
-       inc_mm_counter_fast(vma->vm_mm, mm_counter_file(page));
+       inc_mm_counter(vma->vm_mm, mm_counter_file(page));
        page_add_file_rmap(page, vma, false);
        set_pte_at(vma->vm_mm, addr, pte, mk_pte(page, prot));
        return 0;
@@ -3153,12 +3106,11 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
        if (likely(pte_same(*vmf->pte, vmf->orig_pte))) {
                if (old_page) {
                        if (!PageAnon(old_page)) {
-                               dec_mm_counter_fast(mm,
-                                               mm_counter_file(old_page));
-                               inc_mm_counter_fast(mm, MM_ANONPAGES);
+                               dec_mm_counter(mm, mm_counter_file(old_page));
+                               inc_mm_counter(mm, MM_ANONPAGES);
                        }
                } else {
-                       inc_mm_counter_fast(mm, MM_ANONPAGES);
+                       inc_mm_counter(mm, MM_ANONPAGES);
                }
                flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
                entry = mk_pte(new_page, vma->vm_page_prot);
@@ -3965,8 +3917,8 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
        if (should_try_to_free_swap(folio, vma, vmf->flags))
                folio_free_swap(folio);
 
-       inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
-       dec_mm_counter_fast(vma->vm_mm, MM_SWAPENTS);
+       inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
+       dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
        pte = mk_pte(page, vma->vm_page_prot);
 
        /*
@@ -4146,7 +4098,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
                return handle_userfault(vmf, VM_UFFD_MISSING);
        }
 
-       inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
+       inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
        page_add_new_anon_rmap(page, vma, vmf->address);
        lru_cache_add_inactive_or_unevictable(page, vma);
 setpte:
@@ -4336,11 +4288,11 @@ void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr)
                entry = pte_mkuffd_wp(pte_wrprotect(entry));
        /* copy-on-write page */
        if (write && !(vma->vm_flags & VM_SHARED)) {
-               inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
+               inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
                page_add_new_anon_rmap(page, vma, addr);
                lru_cache_add_inactive_or_unevictable(page, vma);
        } else {
-               inc_mm_counter_fast(vma->vm_mm, mm_counter_file(page));
+               inc_mm_counter(vma->vm_mm, mm_counter_file(page));
                page_add_file_rmap(page, vma, false);
        }
        set_pte_at(vma->vm_mm, addr, vmf->pte, entry);
@@ -5192,9 +5144,6 @@ vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
        count_vm_event(PGFAULT);
        count_memcg_event_mm(vma->vm_mm, PGFAULT);
 
-       /* do counter updates before entering really critical section. */
-       check_sync_rss_stat(current);
-
        if (!arch_vma_access_permitted(vma, flags & FAULT_FLAG_WRITE,
                                            flags & FAULT_FLAG_INSTRUCTION,
                                            flags & FAULT_FLAG_REMOTE))