1 files changed, 42 insertions, 20 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8afed2819b8f..df1e180f6c30 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1910,32 +1910,59 @@ bool mem_cgroup_handle_oom(struct mem_cgroup *memcg, gfp_t mask, int order)
  * 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_page_cgroup(). Because we already hold
+         * rcu_read_lock(), any calls to move_account will be delayed until
+         * rcu_read_unlock() if mem_cgroup_stealed() == true.
+         */
+        if (!mem_cgroup_stealed(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_page_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);
-        bool need_unlock = false;
         unsigned long uninitialized_var(flags);
 
         if (mem_cgroup_disabled())
                 return;
-again:
-        rcu_read_lock();
+
         memcg = pc->mem_cgroup;
         if (unlikely(!memcg || !PageCgroupUsed(pc)))
-                goto out;
-        /* pc->mem_cgroup is unstable ? */
-        if (unlikely(mem_cgroup_stealed(memcg))) {
-                /* take a lock against to access pc->mem_cgroup */
-                move_lock_mem_cgroup(memcg, &flags);
-                if (memcg != pc->mem_cgroup || !PageCgroupUsed(pc)) {
-                        move_unlock_mem_cgroup(memcg, &flags);
-                        rcu_read_unlock();
-                        goto again;
-                }
-                need_unlock = true;
-        }
+                return;
 
         switch (idx) {
         case MEMCG_NR_FILE_MAPPED:
@@ -1950,11 +1977,6 @@ again:
         }
 
         this_cpu_add(memcg->stat->count[idx], val);
-
-out:
-        if (unlikely(need_unlock))
-                move_unlock_mem_cgroup(memcg, &flags);
-        rcu_read_unlock();
 }
 
 /*