+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_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_page_cgroup().
+ */
+ move_unlock_mem_cgroup(pc->mem_cgroup, flags);
+}
+