memcg: correct comments for __mem_cgroup_begin_update_page_stat

Signed-off-by: Qiang Huang <h.huangqiang@huawei.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -2276,12 +2276,11 @@ cleanup:
 }
 
 /*
- * Currently used to update mapped file statistics, but the routine can be
+ * Used to update mapped file or writeback or other statistics.
- * generalized to update other statistics as well.
  *
  * Notes: Race condition
  *
- * We usually use page_cgroup_lock() for accessing page_cgroup member but
+ * We usually use lock_page_cgroup() for accessing page_cgroup member but
  * it tends to be costly. But considering some conditions, we doesn't need
  * to do so _always_.
  *
@@ -2295,8 +2294,8 @@ cleanup:
  * 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
+ * small, we check memcg->moving_account and detect there are possibility
- * If there is, we take a lock.
+ * of race or not. If there is, we take a lock.
  */
 
 void __mem_cgroup_begin_update_page_stat(struct page *page,