mm: memcontrol: micro-optimize mem_cgroup_split_huge_fixup()

Don't call lookup_page_cgroup() when memcg is disabled.

Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 420461bcaefd..8c10d4ca9c3f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3174,7 +3174,7 @@ static inline void memcg_unregister_all_caches(struct mem_cgroup *memcg)
  */
 void mem_cgroup_split_huge_fixup(struct page *head)
 {
-        struct page_cgroup *head_pc = lookup_page_cgroup(head);
+        struct page_cgroup *head_pc;
         struct page_cgroup *pc;
         struct mem_cgroup *memcg;
         int i;
@@ -3182,6 +3182,8 @@ void mem_cgroup_split_huge_fixup(struct page *head)
         if (mem_cgroup_disabled())
                 return;
 
+        head_pc = lookup_page_cgroup(head);
+
         memcg = head_pc->mem_cgroup;
         for (i = 1; i < HPAGE_PMD_NR; i++) {
                 pc = head_pc + i;