Fix an incorrect condition in memcg lru manipulation

The PageAcctLRU bit itself does not mean a lot without checking
if the mem cgroup is the same as the root cgroup. This patch
fixes a left over from the previous versions.
Reported-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/memcontrol.c

@@ -414,7 +414,7 @@ void mem_cgroup_rotate_lru_list(struct page *page, enum lru_list lru)
 	 */
 	smp_rmb();
 	/* unused or root page is not rotated. */
-	if (!PageCgroupUsed(pc) || PageCgroupAcctLRU(pc))
+	if (!PageCgroupUsed(pc) || mem_cgroup_is_root(pc->mem_cgroup))
 		return;
 	mz = page_cgroup_zoneinfo(pc);
 	list_move(&pc->lru, &mz->lists[lru]);