memcg: remove impossible conditional when committing

No callsite ever passes a NULL pointer for a struct mem_cgroup * to the
committing function.  There is no need to check for it.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -2118,10 +2118,6 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
 {
 	int nr_pages = page_size >> PAGE_SHIFT;
 
-	/* try_charge() can return NULL to *memcg, taking care of it. */
-	if (!mem)
-		return;
-
 	lock_page_cgroup(pc);
 	if (unlikely(PageCgroupUsed(pc))) {
 		unlock_page_cgroup(pc);