mm, memcg: move all oom handling to memcontrol.c

By globally defining check_panic_on_oom(), the memcg oom handler can be
moved entirely to mm/memcontrol.c.  This removes the ugly #ifdef in the
oom killer and cleans up the code.

Signed-off-by: David Rientjes <rientjes@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index a3a32ae..1986008 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -556,8 +556,8 @@
 /*
  * Determines whether the kernel must panic because of the panic_on_oom sysctl.
  */
-static void check_panic_on_oom(enum oom_constraint constraint, gfp_t gfp_mask,
-				int order, const nodemask_t *nodemask)
+void check_panic_on_oom(enum oom_constraint constraint, gfp_t gfp_mask,
+			int order, const nodemask_t *nodemask)
 {
 	if (likely(!sysctl_panic_on_oom))
 		return;
@@ -575,25 +575,6 @@
 		sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
 }
 
-#ifdef CONFIG_MEMCG
-void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
-			      int order)
-{
-	/*
-	 * If current has a pending SIGKILL, then automatically select it.  The
-	 * goal is to allow it to allocate so that it may quickly exit and free
-	 * its memory.
-	 */
-	if (fatal_signal_pending(current)) {
-		set_thread_flag(TIF_MEMDIE);
-		return;
-	}
-
-	check_panic_on_oom(CONSTRAINT_MEMCG, gfp_mask, order, NULL);
-	__mem_cgroup_out_of_memory(memcg, gfp_mask, order);
-}
-#endif
-
 static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
 
 int register_oom_notifier(struct notifier_block *nb)