memcg, slab: separate memcg vs root cache creation paths

Memcg-awareness turned kmem_cache_create() into a dirty interweaving of
memcg-only and except-for-memcg calls.  To clean this up, let's move the
code responsible for memcg cache creation to a separate function.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Glauber Costa <glommer@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 32c7342..451523c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3395,13 +3395,8 @@
 	struct create_work *cw = container_of(w, struct create_work, work);
 	struct mem_cgroup *memcg = cw->memcg;
 	struct kmem_cache *cachep = cw->cachep;
-	struct kmem_cache *new;
 
-	new = kmem_cache_create_memcg(memcg, cachep->name,
-			cachep->object_size, cachep->align,
-			cachep->flags & ~SLAB_PANIC, cachep->ctor, cachep);
-	if (new)
-		new->allocflags |= __GFP_KMEMCG;
+	kmem_cache_create_memcg(memcg, cachep);
 	css_put(&memcg->css);
 	kfree(cw);
 }