memcg: remove activate_kmem_mutex

The activate_kmem_mutex is used to serialize memcg.kmem.limit updates, but
we already serialize them with memcg_limit_mutex so let's remove the
former.
Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -2627,8 +2627,6 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg,
  */
 static DEFINE_MUTEX(memcg_slab_mutex);
 
-static DEFINE_MUTEX(activate_kmem_mutex);
-
 /*
  * This is a bit cumbersome, but it is rarely used and avoids a backpointer
  * in the memcg_cache_params struct.
@@ -3747,9 +3745,8 @@ static u64 mem_cgroup_read_u64(struct cgroup_subsys_state *css,
 }
 
 #ifdef CONFIG_MEMCG_KMEM
-/* should be called with activate_kmem_mutex held */
-static int __memcg_activate_kmem(struct mem_cgroup *memcg,
-				 unsigned long nr_pages)
+static int memcg_activate_kmem(struct mem_cgroup *memcg,
+			       unsigned long nr_pages)
 {
 	int err = 0;
 	int memcg_id;
@@ -3811,17 +3808,6 @@ static int __memcg_activate_kmem(struct mem_cgroup *memcg,
 	return err;
 }
 
-static int memcg_activate_kmem(struct mem_cgroup *memcg,
-			       unsigned long nr_pages)
-{
-	int ret;
-
-	mutex_lock(&activate_kmem_mutex);
-	ret = __memcg_activate_kmem(memcg, nr_pages);
-	mutex_unlock(&activate_kmem_mutex);
-	return ret;
-}
-
 static int memcg_update_kmem_limit(struct mem_cgroup *memcg,
 				   unsigned long limit)
 {
@@ -3844,14 +3830,14 @@ static int memcg_propagate_kmem(struct mem_cgroup *memcg)
 	if (!parent)
 		return 0;
 
-	mutex_lock(&activate_kmem_mutex);
+	mutex_lock(&memcg_limit_mutex);
 	/*
 	 * If the parent cgroup is not kmem-active now, it cannot be activated
 	 * after this point, because it has at least one child already.
 	 */
 	if (memcg_kmem_is_active(parent))
-		ret = __memcg_activate_kmem(memcg, PAGE_COUNTER_MAX);
-	mutex_unlock(&activate_kmem_mutex);
+		ret = memcg_activate_kmem(memcg, PAGE_COUNTER_MAX);
+	mutex_unlock(&memcg_limit_mutex);
 	return ret;
 }
 #else