memcg: free memcg_caches slot on css offline

We need to look up a kmem_cache in ->memcg_params.memcg_caches arrays only
on allocations, so there is no need to have the array entries set until
css free - we can clear them on css offline.  This will allow us to reuse
array entries more efficiently and avoid costly array relocations.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Dave Chinner <david@fromorbit.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 28 insertions, 11 deletions

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 6087b1f..0873bcc 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -440,18 +440,8 @@ static int do_kmem_cache_shutdown(struct kmem_cache *s,
 		*need_rcu_barrier = true;
 
 #ifdef CONFIG_MEMCG_KMEM
-	if (!is_root_cache(s)) {
-		int idx;
-		struct memcg_cache_array *arr;
-
-		idx = memcg_cache_id(s->memcg_params.memcg);
-		arr = rcu_dereference_protected(s->memcg_params.root_cache->
-						memcg_params.memcg_caches,
-						lockdep_is_held(&slab_mutex));
-		BUG_ON(arr->entries[idx] != s);
-		arr->entries[idx] = NULL;
+	if (!is_root_cache(s))
 		list_del(&s->memcg_params.list);
-	}
 #endif
 	list_move(&s->list, release);
 	return 0;
@@ -499,6 +489,13 @@ void memcg_create_kmem_cache(struct mem_cgroup *memcg,
 
 	mutex_lock(&slab_mutex);
 
+	/*
+	 * The memory cgroup could have been deactivated while the cache
+	 * creation work was pending.
+	 */
+	if (!memcg_kmem_is_active(memcg))
+		goto out_unlock;
+
 	idx = memcg_cache_id(memcg);
 	arr = rcu_dereference_protected(root_cache->memcg_params.memcg_caches,
 					lockdep_is_held(&slab_mutex));
@@ -548,6 +545,26 @@ out_unlock:
 	put_online_cpus();
 }
 
+void memcg_deactivate_kmem_caches(struct mem_cgroup *memcg)
+{
+	int idx;
+	struct memcg_cache_array *arr;
+	struct kmem_cache *s;
+
+	idx = memcg_cache_id(memcg);
+
+	mutex_lock(&slab_mutex);
+	list_for_each_entry(s, &slab_caches, list) {
+		if (!is_root_cache(s))
+			continue;
+
+		arr = rcu_dereference_protected(s->memcg_params.memcg_caches,
+						lockdep_is_held(&slab_mutex));
+		arr->entries[idx] = NULL;
+	}
+	mutex_unlock(&slab_mutex);
+}
+
 void memcg_destroy_kmem_caches(struct mem_cgroup *memcg)
 {
 	LIST_HEAD(release);