slub: move synchronize_sched out of slab_mutex on shrink

synchronize_sched() is a heavy operation and calling it per each cache
owned by a memory cgroup being destroyed may take quite some time.  What
is worse, it's currently called under the slab_mutex, stalling all works
doing cache creation/destruction.

Actually, there isn't much point in calling synchronize_sched() for each
cache - it's enough to call it just once - after setting cpu_partial for
all caches and before shrinking them.  This way, we can also move it out
of the slab_mutex, which we have to hold for iterating over the slab
cache list.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=172991
Link: http://lkml.kernel.org/r/0a10d71ecae3db00fb4421bcd3f82bcc911f4be4.1475329751.git.vdavydov.dev@gmail.com
Signed-off-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Reported-by: Doug Smythies <dsmythies@telus.net>
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 17 deletions

diff --git a/mm/slub.c b/mm/slub.c
index 2b3e740609e9..4a861f265cd7 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3883,7 +3883,7 @@ EXPORT_SYMBOL(kfree);
  * being allocated from last increasing the chance that the last objects
  * are freed in them.
  */
-int __kmem_cache_shrink(struct kmem_cache *s, bool deactivate)
+int __kmem_cache_shrink(struct kmem_cache *s)
 {
         int node;
         int i;
@@ -3895,21 +3895,6 @@ int __kmem_cache_shrink(struct kmem_cache *s, bool deactivate)
         unsigned long flags;
         int ret = 0;
 
-        if (deactivate) {
-                /*
-                 * Disable empty slabs caching. Used to avoid pinning offline
-                 * memory cgroups by kmem pages that can be freed.
-                 */
-                s->cpu_partial = 0;
-                s->min_partial = 0;
-
-                /*
-                 * s->cpu_partial is checked locklessly (see put_cpu_partial),
-                 * so we have to make sure the change is visible.
-                 */
-                synchronize_sched();
-        }
-
         flush_all(s);
         for_each_kmem_cache_node(s, node, n) {
                 INIT_LIST_HEAD(&discard);
@@ -3966,7 +3951,7 @@ static int slab_mem_going_offline_callback(void *arg)
 
         mutex_lock(&slab_mutex);
         list_for_each_entry(s, &slab_caches, list)
-                __kmem_cache_shrink(s, false);
+                __kmem_cache_shrink(s);
         mutex_unlock(&slab_mutex);
 
         return 0;