[Devel] [PATCH v2 28/29] slub: track all children of a kmem cache

[Glauber Costa]

When we destroy a cache (like for instance, if we're unloading a module)
we need to go through the list of memcg caches and destroy them as well.

The caches are expected to be empty by themselves, so nothing is changed
here. All previous guarantees are kept and no new guarantees are given.

So given all memcg caches are expected to be empty - even though they are
likely to be hanging around in the system, we just need to scan a list of
sibling caches, and destroy each one of them.

This is very similar to the work done by Suleiman for the slab.

Signed-off-by: Glauber Costa <glommer at parallels.com>
CC: Christoph Lameter <cl at linux.com>
CC: Pekka Enberg <penberg at cs.helsinki.fi>
CC: Michal Hocko <mhocko at suse.cz>
CC: Kamezawa Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com>
CC: Johannes Weiner <hannes at cmpxchg.org>
CC: Suleiman Souhlal <suleiman at google.com>
---
 mm/slub.c |   61 +++++++++++++++++++++++++++++++++++++++++++++++--------------
 1 files changed, 47 insertions(+), 14 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index afe29ef..cfa6295 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3267,6 +3267,20 @@ static inline int kmem_cache_close(struct kmem_cache *s)
 	return 0;
 }
 
+void kmem_cache_destroy_unlocked(struct kmem_cache *s)
+{
+	mem_cgroup_release_cache(s);
+	if (kmem_cache_close(s)) {
+		printk(KERN_ERR "SLUB %s: %s called for cache that "
+			"still has objects.\n", s->name, __func__);
+		dump_stack();
+	}
+
+	if (s->flags & SLAB_DESTROY_BY_RCU)
+		rcu_barrier();
+	sysfs_slab_remove(s);
+}
+
 /*
  * Close a cache and release the kmem_cache structure
  * (must be used for caches created using kmem_cache_create)
@@ -3275,24 +3289,41 @@ void kmem_cache_destroy(struct kmem_cache *s)
 {
 	down_write(&slub_lock);
 	s->refcount--;
-	if (!s->refcount) {
-		list_del(&s->list);
+
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
-		/* Not a memcg cache */
-		if (s->memcg_params.id != -1) {
-			mem_cgroup_release_cache(s);
-			mem_cgroup_flush_cache_create_queue();
+	/* Not a memcg cache */
+	if (s->memcg_params.id != -1) {
+		struct mem_cgroup_cache_params *p, *tmp, *this;
+		struct kmem_cache *c;
+		int id = s->memcg_params.id;
+
+		this = &s->memcg_params;
+		mem_cgroup_flush_cache_create_queue();
+		list_for_each_entry_safe(p, tmp, &this->sibling_list, sibling_list) {
+			c = container_of(p, struct kmem_cache, memcg_params);
+			/* We never added the main cache to the sibling list */
+			if (WARN_ON(c == s))
+				continue;
+
+			c->refcount--;
+			if (c->refcount)
+				continue;
+
+			list_del(&c->list);
+			list_del(&c->memcg_params.sibling_list);
+			s->refcount--; /* parent reference */
+			up_write(&slub_lock);
+			mem_cgroup_remove_child_kmem_cache(c, id);
+			kmem_cache_destroy_unlocked(c);
+			down_write(&slub_lock);
 		}
+	}
 #endif
+
+	if (!s->refcount) {
+		list_del(&s->list);
 		up_write(&slub_lock);
-		if (kmem_cache_close(s)) {
-			printk(KERN_ERR "SLUB %s: %s called for cache that "
-				"still has objects.\n", s->name, __func__);
-			dump_stack();
-		}
-		if (s->flags & SLAB_DESTROY_BY_RCU)
-			rcu_barrier();
-		sysfs_slab_remove(s);
+		kmem_cache_destroy_unlocked(s);
 	} else
 		up_write(&slub_lock);
 }
@@ -4150,6 +4181,8 @@ struct kmem_cache *kmem_cache_dup(struct mem_cgroup *memcg,
 	 */
 	if (new) {
 		down_write(&slub_lock);
+		list_add(&new->memcg_params.sibling_list,
+			 &s->memcg_params.sibling_list);
 		s->refcount++;
 		up_write(&slub_lock);
 	}
-- 
1.7.7.6