memcg, slab: clean up memcg cache initialization/destruction

Currently, we have rather a messy function set relating to per-memcg
kmem cache initialization/destruction.

Per-memcg caches are created in memcg_create_kmem_cache().  This
function calls kmem_cache_create_memcg() to allocate and initialize a
kmem cache and then "registers" the new cache in the
memcg_params::memcg_caches array of the parent cache.

During its work-flow, kmem_cache_create_memcg() executes the following
memcg-related functions:

 - memcg_alloc_cache_params(), to initialize memcg_params of the newly
   created cache;
 - memcg_cache_list_add(), to add the new cache to the memcg_slab_caches
   list.

On the other hand, kmem_cache_destroy() called on a cache destruction
only calls memcg_release_cache(), which does all the work: it cleans the
reference to the cache in its parent's memcg_params::memcg_caches,
removes the cache from the memcg_slab_caches list, and frees
memcg_params.

Such an inconsistency between destruction and initialization paths make
the code difficult to read, so let's clean this up a bit.

This patch moves all the code relating to registration of per-memcg
caches (adding to memcg list, setting the pointer to a cache from its
parent) to the newly created memcg_register_cache() and
memcg_unregister_cache() functions making the initialization and
destruction paths look symmetrical.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Glauber Costa <glommer@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 33 insertions, 36 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b8ebe71f872d..739383cd3f70 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3095,16 +3095,6 @@ static void memcg_uncharge_kmem(struct mem_cgroup *memcg, u64 size)
                 css_put(&memcg->css);
 }
 
-void memcg_cache_list_add(struct mem_cgroup *memcg, struct kmem_cache *cachep)
-{
-        if (!memcg)
-                return;
-
-        mutex_lock(&memcg->slab_caches_mutex);
-        list_add(&cachep->memcg_params->list, &memcg->memcg_slab_caches);
-        mutex_unlock(&memcg->slab_caches_mutex);
-}
-
 /*
  * helper for acessing a memcg's index. It will be used as an index in the
  * child cache array in kmem_cache, and also to derive its name. This function
@@ -3265,21 +3255,41 @@ void memcg_free_cache_params(struct kmem_cache *s)
         kfree(s->memcg_params);
 }
 
-void memcg_release_cache(struct kmem_cache *s)
+void memcg_register_cache(struct kmem_cache *s)
 {
         struct kmem_cache *root;
         struct mem_cgroup *memcg;
         int id;
 
+        if (is_root_cache(s))
+                return;
+
+        root = s->memcg_params->root_cache;
+        memcg = s->memcg_params->memcg;
+        id = memcg_cache_id(memcg);
+
+        css_get(&memcg->css);
+
+        mutex_lock(&memcg->slab_caches_mutex);
+        list_add(&s->memcg_params->list, &memcg->memcg_slab_caches);
+        mutex_unlock(&memcg->slab_caches_mutex);
+
+        root->memcg_params->memcg_caches[id] = s;
         /*
-         * This happens, for instance, when a root cache goes away before we
-         * add any memcg.
+         * the readers won't lock, make sure everybody sees the updated value,
+         * so they won't put stuff in the queue again for no reason
          */
-        if (!s->memcg_params)
-                return;
+        wmb();
+}
 
-        if (s->memcg_params->is_root_cache)
-                goto out;
+void memcg_unregister_cache(struct kmem_cache *s)
+{
+        struct kmem_cache *root;
+        struct mem_cgroup *memcg;
+        int id;
+
+        if (is_root_cache(s))
+                return;
 
         memcg = s->memcg_params->memcg;
         id  = memcg_cache_id(memcg);
@@ -3292,8 +3302,6 @@ void memcg_release_cache(struct kmem_cache *s)
         mutex_unlock(&memcg->slab_caches_mutex);
 
         css_put(&memcg->css);
-out:
-        memcg_free_cache_params(s);
 }
 
 /*
@@ -3451,26 +3459,13 @@ static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
 
         mutex_lock(&memcg_cache_mutex);
         new_cachep = cache_from_memcg_idx(cachep, idx);
-        if (new_cachep) {
-                css_put(&memcg->css);
+        if (new_cachep)
                 goto out;
-        }
 
         new_cachep = kmem_cache_dup(memcg, cachep);
-        if (new_cachep == NULL) {
+        if (new_cachep == NULL)
                 new_cachep = cachep;
-                css_put(&memcg->css);
-                goto out;
-        }
-
-        atomic_set(&new_cachep->memcg_params->nr_pages , 0);
 
-        cachep->memcg_params->memcg_caches[idx] = new_cachep;
-        /*
-         * the readers won't lock, make sure everybody sees the updated value,
-         * so they won't put stuff in the queue again for no reason
-         */
-        wmb();
 out:
         mutex_unlock(&memcg_cache_mutex);
         return new_cachep;
@@ -3550,6 +3545,7 @@ static void memcg_create_cache_work_func(struct work_struct *w)
 
         cw = container_of(w, struct create_work, work);
         memcg_create_kmem_cache(cw->memcg, cw->cachep);
+        css_put(&cw->memcg->css);
         kfree(cw);
 }
 
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 70f9e249ac30..db24ec48b946 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -215,7 +215,7 @@ kmem_cache_create_memcg(struct mem_cgroup *memcg, const char *name, size_t size,
 
         s->refcount = 1;
         list_add(&s->list, &slab_caches);
-        memcg_cache_list_add(memcg, s);
+        memcg_register_cache(s);
 
 out_unlock:
         mutex_unlock(&slab_mutex);
@@ -265,7 +265,8 @@ void kmem_cache_destroy(struct kmem_cache *s)
                         if (s->flags & SLAB_DESTROY_BY_RCU)
                                 rcu_barrier();
 
-                        memcg_release_cache(s);
+                        memcg_unregister_cache(s);
+                        memcg_free_cache_params(s);
                         kfree(s->name);
                         kmem_cache_free(kmem_cache, s);
                 } else {