memcg, slab: cleanup memcg cache creation

This patch cleans up the memcg cache creation path as follows:

- Move memcg cache name creation to a separate function to be called
  from kmem_cache_create_memcg().  This allows us to get rid of the mutex
  protecting the temporary buffer used for the name formatting, because
  the whole cache creation path is protected by the slab_mutex.

- Get rid of memcg_create_kmem_cache().  This function serves as a proxy
  to kmem_cache_create_memcg().  After separating the cache name creation
  path, it would be reduced to a function call, so let's inline it.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Glauber Costa <glommer@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 39 insertions, 50 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e33b1d09eb1f..32c7342df4bf 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3094,6 +3094,29 @@ int memcg_update_cache_size(struct kmem_cache *s, int num_groups)
         return 0;
 }
 
+char *memcg_create_cache_name(struct mem_cgroup *memcg,
+                              struct kmem_cache *root_cache)
+{
+        static char *buf = NULL;
+
+        /*
+         * We need a mutex here to protect the shared buffer. Since this is
+         * expected to be called only on cache creation, we can employ the
+         * slab_mutex for that purpose.
+         */
+        lockdep_assert_held(&slab_mutex);
+
+        if (!buf) {
+                buf = kmalloc(NAME_MAX + 1, GFP_KERNEL);
+                if (!buf)
+                        return NULL;
+        }
+
+        cgroup_name(memcg->css.cgroup, buf, NAME_MAX + 1);
+        return kasprintf(GFP_KERNEL, "%s(%d:%s)", root_cache->name,
+                         memcg_cache_id(memcg), buf);
+}
+
 int memcg_alloc_cache_params(struct mem_cgroup *memcg, struct kmem_cache *s,
                              struct kmem_cache *root_cache)
 {
@@ -3298,46 +3321,6 @@ void mem_cgroup_destroy_cache(struct kmem_cache *cachep)
         schedule_work(&cachep->memcg_params->destroy);
 }
 
-static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
-                                                  struct kmem_cache *s)
-{
-        struct kmem_cache *new = NULL;
-        static char *tmp_path = NULL, *tmp_name = NULL;
-        static DEFINE_MUTEX(mutex);     /* protects tmp_name */
-
-        BUG_ON(!memcg_can_account_kmem(memcg));
-
-        mutex_lock(&mutex);
-        /*
-         * kmem_cache_create_memcg duplicates the given name and
-         * cgroup_name for this name requires RCU context.
-         * This static temporary buffer is used to prevent from
-         * pointless shortliving allocation.
-         */
-        if (!tmp_path || !tmp_name) {
-                if (!tmp_path)
-                        tmp_path = kmalloc(PATH_MAX, GFP_KERNEL);
-                if (!tmp_name)
-                        tmp_name = kmalloc(NAME_MAX + 1, GFP_KERNEL);
-                if (!tmp_path || !tmp_name)
-                        goto out;
-        }
-
-        cgroup_name(memcg->css.cgroup, tmp_name, NAME_MAX + 1);
-        snprintf(tmp_path, PATH_MAX, "%s(%d:%s)", s->name,
-                 memcg_cache_id(memcg), tmp_name);
-
-        new = kmem_cache_create_memcg(memcg, tmp_path, s->object_size, s->align,
-                                      (s->flags & ~SLAB_PANIC), s->ctor, s);
-        if (new)
-                new->allocflags |= __GFP_KMEMCG;
-        else
-                new = s;
-out:
-        mutex_unlock(&mutex);
-        return new;
-}
-
 void kmem_cache_destroy_memcg_children(struct kmem_cache *s)
 {
         struct kmem_cache *c;
@@ -3384,12 +3367,6 @@ void kmem_cache_destroy_memcg_children(struct kmem_cache *s)
         mutex_unlock(&activate_kmem_mutex);
 }
 
-struct create_work {
-        struct mem_cgroup *memcg;
-        struct kmem_cache *cachep;
-        struct work_struct work;
-};
-
 static void mem_cgroup_destroy_all_caches(struct mem_cgroup *memcg)
 {
         struct kmem_cache *cachep;
@@ -3407,13 +3384,25 @@ static void mem_cgroup_destroy_all_caches(struct mem_cgroup *memcg)
         mutex_unlock(&memcg->slab_caches_mutex);
 }
 
+struct create_work {
+        struct mem_cgroup *memcg;
+        struct kmem_cache *cachep;
+        struct work_struct work;
+};
+
 static void memcg_create_cache_work_func(struct work_struct *w)
 {
-        struct create_work *cw;
+        struct create_work *cw = container_of(w, struct create_work, work);
+        struct mem_cgroup *memcg = cw->memcg;
+        struct kmem_cache *cachep = cw->cachep;
+        struct kmem_cache *new;
 
-        cw = container_of(w, struct create_work, work);
-        memcg_create_kmem_cache(cw->memcg, cw->cachep);
-        css_put(&cw->memcg->css);
+        new = kmem_cache_create_memcg(memcg, cachep->name,
+                        cachep->object_size, cachep->align,
+                        cachep->flags & ~SLAB_PANIC, cachep->ctor, cachep);
+        if (new)
+                new->allocflags |= __GFP_KMEMCG;
+        css_put(&memcg->css);
         kfree(cw);
 }