memcg: get rid of memcg_create_cache_name

Instead of calling back to memcontrol.c from kmem_cache_create_memcg in
order to just create the name of a per memcg cache, let's allocate it in
place.  We only need to pass the memcg name to kmem_cache_create_memcg for
that - everything else can be done in slab_common.c.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 16 insertions, 29 deletions

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 1fa23244fe37..dfc2929a3877 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -492,8 +492,6 @@ void __memcg_kmem_uncharge_pages(struct page *page, int order);
 
 int memcg_cache_id(struct mem_cgroup *memcg);
 
-char *memcg_create_cache_name(struct mem_cgroup *memcg,
-                              struct kmem_cache *root_cache);
 int memcg_alloc_cache_params(struct mem_cgroup *memcg, struct kmem_cache *s,
                              struct kmem_cache *root_cache);
 void memcg_free_cache_params(struct kmem_cache *s);
diff --git a/include/linux/slab.h b/include/linux/slab.h
index ecbec9ccb80d..86e5b26fbdab 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -117,7 +117,8 @@ struct kmem_cache *kmem_cache_create(const char *, size_t, size_t,
                         void (*)(void *));
 #ifdef CONFIG_MEMCG_KMEM
 struct kmem_cache *kmem_cache_create_memcg(struct mem_cgroup *,
-                                           struct kmem_cache *);
+                                           struct kmem_cache *,
+                                           const char *);
 #endif
 void kmem_cache_destroy(struct kmem_cache *);
 int kmem_cache_shrink(struct kmem_cache *);
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 971d7b643f6e..7df7f599e3df 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3095,29 +3095,6 @@ 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;
-
-        /*
-         * 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)
 {
@@ -3158,6 +3135,7 @@ void memcg_free_cache_params(struct kmem_cache *s)
 static void memcg_kmem_create_cache(struct mem_cgroup *memcg,
                                     struct kmem_cache *root_cache)
 {
+        static char *memcg_name_buf;    /* protected by memcg_slab_mutex */
         struct kmem_cache *cachep;
         int id;
 
@@ -3173,7 +3151,14 @@ static void memcg_kmem_create_cache(struct mem_cgroup *memcg,
         if (cache_from_memcg_idx(root_cache, id))
                 return;
 
-        cachep = kmem_cache_create_memcg(memcg, root_cache);
+        if (!memcg_name_buf) {
+                memcg_name_buf = kmalloc(NAME_MAX + 1, GFP_KERNEL);
+                if (!memcg_name_buf)
+                        return;
+        }
+
+        cgroup_name(memcg->css.cgroup, memcg_name_buf, NAME_MAX + 1);
+        cachep = kmem_cache_create_memcg(memcg, root_cache, memcg_name_buf);
         /*
          * If we could not create a memcg cache, do not complain, because
          * that's not critical at all as we can always proceed with the root
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 7e348cff814d..32175617cb75 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -264,13 +264,15 @@ EXPORT_SYMBOL(kmem_cache_create);
  * kmem_cache_create_memcg - Create a cache for a memory cgroup.
  * @memcg: The memory cgroup the new cache is for.
  * @root_cache: The parent of the new cache.
+ * @memcg_name: The name of the memory cgroup (used for naming the new cache).
  *
  * This function attempts to create a kmem cache that will serve allocation
  * requests going from @memcg to @root_cache. The new cache inherits properties
  * from its parent.
  */
 struct kmem_cache *kmem_cache_create_memcg(struct mem_cgroup *memcg,
-                                           struct kmem_cache *root_cache)
+                                           struct kmem_cache *root_cache,
+                                           const char *memcg_name)
 {
         struct kmem_cache *s = NULL;
         char *cache_name;
@@ -280,7 +282,8 @@ struct kmem_cache *kmem_cache_create_memcg(struct mem_cgroup *memcg,
 
         mutex_lock(&slab_mutex);
 
-        cache_name = memcg_create_cache_name(memcg, root_cache);
+        cache_name = kasprintf(GFP_KERNEL, "%s(%d:%s)", root_cache->name,
+                               memcg_cache_id(memcg), memcg_name);
         if (!cache_name)
                 goto out_unlock;