[Devel] [PATCH] memcg, slab: cleanup memcg cache creation

[Vladimir Davydov]

This patch cleanups 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 at parallels.com>
---
 include/linux/memcontrol.h |    9 +++++
 mm/memcontrol.c            |   89 ++++++++++++++++++++------------------------
 mm/slab_common.c           |    5 ++-
 3 files changed, 54 insertions(+), 49 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index abd0113b6620..84e4801fc36c 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -497,6 +497,9 @@ void __memcg_kmem_commit_charge(struct page *page,
 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);
@@ -641,6 +644,12 @@ static inline int memcg_cache_id(struct mem_cgroup *memcg)
 	return -1;
 }
 
+static inline char *memcg_create_cache_name(struct mem_cgroup *memcg,
+					    struct kmem_cache *root_cache)
+{
+	return NULL;
+}
+
 static inline int memcg_alloc_cache_params(struct mem_cgroup *memcg,
 		struct kmem_cache *s, struct kmem_cache *root_cache)
 {
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 53385cd4e6f0..43e08b7bb365 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3193,6 +3193,32 @@ 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(PATH_MAX, GFP_KERNEL);
+		if (!buf)
+			return NULL;
+	}
+
+	rcu_read_lock();
+	snprintf(buf, PATH_MAX, "%s(%d:%s)", root_cache->name,
+		 memcg_cache_id(memcg), cgroup_name(memcg->css.cgroup));
+	rcu_read_unlock();
+
+	return kstrdup(buf, GFP_KERNEL);
+}
+
 int memcg_alloc_cache_params(struct mem_cgroup *memcg, struct kmem_cache *s,
 			     struct kmem_cache *root_cache)
 {
@@ -3397,44 +3423,6 @@ 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_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_name) {
-		tmp_name = kmalloc(PATH_MAX, GFP_KERNEL);
-		if (!tmp_name)
-			goto out;
-	}
-
-	rcu_read_lock();
-	snprintf(tmp_name, PATH_MAX, "%s(%d:%s)", s->name,
-			 memcg_cache_id(memcg), cgroup_name(memcg->css.cgroup));
-	rcu_read_unlock();
-
-	new = kmem_cache_create_memcg(memcg, tmp_name, 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;
@@ -3481,12 +3469,6 @@ 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;
@@ -3504,13 +3486,24 @@ 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 *s = 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, s->name, s->object_size, s->align,
+				      (s->flags & ~SLAB_PANIC), s->ctor, s);
+	if (new)
+		new->allocflags |= __GFP_KMEMCG;
+	css_put(&memcg->css);
 	kfree(cw);
 }
 
diff --git a/mm/slab_common.c b/mm/slab_common.c
index e77b51eb7347..11857abf7057 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -215,7 +215,10 @@ kmem_cache_create_memcg(struct mem_cgroup *memcg, const char *name, size_t size,
 	s->align = calculate_alignment(flags, align, size);
 	s->ctor = ctor;
 
-	s->name = kstrdup(name, GFP_KERNEL);
+	if (memcg)
+		s->name = memcg_create_cache_name(memcg, parent_cache);
+	else
+		s->name = kstrdup(name, GFP_KERNEL);
 	if (!s->name)
 		goto out_free_cache;
 
-- 
1.7.10.4