[PATCH v6 02/10] mm: postpone kmem_cache memcg pointer initialization to memcg_link_cache()

[Roman Gushchin <guro@fb.com>]

Initialize kmem_cache->memcg_params.memcg pointer in
memcg_link_cache() rather than in init_memcg_params().

Once kmem_cache will hold a reference to the memory cgroup,
it will simplify the refcounting.

For non-root kmem_caches memcg_link_cache() is always called
before the kmem_cache becomes visible to a user, so it's safe.

Signed-off-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
---
 mm/slab.c        |  2 +-
 mm/slab.h        |  5 +++--
 mm/slab_common.c | 14 +++++++-------
 mm/slub.c        |  2 +-
 4 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index 9e3eee5568b6..a4091f8b3655 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1239,7 +1239,7 @@ void __init kmem_cache_init(void)
 				  nr_node_ids * sizeof(struct kmem_cache_node *),
 				  SLAB_HWCACHE_ALIGN, 0, 0);
 	list_add(&kmem_cache->list, &slab_caches);
-	memcg_link_cache(kmem_cache);
+	memcg_link_cache(kmem_cache, NULL);
 	slab_state = PARTIAL;
 
 	/*
diff --git a/mm/slab.h b/mm/slab.h
index 1176b61bb8fc..c16e5af0fb59 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -290,7 +290,7 @@ static __always_inline void memcg_uncharge_slab(struct page *page, int order,
 }
 
 extern void slab_init_memcg_params(struct kmem_cache *);
-extern void memcg_link_cache(struct kmem_cache *s);
+extern void memcg_link_cache(struct kmem_cache *s, struct mem_cgroup *memcg);
 extern void slab_deactivate_memcg_cache_rcu_sched(struct kmem_cache *s,
 				void (*deact_fn)(struct kmem_cache *));
 
@@ -345,7 +345,8 @@ static inline void slab_init_memcg_params(struct kmem_cache *s)
 {
 }
 
-static inline void memcg_link_cache(struct kmem_cache *s)
+static inline void memcg_link_cache(struct kmem_cache *s,
+				    struct mem_cgroup *memcg)
 {
 }
 
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 8092bdfc05d5..77df6029de8e 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -140,13 +140,12 @@ void slab_init_memcg_params(struct kmem_cache *s)
 }
 
 static int init_memcg_params(struct kmem_cache *s,
-		struct mem_cgroup *memcg, struct kmem_cache *root_cache)
+			     struct kmem_cache *root_cache)
 {
 	struct memcg_cache_array *arr;
 
 	if (root_cache) {
 		s->memcg_params.root_cache = root_cache;
-		s->memcg_params.memcg = memcg;
 		INIT_LIST_HEAD(&s->memcg_params.children_node);
 		INIT_LIST_HEAD(&s->memcg_params.kmem_caches_node);
 		return 0;
@@ -221,11 +220,12 @@ int memcg_update_all_caches(int num_memcgs)
 	return ret;
 }
 
-void memcg_link_cache(struct kmem_cache *s)
+void memcg_link_cache(struct kmem_cache *s, struct mem_cgroup *memcg)
 {
 	if (is_root_cache(s)) {
 		list_add(&s->root_caches_node, &slab_root_caches);
 	} else {
+		s->memcg_params.memcg = memcg;
 		list_add(&s->memcg_params.children_node,
 			 &s->memcg_params.root_cache->memcg_params.children);
 		list_add(&s->memcg_params.kmem_caches_node,
@@ -244,7 +244,7 @@ static void memcg_unlink_cache(struct kmem_cache *s)
 }
 #else
 static inline int init_memcg_params(struct kmem_cache *s,
-		struct mem_cgroup *memcg, struct kmem_cache *root_cache)
+				    struct kmem_cache *root_cache)
 {
 	return 0;
 }
@@ -384,7 +384,7 @@ static struct kmem_cache *create_cache(const char *name,
 	s->useroffset = useroffset;
 	s->usersize = usersize;
 
-	err = init_memcg_params(s, memcg, root_cache);
+	err = init_memcg_params(s, root_cache);
 	if (err)
 		goto out_free_cache;
 
@@ -394,7 +394,7 @@ static struct kmem_cache *create_cache(const char *name,
 
 	s->refcount = 1;
 	list_add(&s->list, &slab_caches);
-	memcg_link_cache(s);
+	memcg_link_cache(s, memcg);
 out:
 	if (err)
 		return ERR_PTR(err);
@@ -998,7 +998,7 @@ struct kmem_cache *__init create_kmalloc_cache(const char *name,
 
 	create_boot_cache(s, name, size, flags, useroffset, usersize);
 	list_add(&s->list, &slab_caches);
-	memcg_link_cache(s);
+	memcg_link_cache(s, NULL);
 	s->refcount = 1;
 	return s;
 }
diff --git a/mm/slub.c b/mm/slub.c
index 1802c87799ff..9cb2eef62a37 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4213,7 +4213,7 @@ static struct kmem_cache * __init bootstrap(struct kmem_cache *static_cache)
 	}
 	slab_init_memcg_params(s);
 	list_add(&s->list, &slab_caches);
-	memcg_link_cache(s);
+	memcg_link_cache(s, NULL);
 	return s;
 }
 
-- 
2.20.1