[PATCH v2 1/6] mm: postpone kmem_cache memcg pointer initialization to memcg_link_cache()

[Roman Gushchin]

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 <g...@fb.com>
---
 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 b1eefe751d2a..57a332f524cf 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1268,7 +1268,7 @@ 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 43ac818b8592..6a562ca72bca 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -289,7 +289,7 @@ 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 *));
 
@@ -344,7 +344,8 @@ 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 58251ba63e4a..6e00bdf8618d 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);
@@ -997,7 +997,7 @@ 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 a34fbe1f6ede..2b9244529d76 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4224,7 +4224,7 @@ 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