Re: [PATCH v3 1/7] mm: postpone kmem_cache memcg pointer initialization to memcg_link_cache()

Shakeel Butt
2019-05-11T00:32:43Z

Date: Wed, May 8, 2019 at 1:30 PM
To: Andrew Morton, Shakeel Butt
Cc: <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>,
<kernel-team@fb.com>, Johannes Weiner, Michal Hocko, Rik van Riel,
Christoph Lameter, Vladimir Davydov, <cgroups@vger.kernel.org>, 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 <guro@fb.com>

Reviewed-by: Shakeel Butt <shakeelb@google.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 2915d912e89a..f6eff59e018e 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 5b2e364102e1..16f7e4f5a141 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -4219,7 +4219,7 @@ 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
>