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Date:   Fri, 10 May 2019 17:32:29 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Roman Gushchin <guro@...com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kernel Team <kernel-team@...com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        Christoph Lameter <cl@...ux.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Cgroups <cgroups@...r.kernel.org>
Subject: Re: [PATCH v3 1/7] mm: postpone kmem_cache memcg pointer
 initialization to memcg_link_cache()

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

Reviewed-by: Shakeel Butt <shakeelb@...gle.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
>

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