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Message-ID: <20140204145210.GH4890@dhcp22.suse.cz>
Date: Tue, 4 Feb 2014 15:52:10 +0100
From: Michal Hocko <mhocko@...e.cz>
To: Vladimir Davydov <vdavydov@...allels.com>
Cc: akpm@...ux-foundation.org, rientjes@...gle.com, penberg@...nel.org,
cl@...ux.com, glommer@...il.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, devel@...nvz.org
Subject: Re: [PATCH 3/8] memcg, slab: never try to merge memcg caches
On Sun 02-02-14 20:33:48, Vladimir Davydov wrote:
> Suppose we are creating memcg cache A that could be merged with cache B
> of the same memcg. Since any memcg cache has the same parameters as its
> parent cache, parent caches PA and PB of memcg caches A and B must be
> mergeable too. That means PA was merged with PB on creation or vice
> versa, i.e. PA = PB. From that it follows that A = B, and we couldn't
> even try to create cache B, because it already exists - a contradiction.
I cannot tell I understand the above but I am totally not sure about the
statement bellow.
> So let's remove unused code responsible for merging memcg caches.
How come the code was unused? find_mergeable called cache_match_memcg...
> Signed-off-by: Vladimir Davydov <vdavydov@...allels.com>
> ---
> mm/slab.h | 21 ++++-----------------
> mm/slab_common.c | 8 +++++---
> mm/slub.c | 19 +++++++++----------
> 3 files changed, 18 insertions(+), 30 deletions(-)
>
> diff --git a/mm/slab.h b/mm/slab.h
> index 8184a7cde272..3045316b7c9d 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -55,12 +55,12 @@ extern void create_boot_cache(struct kmem_cache *, const char *name,
> struct mem_cgroup;
> #ifdef CONFIG_SLUB
> struct kmem_cache *
> -__kmem_cache_alias(struct mem_cgroup *memcg, const char *name, size_t size,
> - size_t align, unsigned long flags, void (*ctor)(void *));
> +__kmem_cache_alias(const char *name, size_t size, size_t align,
> + unsigned long flags, void (*ctor)(void *));
> #else
> static inline struct kmem_cache *
> -__kmem_cache_alias(struct mem_cgroup *memcg, const char *name, size_t size,
> - size_t align, unsigned long flags, void (*ctor)(void *))
> +__kmem_cache_alias(const char *name, size_t size, size_t align,
> + unsigned long flags, void (*ctor)(void *))
> { return NULL; }
> #endif
>
> @@ -119,13 +119,6 @@ static inline bool is_root_cache(struct kmem_cache *s)
> return !s->memcg_params || s->memcg_params->is_root_cache;
> }
>
> -static inline bool cache_match_memcg(struct kmem_cache *cachep,
> - struct mem_cgroup *memcg)
> -{
> - return (is_root_cache(cachep) && !memcg) ||
> - (cachep->memcg_params->memcg == memcg);
> -}
> -
> static inline void memcg_bind_pages(struct kmem_cache *s, int order)
> {
> if (!is_root_cache(s))
> @@ -204,12 +197,6 @@ static inline bool is_root_cache(struct kmem_cache *s)
> return true;
> }
>
> -static inline bool cache_match_memcg(struct kmem_cache *cachep,
> - struct mem_cgroup *memcg)
> -{
> - return true;
> -}
> -
> static inline void memcg_bind_pages(struct kmem_cache *s, int order)
> {
> }
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 152d9b118b7a..a75834bb966d 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -200,9 +200,11 @@ kmem_cache_create_memcg(struct mem_cgroup *memcg, const char *name, size_t size,
> */
> flags &= CACHE_CREATE_MASK;
>
> - s = __kmem_cache_alias(memcg, name, size, align, flags, ctor);
> - if (s)
> - goto out_unlock;
> + if (!memcg) {
> + s = __kmem_cache_alias(name, size, align, flags, ctor);
> + if (s)
> + goto out_unlock;
> + }
>
> err = -ENOMEM;
> s = kmem_cache_zalloc(kmem_cache, GFP_KERNEL);
> diff --git a/mm/slub.c b/mm/slub.c
> index 2b1a6970e46f..962abfdfde06 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3686,9 +3686,8 @@ static int slab_unmergeable(struct kmem_cache *s)
> return 0;
> }
>
> -static struct kmem_cache *find_mergeable(struct mem_cgroup *memcg, size_t size,
> - size_t align, unsigned long flags, const char *name,
> - void (*ctor)(void *))
> +static struct kmem_cache *find_mergeable(size_t size, size_t align,
> + unsigned long flags, const char *name, void (*ctor)(void *))
> {
> struct kmem_cache *s;
>
> @@ -3707,11 +3706,14 @@ static struct kmem_cache *find_mergeable(struct mem_cgroup *memcg, size_t size,
> if (slab_unmergeable(s))
> continue;
>
> + if (!is_root_cache(s))
> + continue;
> +
> if (size > s->size)
> continue;
>
> if ((flags & SLUB_MERGE_SAME) != (s->flags & SLUB_MERGE_SAME))
> - continue;
> + continue;
> /*
> * Check if alignment is compatible.
> * Courtesy of Adrian Drzewiecki
> @@ -3722,21 +3724,18 @@ static struct kmem_cache *find_mergeable(struct mem_cgroup *memcg, size_t size,
> if (s->size - size >= sizeof(void *))
> continue;
>
> - if (!cache_match_memcg(s, memcg))
> - continue;
> -
> return s;
> }
> return NULL;
> }
>
> struct kmem_cache *
> -__kmem_cache_alias(struct mem_cgroup *memcg, const char *name, size_t size,
> - size_t align, unsigned long flags, void (*ctor)(void *))
> +__kmem_cache_alias(const char *name, size_t size, size_t align,
> + unsigned long flags, void (*ctor)(void *))
> {
> struct kmem_cache *s;
>
> - s = find_mergeable(memcg, size, align, flags, name, ctor);
> + s = find_mergeable(size, align, flags, name, ctor);
> if (s) {
> s->refcount++;
> /*
> --
> 1.7.10.4
>
--
Michal Hocko
SUSE Labs
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