Commit a44cb944 authored by Vladimir Davydov's avatar Vladimir Davydov Committed by Linus Torvalds
Browse files

memcg, slab: never try to merge memcg caches 



When a kmem cache is created (kmem_cache_create_memcg()), we first try to
find a compatible cache that already exists and can handle requests from
the new cache, i.e.  has the same object size, alignment, ctor, etc.  If
there is such a cache, we do not create any new caches, instead we simply
increment the refcount of the cache found and return it.

Currently we do this procedure not only when creating root caches, but
also for memcg caches.  However, there is no point in that, because, as
every memcg cache has exactly the same parameters as its parent and cache
merging cannot be turned off in runtime (only on boot by passing
"slub_nomerge"), the root caches of any two potentially mergeable memcg
caches should be merged already, i.e.  it must be the same root cache, and
therefore we couldn't even get to the memcg cache creation, because it
already exists.

The only exception is boot caches - they are explicitly forbidden to be
merged by setting their refcount to -1.  There are currently only two of
them - kmem_cache and kmem_cache_node, which are used in slab internals (I
do not count kmalloc caches as their refcount is set to 1 immediately
after creation).  Since they are prevented from merging preliminary I
guess we should avoid to merge their children too.

So let's remove the useless code responsible for merging memcg caches.

Signed-off-by: default avatarVladimir Davydov <vdavydov@parallels.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Glauber Costa <glommer@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent cf7bc58f

mm/slab.h

+4 −17
Original line number Diff line number Diff line
@@ -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)

{

}

mm/slab_common.c

+5 −3
Original line number Diff line number Diff line
@@ -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 (!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);

mm/slub.c

+9 −10
Original line number Diff line number Diff line
@@ -3685,6 +3685,9 @@ static int slab_unmergeable(struct kmem_cache *s) 
	if (slub_nomerge || (s->flags & SLUB_NEVER_MERGE))

		return 1;



	if (!is_root_cache(s))

		return 1;



	if (s->ctor)

		return 1;
@@ -3697,9 +3700,8 @@ 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;
@@ -3733,21 +3735,18 @@ 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++;

		/*

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