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Date:	Mon, 15 Sep 2014 15:25:56 +0900
From:	Joonsoo Kim <>
To:	Andrew Morton <>
Cc:	Christoph Lameter <>,
	Pekka Enberg <>,
	David Rientjes <>,,, Joonsoo Kim <>
Subject: [PATCH v2 2/3] mm/slab: support slab merge

Slab merge is good feature to reduce fragmentation. If new creating slab
have similar size and property with exsitent slab, this feature reuse
it rather than creating new one. As a result, objects are packed into
fewer slabs so that fragmentation is reduced.

Below is result of my testing.

* After boot, sleep 20; cat /proc/meminfo | grep Slab

Slab: 25136 kB

Slab: 24364 kB

We can save 3% memory used by slab.

For supporting this feature in SLAB, we need to implement SLAB specific
kmem_cache_flag() and __kmem_cache_alias(), because SLUB implements
some SLUB specific processing related to debug flag and object size
change on these functions.

v2: add commit description for the reason to implement SLAB specific

Signed-off-by: Joonsoo Kim <>
 mm/slab.c |   20 ++++++++++++++++++++
 mm/slab.h |    2 +-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/mm/slab.c b/mm/slab.c
index 5927a17..cc246f2 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2104,6 +2104,26 @@ static int __init_refok setup_cpu_cache(struct kmem_cache *cachep, gfp_t gfp)
 	return 0;
+unsigned long kmem_cache_flags(unsigned long object_size,
+	unsigned long flags, const char *name,
+	void (*ctor)(void *))
+	return flags;
+struct kmem_cache *
+__kmem_cache_alias(const char *name, size_t size, size_t align,
+		   unsigned long flags, void (*ctor)(void *))
+	struct kmem_cache *cachep;
+	cachep = find_mergeable(size, align, flags, name, ctor);
+	if (cachep)
+		cachep->refcount++;
+	return cachep;
  * __kmem_cache_create - Create a cache.
  * @cachep: cache management descriptor
diff --git a/mm/slab.h b/mm/slab.h
index 857758b..46c7c25 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -90,7 +90,7 @@ struct mem_cgroup;
 int slab_unmergeable(struct kmem_cache *s);
 struct kmem_cache *find_mergeable(size_t size, size_t align,
 		unsigned long flags, const char *name, void (*ctor)(void *));
+#ifndef CONFIG_SLOB
 struct kmem_cache *
 __kmem_cache_alias(const char *name, size_t size, size_t align,
 		   unsigned long flags, void (*ctor)(void *));

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