linux-kernel - [PATCH 3/3] mm/slab: support slab merge

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Date:	Thu, 21 Aug 2014 17:11:15 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: [PATCH 3/3] 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

<Before>
Slab: 25136 kB

<After>
Slab: 24364 kB

We can save 3% memory used by slab.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
---
 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 09b060e..a1cc1c9 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2052,6 +2052,26 @@ 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 7c6e1ed..13845d0 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -89,7 +89,7 @@ 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 *));
-#ifdef CONFIG_SLUB
+#ifndef CONFIG_SLOB
 struct kmem_cache *
 __kmem_cache_alias(const char *name, size_t size, size_t align,
 		   unsigned long flags, void (*ctor)(void *));
-- 
1.7.9.5

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