[PATCH v2 2/3] mm/slab: support slab merge

[Joonsoo Kim]

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.

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
functions.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
---
 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 *));
-#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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