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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