From f315e3fa1cf5b3317fc948708645fff889ce1e63 Mon Sep 17 00:00:00 2001 From: Joonsoo Kim Date: Mon, 2 Dec 2013 17:49:41 +0900 Subject: slab: restrict the number of objects in a slab To prepare to implement byte sized index for managing the freelist of a slab, we should restrict the number of objects in a slab to be less or equal to 256, since byte only represent 256 different values. Setting the size of object to value equal or more than newly introduced SLAB_OBJ_MIN_SIZE ensures that the number of objects in a slab is less or equal to 256 for a slab with 1 page. If page size is rather larger than 4096, above assumption would be wrong. In this case, we would fall back on 2 bytes sized index. If minimum size of kmalloc is less than 16, we use it as minimum object size and give up this optimization. Signed-off-by: Joonsoo Kim Signed-off-by: Pekka Enberg --- include/linux/slab.h | 11 +++++++++++ 1 file changed, 11 insertions(+) (limited to 'include/linux/slab.h') diff --git a/include/linux/slab.h b/include/linux/slab.h index 9260abdd67df..d015dec02bf3 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -201,6 +201,17 @@ struct kmem_cache { #ifndef KMALLOC_SHIFT_LOW #define KMALLOC_SHIFT_LOW 5 #endif + +/* + * This restriction comes from byte sized index implementation. + * Page size is normally 2^12 bytes and, in this case, if we want to use + * byte sized index which can represent 2^8 entries, the size of the object + * should be equal or greater to 2^12 / 2^8 = 2^4 = 16. + * If minimum size of kmalloc is less than 16, we use it as minimum object + * size and give up to use byte sized index. + */ +#define SLAB_OBJ_MIN_SIZE (KMALLOC_SHIFT_LOW < 4 ? \ + (1 << KMALLOC_SHIFT_LOW) : 16) #endif #ifdef CONFIG_SLUB -- cgit v1.2.3-58-ga151