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 --- mm/slab.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) (limited to 'mm') diff --git a/mm/slab.c b/mm/slab.c index 878354b26b72..9d4c7b50dfdc 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -157,6 +157,17 @@ #define ARCH_KMALLOC_FLAGS SLAB_HWCACHE_ALIGN #endif +#define FREELIST_BYTE_INDEX (((PAGE_SIZE >> BITS_PER_BYTE) \ + <= SLAB_OBJ_MIN_SIZE) ? 1 : 0) + +#if FREELIST_BYTE_INDEX +typedef unsigned char freelist_idx_t; +#else +typedef unsigned short freelist_idx_t; +#endif + +#define SLAB_OBJ_MAX_NUM (1 << sizeof(freelist_idx_t) * BITS_PER_BYTE) + /* * true if a page was allocated from pfmemalloc reserves for network-based * swap @@ -2016,6 +2027,10 @@ static size_t calculate_slab_order(struct kmem_cache *cachep, if (!num) continue; + /* Can't handle number of objects more than SLAB_OBJ_MAX_NUM */ + if (num > SLAB_OBJ_MAX_NUM) + break; + if (flags & CFLGS_OFF_SLAB) { /* * Max number of objs-per-slab for caches which @@ -2258,6 +2273,12 @@ __kmem_cache_create (struct kmem_cache *cachep, unsigned long flags) flags |= CFLGS_OFF_SLAB; size = ALIGN(size, cachep->align); + /* + * We should restrict the number of objects in a slab to implement + * byte sized index. Refer comment on SLAB_OBJ_MIN_SIZE definition. + */ + if (FREELIST_BYTE_INDEX && size < SLAB_OBJ_MIN_SIZE) + size = ALIGN(SLAB_OBJ_MIN_SIZE, cachep->align); left_over = calculate_slab_order(cachep, size, cachep->align, flags); -- cgit v1.2.3