From: Alexey Dobriyan Date: Thu, 5 Apr 2018 23:20:22 +0000 (-0700) Subject: slab: make kmalloc_index() return "unsigned int" X-Git-Tag: v4.19~1277^2~83 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=36071a279b4100afe9fbee18727ad78daa307591;p=platform%2Fkernel%2Flinux-rpi3.git slab: make kmalloc_index() return "unsigned int" kmalloc_index() return index into an array of kmalloc kmem caches, therefore should be unsigned. Space savings with SLUB on trimmed down .config: add/remove: 0/1 grow/shrink: 6/56 up/down: 85/-557 (-472) Function old new delta calculate_sizes 924 983 +59 on_freelist 589 604 +15 init_cache_random_seq 122 127 +5 ext4_mb_init 1206 1210 +4 slab_pad_check.part 270 271 +1 cpu_partial_store 112 113 +1 usersize_show 28 27 -1 ... new_slab 1871 1837 -34 slab_order 204 - -204 This patch start a series of converting SLUB (mostly) to "unsigned int". 1) Most integers in the code are in fact unsigned entities: array indexes, lengths, buffer sizes, allocation orders. It is therefore better to use unsigned variables 2) Some integers in the code are either "size_t" or "unsigned long" for no reason. size_t usually comes from people trying to maintain type correctness and figuring out that "sizeof" operator returns size_t or memset/memcpy takes size_t so should everything passed to it. However the number of 4GB+ objects in the kernel is very small. Most, if not all, dynamically allocated objects with kmalloc() or kmem_cache_create() aren't actually big. Maintaining wide types doesn't do anything. 64-bit ops are bigger than 32-bit on our beloved x86_64, so try to not use 64-bit where it isn't necessary (read: everywhere where integers are integers not pointers) 3) in case of SLAB allocators, there are additional limitations *) page->inuse, page->objects are only 16-/15-bit, *) cache size was always 32-bit *) slab orders are small, order 20 is needed to go 64-bit on x86_64 (PAGE_SIZE << order) Basically everything is 32-bit except kmalloc(1ULL<<32) which gets shortcut through page allocator. Christoph said: : : That changes with large base page size on power and ARM64 f.e. but then : we do not want to encourage larger allocations through slab anyways. Link: http://lkml.kernel.org/r/20180305200730.15812-2-adobriyan@gmail.com Signed-off-by: Alexey Dobriyan Acked-by: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/include/linux/slab.h b/include/linux/slab.h index 231abc8..296f33a 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -308,7 +308,7 @@ extern struct kmem_cache *kmalloc_dma_caches[KMALLOC_SHIFT_HIGH + 1]; * 2 = 129 .. 192 bytes * n = 2^(n-1)+1 .. 2^n */ -static __always_inline int kmalloc_index(size_t size) +static __always_inline unsigned int kmalloc_index(size_t size) { if (!size) return 0; @@ -504,7 +504,7 @@ static __always_inline void *kmalloc(size_t size, gfp_t flags) return kmalloc_large(size, flags); #ifndef CONFIG_SLOB if (!(flags & GFP_DMA)) { - int index = kmalloc_index(size); + unsigned int index = kmalloc_index(size); if (!index) return ZERO_SIZE_PTR; @@ -542,7 +542,7 @@ static __always_inline void *kmalloc_node(size_t size, gfp_t flags, int node) #ifndef CONFIG_SLOB if (__builtin_constant_p(size) && size <= KMALLOC_MAX_CACHE_SIZE && !(flags & GFP_DMA)) { - int i = kmalloc_index(size); + unsigned int i = kmalloc_index(size); if (!i) return ZERO_SIZE_PTR;