From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f71.google.com (mail-wm0-f71.google.com [74.125.82.71]) by kanga.kvack.org (Postfix) with ESMTP id C04A46B0006 for ; Mon, 5 Mar 2018 15:07:53 -0500 (EST) Received: by mail-wm0-f71.google.com with SMTP id u83so5107149wmb.3 for ; Mon, 05 Mar 2018 12:07:53 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id j185sor2200502wma.11.2018.03.05.12.07.52 for (Google Transport Security); Mon, 05 Mar 2018 12:07:52 -0800 (PST) From: Alexey Dobriyan Subject: [PATCH 02/25] slab: make kmalloc_index() return "unsigned int" Date: Mon, 5 Mar 2018 23:07:07 +0300 Message-Id: <20180305200730.15812-2-adobriyan@gmail.com> In-Reply-To: <20180305200730.15812-1-adobriyan@gmail.com> References: <20180305200730.15812-1-adobriyan@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: akpm@linux-foundation.org Cc: cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, linux-mm@kvack.org, adobriyan@gmail.com 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. Signed-off-by: Alexey Dobriyan --- include/linux/slab.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/include/linux/slab.h b/include/linux/slab.h index 231abc8976c5..296f33a512eb 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; -- 2.16.1 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org