From 94a58c360a45c066ab5472cfd2bf2a4ba63aa532 Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Fri, 20 Nov 2015 15:56:48 -0800 Subject: slab.h: sprinkle __assume_aligned attributes The various allocators return aligned memory. Telling the compiler that allows it to generate better code in many cases, for example when the return value is immediately passed to memset(). Some code does become larger, but at least we win twice as much as we lose: $ scripts/bloat-o-meter /tmp/vmlinux vmlinux add/remove: 0/0 grow/shrink: 13/52 up/down: 995/-2140 (-1145) An example of the different (and smaller) code can be seen in mm_alloc(). Before: : 48 8d 78 08 lea 0x8(%rax),%rdi : 48 89 c1 mov %rax,%rcx : 48 89 c2 mov %rax,%rdx : 48 c7 00 00 00 00 00 movq $0x0,(%rax) : 48 c7 80 48 03 00 00 movq $0x0,0x348(%rax) : 00 00 00 00 : 31 c0 xor %eax,%eax : 48 83 e7 f8 and $0xfffffffffffffff8,%rdi : 48 29 f9 sub %rdi,%rcx : 81 c1 50 03 00 00 add $0x350,%ecx : c1 e9 03 shr $0x3,%ecx : f3 48 ab rep stos %rax,%es:(%rdi) After: : 48 89 c2 mov %rax,%rdx : b9 6a 00 00 00 mov $0x6a,%ecx : 31 c0 xor %eax,%eax : 48 89 d7 mov %rdx,%rdi : f3 48 ab rep stos %rax,%es:(%rdi) So gcc's strategy is to do two possibly (but not really, of course) unaligned stores to the first and last word, then do an aligned rep stos covering the middle part with a little overlap. Maybe arches which do not allow unaligned stores gain even more. I don't know if gcc can actually make use of alignments greater than 8 for anything, so one could probably drop the __assume_xyz_alignment macros and just use __assume_aligned(8). The increases in code size are mostly caused by gcc deciding to opencode strlen() using the check-four-bytes-at-a-time trick when it knows the buffer is sufficiently aligned (one function grew by 200 bytes). Now it turns out that many of these strlen() calls showing up were in fact redundant, and they're gone from -next. Applying the two patches to next-20151001 bloat-o-meter instead says add/remove: 0/0 grow/shrink: 6/52 up/down: 244/-2140 (-1896) Signed-off-by: Rasmus Villemoes Acked-by: Christoph Lameter Cc: David Rientjes Cc: Pekka Enberg Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/slab.h | 43 ++++++++++++++++++++++++++----------------- 1 file changed, 26 insertions(+), 17 deletions(-) (limited to 'include/linux/slab.h') diff --git a/include/linux/slab.h b/include/linux/slab.h index 7c82e3b..9694077 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -158,6 +158,24 @@ size_t ksize(const void *); #endif /* + * Setting ARCH_SLAB_MINALIGN in arch headers allows a different alignment. + * Intended for arches that get misalignment faults even for 64 bit integer + * aligned buffers. + */ +#ifndef ARCH_SLAB_MINALIGN +#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long) +#endif + +/* + * kmalloc and friends return ARCH_KMALLOC_MINALIGN aligned + * pointers. kmem_cache_alloc and friends return ARCH_SLAB_MINALIGN + * aligned pointers. + */ +#define __assume_kmalloc_alignment __assume_aligned(ARCH_KMALLOC_MINALIGN) +#define __assume_slab_alignment __assume_aligned(ARCH_SLAB_MINALIGN) +#define __assume_page_alignment __assume_aligned(PAGE_SIZE) + +/* * Kmalloc array related definitions */ @@ -286,8 +304,8 @@ static __always_inline int kmalloc_index(size_t size) } #endif /* !CONFIG_SLOB */ -void *__kmalloc(size_t size, gfp_t flags); -void *kmem_cache_alloc(struct kmem_cache *, gfp_t flags); +void *__kmalloc(size_t size, gfp_t flags) __assume_kmalloc_alignment; +void *kmem_cache_alloc(struct kmem_cache *, gfp_t flags) __assume_slab_alignment; void kmem_cache_free(struct kmem_cache *, void *); /* @@ -301,8 +319,8 @@ void kmem_cache_free_bulk(struct kmem_cache *, size_t, void **); bool kmem_cache_alloc_bulk(struct kmem_cache *, gfp_t, size_t, void **); #ifdef CONFIG_NUMA -void *__kmalloc_node(size_t size, gfp_t flags, int node); -void *kmem_cache_alloc_node(struct kmem_cache *, gfp_t flags, int node); +void *__kmalloc_node(size_t size, gfp_t flags, int node) __assume_kmalloc_alignment; +void *kmem_cache_alloc_node(struct kmem_cache *, gfp_t flags, int node) __assume_slab_alignment; #else static __always_inline void *__kmalloc_node(size_t size, gfp_t flags, int node) { @@ -316,12 +334,12 @@ static __always_inline void *kmem_cache_alloc_node(struct kmem_cache *s, gfp_t f #endif #ifdef CONFIG_TRACING -extern void *kmem_cache_alloc_trace(struct kmem_cache *, gfp_t, size_t); +extern void *kmem_cache_alloc_trace(struct kmem_cache *, gfp_t, size_t) __assume_slab_alignment; #ifdef CONFIG_NUMA extern void *kmem_cache_alloc_node_trace(struct kmem_cache *s, gfp_t gfpflags, - int node, size_t size); + int node, size_t size) __assume_slab_alignment; #else static __always_inline void * kmem_cache_alloc_node_trace(struct kmem_cache *s, @@ -354,10 +372,10 @@ kmem_cache_alloc_node_trace(struct kmem_cache *s, } #endif /* CONFIG_TRACING */ -extern void *kmalloc_order(size_t size, gfp_t flags, unsigned int order); +extern void *kmalloc_order(size_t size, gfp_t flags, unsigned int order) __assume_page_alignment; #ifdef CONFIG_TRACING -extern void *kmalloc_order_trace(size_t size, gfp_t flags, unsigned int order); +extern void *kmalloc_order_trace(size_t size, gfp_t flags, unsigned int order) __assume_page_alignment; #else static __always_inline void * kmalloc_order_trace(size_t size, gfp_t flags, unsigned int order) @@ -482,15 +500,6 @@ static __always_inline void *kmalloc_node(size_t size, gfp_t flags, int node) return __kmalloc_node(size, flags, node); } -/* - * Setting ARCH_SLAB_MINALIGN in arch headers allows a different alignment. - * Intended for arches that get misalignment faults even for 64 bit integer - * aligned buffers. - */ -#ifndef ARCH_SLAB_MINALIGN -#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long) -#endif - struct memcg_cache_array { struct rcu_head rcu; struct kmem_cache *entries[0]; -- cgit v1.1 From 865762a8119e74b5f0e236d2d8eaaf8be9292a06 Mon Sep 17 00:00:00 2001 From: Jesper Dangaard Brouer Date: Fri, 20 Nov 2015 15:57:58 -0800 Subject: slab/slub: adjust kmem_cache_alloc_bulk API Adjust kmem_cache_alloc_bulk API before we have any real users. Adjust API to return type 'int' instead of previously type 'bool'. This is done to allow future extension of the bulk alloc API. A future extension could be to allow SLUB to stop at a page boundary, when specified by a flag, and then return the number of objects. The advantage of this approach, would make it easier to make bulk alloc run without local IRQs disabled. With an approach of cmpxchg "stealing" the entire c->freelist or page->freelist. To avoid overshooting we would stop processing at a slab-page boundary. Else we always end up returning some objects at the cost of another cmpxchg. To keep compatible with future users of this API linking against an older kernel when using the new flag, we need to return the number of allocated objects with this API change. Signed-off-by: Jesper Dangaard Brouer Cc: Vladimir Davydov Acked-by: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/slab.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include/linux/slab.h') diff --git a/include/linux/slab.h b/include/linux/slab.h index 9694077..2037a86 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -316,7 +316,7 @@ void kmem_cache_free(struct kmem_cache *, void *); * Note that interrupts must be enabled when calling these functions. */ void kmem_cache_free_bulk(struct kmem_cache *, size_t, void **); -bool kmem_cache_alloc_bulk(struct kmem_cache *, gfp_t, size_t, void **); +int kmem_cache_alloc_bulk(struct kmem_cache *, gfp_t, size_t, void **); #ifdef CONFIG_NUMA void *__kmalloc_node(size_t size, gfp_t flags, int node) __assume_kmalloc_alignment; -- cgit v1.1