diff options
| -rw-r--r-- | arch/x86/Kconfig | 4 | ||||
| -rw-r--r-- | mm/slub.c | 93 |
2 files changed, 92 insertions, 5 deletions
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index c95482b6b6d..9d0acedf5f3 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -52,6 +52,10 @@ config HAVE_LATENCYTOP_SUPPORT config SEMAPHORE_SLEEPERS def_bool y +config FAST_CMPXCHG_LOCAL + bool + default y + config MMU def_bool y diff --git a/mm/slub.c b/mm/slub.c index 5995626e0cf..20ab8f0a4eb 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -149,6 +149,13 @@ static inline void ClearSlabDebug(struct page *page) /* Enable to test recovery from slab corruption on boot */ #undef SLUB_RESILIENCY_TEST +/* + * Currently fastpath is not supported if preemption is enabled. + */ +#if defined(CONFIG_FAST_CMPXCHG_LOCAL) && !defined(CONFIG_PREEMPT) +#define SLUB_FASTPATH +#endif + #if PAGE_SHIFT <= 12 /* @@ -1493,7 +1500,11 @@ static void *__slab_alloc(struct kmem_cache *s, { void **object; struct page *new; +#ifdef SLUB_FASTPATH + unsigned long flags; + local_irq_save(flags); +#endif if (!c->page) goto new_slab; @@ -1512,7 +1523,12 @@ load_freelist: c->page->inuse = s->objects; c->page->freelist = c->page->end; c->node = page_to_nid(c->page); +unlock_out: slab_unlock(c->page); +out: +#ifdef SLUB_FASTPATH + local_irq_restore(flags); +#endif return object; another_slab: @@ -1542,7 +1558,8 @@ new_slab: c->page = new; goto load_freelist; } - return NULL; + object = NULL; + goto out; debug: object = c->page->freelist; if (!alloc_debug_processing(s, c->page, object, addr)) @@ -1551,8 +1568,7 @@ debug: c->page->inuse++; c->page->freelist = object[c->offset]; c->node = -1; - slab_unlock(c->page); - return object; + goto unlock_out; } /* @@ -1569,9 +1585,36 @@ static __always_inline void *slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node, void *addr) { void **object; - unsigned long flags; struct kmem_cache_cpu *c; +/* + * The SLUB_FASTPATH path is provisional and is currently disabled if the + * kernel is compiled with preemption or if the arch does not support + * fast cmpxchg operations. There are a couple of coming changes that will + * simplify matters and allow preemption. Ultimately we may end up making + * SLUB_FASTPATH the default. + * + * 1. The introduction of the per cpu allocator will avoid array lookups + * through get_cpu_slab(). A special register can be used instead. + * + * 2. The introduction of per cpu atomic operations (cpu_ops) means that + * we can realize the logic here entirely with per cpu atomics. The + * per cpu atomic ops will take care of the preemption issues. + */ + +#ifdef SLUB_FASTPATH + c = get_cpu_slab(s, raw_smp_processor_id()); + do { + object = c->freelist; + if (unlikely(is_end(object) || !node_match(c, node))) { + object = __slab_alloc(s, gfpflags, node, addr, c); + break; + } + } while (cmpxchg_local(&c->freelist, object, object[c->offset]) + != object); +#else + unsigned long flags; + local_irq_save(flags); c = get_cpu_slab(s, smp_processor_id()); if (unlikely(is_end(c->freelist) || !node_match(c, node))) @@ -1583,6 +1626,7 @@ static __always_inline void *slab_alloc(struct kmem_cache *s, c->freelist = object[c->offset]; } local_irq_restore(flags); +#endif if (unlikely((gfpflags & __GFP_ZERO) && object)) memset(object, 0, c->objsize); @@ -1618,6 +1662,11 @@ static void __slab_free(struct kmem_cache *s, struct page *page, void *prior; void **object = (void *)x; +#ifdef SLUB_FASTPATH + unsigned long flags; + + local_irq_save(flags); +#endif slab_lock(page); if (unlikely(SlabDebug(page))) @@ -1643,6 +1692,9 @@ checks_ok: out_unlock: slab_unlock(page); +#ifdef SLUB_FASTPATH + local_irq_restore(flags); +#endif return; slab_empty: @@ -1653,6 +1705,9 @@ slab_empty: remove_partial(s, page); slab_unlock(page); +#ifdef SLUB_FASTPATH + local_irq_restore(flags); +#endif discard_slab(s, page); return; @@ -1677,9 +1732,36 @@ static __always_inline void slab_free(struct kmem_cache *s, struct page *page, void *x, void *addr) { void **object = (void *)x; - unsigned long flags; struct kmem_cache_cpu *c; +#ifdef SLUB_FASTPATH + void **freelist; + + c = get_cpu_slab(s, raw_smp_processor_id()); + debug_check_no_locks_freed(object, s->objsize); + do { + freelist = c->freelist; + barrier(); + /* + * If the compiler would reorder the retrieval of c->page to + * come before c->freelist then an interrupt could + * change the cpu slab before we retrieve c->freelist. We + * could be matching on a page no longer active and put the + * object onto the freelist of the wrong slab. + * + * On the other hand: If we already have the freelist pointer + * then any change of cpu_slab will cause the cmpxchg to fail + * since the freelist pointers are unique per slab. + */ + if (unlikely(page != c->page || c->node < 0)) { + __slab_free(s, page, x, addr, c->offset); + break; + } + object[c->offset] = freelist; + } while (cmpxchg_local(&c->freelist, freelist, object) != freelist); +#else + unsigned long flags; + local_irq_save(flags); debug_check_no_locks_freed(object, s->objsize); c = get_cpu_slab(s, smp_processor_id()); @@ -1690,6 +1772,7 @@ static __always_inline void slab_free(struct kmem_cache *s, __slab_free(s, page, x, addr, c->offset); local_irq_restore(flags); +#endif } void kmem_cache_free(struct kmem_cache *s, void *x) |