diff options
Diffstat (limited to 'mm/slub.c')
| -rw-r--r-- | mm/slub.c | 129 |
1 files changed, 52 insertions, 77 deletions
@@ -2,10 +2,11 @@ * SLUB: A slab allocator that limits cache line use instead of queuing * objects in per cpu and per node lists. * - * The allocator synchronizes using per slab locks and only - * uses a centralized lock to manage a pool of partial slabs. + * The allocator synchronizes using per slab locks or atomic operatios + * and only uses a centralized lock to manage a pool of partial slabs. * * (C) 2007 SGI, Christoph Lameter + * (C) 2011 Linux Foundation, Christoph Lameter */ #include <linux/mm.h> @@ -32,15 +33,27 @@ /* * Lock order: - * 1. slab_lock(page) - * 2. slab->list_lock + * 1. slub_lock (Global Semaphore) + * 2. node->list_lock + * 3. slab_lock(page) (Only on some arches and for debugging) * - * The slab_lock protects operations on the object of a particular - * slab and its metadata in the page struct. If the slab lock - * has been taken then no allocations nor frees can be performed - * on the objects in the slab nor can the slab be added or removed - * from the partial or full lists since this would mean modifying - * the page_struct of the slab. + * slub_lock + * + * The role of the slub_lock is to protect the list of all the slabs + * and to synchronize major metadata changes to slab cache structures. + * + * The slab_lock is only used for debugging and on arches that do not + * have the ability to do a cmpxchg_double. It only protects the second + * double word in the page struct. Meaning + * A. page->freelist -> List of object free in a page + * B. page->counters -> Counters of objects + * C. page->frozen -> frozen state + * + * If a slab is frozen then it is exempt from list management. It is not + * on any list. The processor that froze the slab is the one who can + * perform list operations on the page. Other processors may put objects + * onto the freelist but the processor that froze the slab is the only + * one that can retrieve the objects from the page's freelist. * * The list_lock protects the partial and full list on each node and * the partial slab counter. If taken then no new slabs may be added or @@ -53,20 +66,6 @@ * slabs, operations can continue without any centralized lock. F.e. * allocating a long series of objects that fill up slabs does not require * the list lock. - * - * The lock order is sometimes inverted when we are trying to get a slab - * off a list. We take the list_lock and then look for a page on the list - * to use. While we do that objects in the slabs may be freed. We can - * only operate on the slab if we have also taken the slab_lock. So we use - * a slab_trylock() on the slab. If trylock was successful then no frees - * can occur anymore and we can use the slab for allocations etc. If the - * slab_trylock() does not succeed then frees are in progress in the slab and - * we must stay away from it for a while since we may cause a bouncing - * cacheline if we try to acquire the lock. So go onto the next slab. - * If all pages are busy then we may allocate a new slab instead of reusing - * a partial slab. A new slab has no one operating on it and thus there is - * no danger of cacheline contention. - * * Interrupts are disabled during allocation and deallocation in order to * make the slab allocator safe to use in the context of an irq. In addition * interrupts are disabled to ensure that the processor does not change @@ -342,6 +341,19 @@ static inline int oo_objects(struct kmem_cache_order_objects x) return x.x & OO_MASK; } +/* + * Per slab locking using the pagelock + */ +static __always_inline void slab_lock(struct page *page) +{ + bit_spin_lock(PG_locked, &page->flags); +} + +static __always_inline void slab_unlock(struct page *page) +{ + __bit_spin_unlock(PG_locked, &page->flags); +} + static inline bool cmpxchg_double_slab(struct kmem_cache *s, struct page *page, void *freelist_old, unsigned long counters_old, void *freelist_new, unsigned long counters_new, @@ -356,11 +368,14 @@ static inline bool cmpxchg_double_slab(struct kmem_cache *s, struct page *page, } else #endif { + slab_lock(page); if (page->freelist == freelist_old && page->counters == counters_old) { page->freelist = freelist_new; page->counters = counters_new; + slab_unlock(page); return 1; } + slab_unlock(page); } cpu_relax(); @@ -377,7 +392,7 @@ static inline bool cmpxchg_double_slab(struct kmem_cache *s, struct page *page, /* * Determine a map of object in use on a page. * - * Slab lock or node listlock must be held to guarantee that the page does + * Node listlock must be held to guarantee that the page does * not vanish from under us. */ static void get_map(struct kmem_cache *s, struct page *page, unsigned long *map) @@ -808,10 +823,11 @@ static int check_slab(struct kmem_cache *s, struct page *page) static int on_freelist(struct kmem_cache *s, struct page *page, void *search) { int nr = 0; - void *fp = page->freelist; + void *fp; void *object = NULL; unsigned long max_objects; + fp = page->freelist; while (fp && nr <= page->objects) { if (fp == search) return 1; @@ -1024,6 +1040,8 @@ bad: static noinline int free_debug_processing(struct kmem_cache *s, struct page *page, void *object, unsigned long addr) { + slab_lock(page); + if (!check_slab(s, page)) goto fail; @@ -1059,10 +1077,12 @@ static noinline int free_debug_processing(struct kmem_cache *s, set_track(s, object, TRACK_FREE, addr); trace(s, page, object, 0); init_object(s, object, SLUB_RED_INACTIVE); + slab_unlock(page); return 1; fail: slab_fix(s, "Object at 0x%p not freed", object); + slab_unlock(page); return 0; } @@ -1394,27 +1414,6 @@ static void discard_slab(struct kmem_cache *s, struct page *page) } /* - * Per slab locking using the pagelock - */ -static __always_inline void slab_lock(struct page *page) -{ - bit_spin_lock(PG_locked, &page->flags); -} - -static __always_inline void slab_unlock(struct page *page) -{ - __bit_spin_unlock(PG_locked, &page->flags); -} - -static __always_inline int slab_trylock(struct page *page) -{ - int rc = 1; - - rc = bit_spin_trylock(PG_locked, &page->flags); - return rc; -} - -/* * Management of partially allocated slabs. * * list_lock must be held. @@ -1445,17 +1444,13 @@ static inline void remove_partial(struct kmem_cache_node *n, * * Must hold list_lock. */ -static inline int lock_and_freeze_slab(struct kmem_cache *s, +static inline int acquire_slab(struct kmem_cache *s, struct kmem_cache_node *n, struct page *page) { void *freelist; unsigned long counters; struct page new; - - if (!slab_trylock(page)) - return 0; - /* * Zap the freelist and set the frozen bit. * The old freelist is the list of objects for the @@ -1491,7 +1486,6 @@ static inline int lock_and_freeze_slab(struct kmem_cache *s, */ printk(KERN_ERR "SLUB: %s : Page without available objects on" " partial list\n", s->name); - slab_unlock(page); return 0; } } @@ -1515,7 +1509,7 @@ static struct page *get_partial_node(struct kmem_cache *s, spin_lock(&n->list_lock); list_for_each_entry(page, &n->partial, lru) - if (lock_and_freeze_slab(s, n, page)) + if (acquire_slab(s, n, page)) goto out; page = NULL; out: @@ -1804,8 +1798,6 @@ redo: "unfreezing slab")) goto redo; - slab_unlock(page); - if (lock) spin_unlock(&n->list_lock); @@ -1819,7 +1811,6 @@ redo: static inline void flush_slab(struct kmem_cache *s, struct kmem_cache_cpu *c) { stat(s, CPUSLAB_FLUSH); - slab_lock(c->page); deactivate_slab(s, c); } @@ -1968,7 +1959,6 @@ static void *__slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node, if (!page) goto new_slab; - slab_lock(page); if (unlikely(!node_match(c, node))) goto another_slab; @@ -1994,8 +1984,6 @@ load_freelist: stat(s, ALLOC_REFILL); - slab_unlock(page); - c->freelist = get_freepointer(s, object); c->tid = next_tid(c->tid); local_irq_restore(flags); @@ -2031,7 +2019,6 @@ new_slab: page->inuse = page->objects; stat(s, ALLOC_SLAB); - slab_lock(page); c->node = page_to_nid(page); c->page = page; goto load_freelist; @@ -2205,7 +2192,6 @@ static void __slab_free(struct kmem_cache *s, struct page *page, unsigned long uninitialized_var(flags); local_irq_save(flags); - slab_lock(page); stat(s, FREE_SLOWPATH); if (kmem_cache_debug(s) && !free_debug_processing(s, page, x, addr)) @@ -2271,7 +2257,6 @@ static void __slab_free(struct kmem_cache *s, struct page *page, spin_unlock(&n->list_lock); out_unlock: - slab_unlock(page); local_irq_restore(flags); return; @@ -2285,7 +2270,6 @@ slab_empty: } spin_unlock(&n->list_lock); - slab_unlock(page); local_irq_restore(flags); stat(s, FREE_SLAB); discard_slab(s, page); @@ -3202,14 +3186,8 @@ int kmem_cache_shrink(struct kmem_cache *s) * list_lock. page->inuse here is the upper limit. */ list_for_each_entry_safe(page, t, &n->partial, lru) { - if (!page->inuse && slab_trylock(page)) { - /* - * Must hold slab lock here because slab_free - * may have freed the last object and be - * waiting to release the slab. - */ + if (!page->inuse) { remove_partial(n, page); - slab_unlock(page); discard_slab(s, page); } else { list_move(&page->lru, @@ -3797,12 +3775,9 @@ static int validate_slab(struct kmem_cache *s, struct page *page, static void validate_slab_slab(struct kmem_cache *s, struct page *page, unsigned long *map) { - if (slab_trylock(page)) { - validate_slab(s, page, map); - slab_unlock(page); - } else - printk(KERN_INFO "SLUB %s: Skipped busy slab 0x%p\n", - s->name, page); + slab_lock(page); + validate_slab(s, page, map); + slab_unlock(page); } static int validate_slab_node(struct kmem_cache *s, |