/* * linux/fs/mbcache.c * (C) 2001-2002 Andreas Gruenbacher, <a.gruenbacher@computer.org> */ /* * Filesystem Meta Information Block Cache (mbcache) * * The mbcache caches blocks of block devices that need to be located * by their device/block number, as well as by other criteria (such * as the block's contents). * * There can only be one cache entry in a cache per device and block number. * Additional indexes need not be unique in this sense. The number of * additional indexes (=other criteria) can be hardwired at compile time * or specified at cache create time. * * Each cache entry is of fixed size. An entry may be `valid' or `invalid' * in the cache. A valid entry is in the main hash tables of the cache, * and may also be in the lru list. An invalid entry is not in any hashes * or lists. * * A valid cache entry is only in the lru list if no handles refer to it. * Invalid cache entries will be freed when the last handle to the cache * entry is released. Entries that cannot be freed immediately are put * back on the lru list. */ #include <linux/kernel.h> #include <linux/module.h> #include <linux/hash.h> #include <linux/fs.h> #include <linux/mm.h> #include <linux/slab.h> #include <linux/sched.h> #include <linux/init.h> #include <linux/mbcache.h> #ifdef MB_CACHE_DEBUG # define mb_debug(f...) do { \ printk(KERN_DEBUG f); \ printk("\n"); \ } while (0) #define mb_assert(c) do { if (!(c)) \ printk(KERN_ERR "assertion " #c " failed\n"); \ } while(0) #else # define mb_debug(f...) do { } while(0) # define mb_assert(c) do { } while(0) #endif #define mb_error(f...) do { \ printk(KERN_ERR f); \ printk("\n"); \ } while(0) #define MB_CACHE_WRITER ((unsigned short)~0U >> 1) static DECLARE_WAIT_QUEUE_HEAD(mb_cache_queue); MODULE_AUTHOR("Andreas Gruenbacher <a.gruenbacher@computer.org>"); MODULE_DESCRIPTION("Meta block cache (for extended attributes)"); MODULE_LICENSE("GPL"); EXPORT_SYMBOL(mb_cache_create); EXPORT_SYMBOL(mb_cache_shrink); EXPORT_SYMBOL(mb_cache_destroy); EXPORT_SYMBOL(mb_cache_entry_alloc); EXPORT_SYMBOL(mb_cache_entry_insert); EXPORT_SYMBOL(mb_cache_entry_release); EXPORT_SYMBOL(mb_cache_entry_free); EXPORT_SYMBOL(mb_cache_entry_get); #if !defined(MB_CACHE_INDEXES_COUNT) || (MB_CACHE_INDEXES_COUNT > 0) EXPORT_SYMBOL(mb_cache_entry_find_first); EXPORT_SYMBOL(mb_cache_entry_find_next); #endif /* * Global data: list of all mbcache's, lru list, and a spinlock for * accessing cache data structures on SMP machines. The lru list is * global across all mbcaches. */ static LIST_HEAD(mb_cache_list); static LIST_HEAD(mb_cache_lru_list); static DEFINE_SPINLOCK(mb_cache_spinlock); /* * What the mbcache registers as to get shrunk dynamically. */ static int mb_cache_shrink_fn(struct shrinker *shrink, struct shrink_control *sc); static struct shrinker mb_cache_shrinker = { .shrink = mb_cache_shrink_fn, .seeks = DEFAULT_SEEKS, }; static inline int __mb_cache_entry_is_hashed(struct mb_cache_entry *ce) { return !list_empty(&ce->e_block_list); } static void __mb_cache_entry_unhash(struct mb_cache_entry *ce) { if (__mb_cache_entry_is_hashed(ce)) { list_del_init(&ce->e_block_list); list_del(&ce->e_index.o_list); } } static void __mb_cache_entry_forget(struct mb_cache_entry *ce, gfp_t gfp_mask) { struct mb_cache *cache = ce->e_cache; mb_assert(!(ce->e_used || ce->e_queued)); kmem_cache_free(cache->c_entry_cache, ce); atomic_dec(&cache->c_entry_count); } static void __mb_cache_entry_release_unlock(struct mb_cache_entry *ce) __releases(mb_cache_spinlock) { /* Wake up all processes queuing for this cache entry. */ if (ce->e_queued) wake_up_all(&mb_cache_queue); if (ce->e_used >= MB_CACHE_WRITER) ce->e_used -= MB_CACHE_WRITER; ce->e_used--; if (!(ce->e_used || ce->e_queued)) { if (!__mb_cache_entry_is_hashed(ce)) goto forget; mb_assert(list_empty(&ce->e_lru_list)); list_add_tail(&ce->e_lru_list, &mb_cache_lru_list); } spin_unlock(&mb_cache_spinlock); return; forget: spin_unlock(&mb_cache_spinlock); __mb_cache_entry_forget(ce, GFP_KERNEL); } /* * mb_cache_shrink_fn() memory pressure callback * * This function is called by the kernel memory management when memory * gets low. * * @shrink: (ignored) * @sc: shrink_control passed from reclaim * * Returns the number of objects which are present in the cache. */ static int mb_cache_shrink_fn(struct shrinker *shrink, struct shrink_control *sc) { LIST_HEAD(free_list); struct mb_cache *cache; struct mb_cache_entry *entry, *tmp; int count = 0; int nr_to_scan = sc->nr_to_scan; gfp_t gfp_mask = sc->gfp_mask; mb_debug("trying to free %d entries", nr_to_scan); spin_lock(&mb_cache_spinlock); while (nr_to_scan-- && !list_empty(&mb_cache_lru_list)) { struct mb_cache_entry *ce = list_entry(mb_cache_lru_list.next, struct mb_cache_entry, e_lru_list); list_move_tail(&ce->e_lru_list, &free_list); __mb_cache_entry_unhash(ce); } list_for_each_entry(cache, &mb_cache_list, c_cache_list) { mb_debug("cache %s (%d)", cache->c_name, atomic_read(&cache->c_entry_count)); count += atomic_read(&cache->c_entry_count); } spin_unlock(&mb_cache_spinlock); list_for_each_entry_safe(entry, tmp, &free_list, e_lru_list) { __mb_cache_entry_forget(entry, gfp_mask); } return (count / 100) * sysctl_vfs_cache_pressure; } /* * mb_cache_create() create a new cache * * All entries in one cache are equal size. Cache entries may be from * multiple devices. If this is the first mbcache created, registers * the cache with kernel memory management. Returns NULL if no more * memory was available. * * @name: name of the cache (informal) * @bucket_bits: log2(number of hash buckets) */ struct mb_cache * mb_cache_create(const char *name, int bucket_bits) { int n, bucket_count = 1 << bucket_bits; struct mb_cache *cache = NULL; cache = kmalloc(sizeof(struct mb_cache), GFP_KERNEL); if (!cache) return NULL; cache->c_name = name; atomic_set(&cache->c_entry_count, 0); cache->c_bucket_bits = bucket_bits; cache->c_block_hash = kmalloc(bucket_count * sizeof(struct list_head), GFP_KERNEL); if (!cache->c_block_hash) goto fail; for (n=0; n<bucket_count; n++) INIT_LIST_HEAD(&cache->c_block_hash[n]); cache->c_index_hash = kmalloc(bucket_count * sizeof(struct list_head), GFP_KERNEL); if (!cache->c_index_hash) goto fail; for (n=0; n<bucket_count; n++) INIT_LIST_HEAD(&cache->c_index_hash[n]); cache->c_entry_cache = kmem_cache_create(name, sizeof(struct mb_cache_entry), 0, SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD, NULL); if (!cache->c_entry_cache) goto fail2; /* * Set an upper limit on the number of cache entries so that the hash * chains won't grow too long. */ cache->c_max_entries = bucket_count << 4; spin_lock(&mb_cache_spinlock); list_add(&cache->c_cache_list, &mb_cache_list); spin_unlock(&mb_cache_spinlock); return cache; fail2: kfree(cache->c_index_hash); fail: kfree(cache->c_block_hash); kfree(cache); return NULL; } /* * mb_cache_shrink() * * Removes all cache entries of a device from the cache. All cache entries * currently in use cannot be freed, and thus remain in the cache. All others * are freed. * * @bdev: which device's cache entries to shrink */ void mb_cache_shrink(struct block_device *bdev) { LIST_HEAD(free_list); struct list_head *l, *ltmp; spin_lock(&mb_cache_spinlock); list_for_each_safe(l, ltmp, &mb_cache_lru_list) { struct mb_cache_entry *ce = list_entry(l, struct mb_cache_entry, e_lru_list); if (ce->e_bdev == bdev) { list_move_tail(&ce->e_lru_list, &free_list); __mb_cache_entry_unhash(ce); } } spin_unlock(&mb_cache_spinlock); list_for_each_safe(l, ltmp, &free_list) { __mb_cache_entry_forget(list_entry(l, struct mb_cache_entry, e_lru_list), GFP_KERNEL); } } /* * mb_cache_destroy() * * Shrinks the cache to its minimum possible size (hopefully 0 entries), * and then destroys it. If this was the last mbcache, un-registers the * mbcache from kernel memory management. */ void mb_cache_destroy(struct mb_cache *cache) { LIST_HEAD(free_list); struct list_head *l, *ltmp; spin_lock(&mb_cache_spinlock); list_for_each_safe(l, ltmp, &mb_cache_lru_list) { struct mb_cache_entry *ce = list_entry(l, struct mb_cache_entry, e_lru_list); if (ce->e_cache == cache) { list_move_tail(&ce->e_lru_list, &free_list); __mb_cache_entry_unhash(ce); } } list_del(&cache->c_cache_list); spin_unlock(&mb_cache_spinlock); list_for_each_safe(l, ltmp, &free_list) { __mb_cache_entry_forget(list_entry(l, struct mb_cache_entry, e_lru_list), GFP_KERNEL); } if (atomic_read(&cache->c_entry_count) > 0) { mb_error("cache %s: %d orphaned entries", cache->c_name, atomic_read(&cache->c_entry_count)); } kmem_cache_destroy(cache->c_entry_cache); kfree(cache->c_index_hash); kfree(cache->c_block_hash); kfree(cache); } /* * mb_cache_entry_alloc() * * Allocates a new cache entry. The new entry will not be valid initially, * and thus cannot be looked up yet. It should be filled with data, and * then inserted into the cache using mb_cache_entry_insert(). Returns NULL * if no more memory was available. */ struct mb_cache_entry * mb_cache_entry_alloc(struct mb_cache *cache, gfp_t gfp_flags) { struct mb_cache_entry *ce = NULL; if (atomic_read(&cache->c_entry_count) >= cache->c_max_entries) { spin_lock(&mb_cache_spinlock); if (!list_empty(&mb_cache_lru_list)) { ce = list_entry(mb_cache_lru_list.next, struct mb_cache_entry, e_lru_list); list_del_init(&ce->e_lru_list); __mb_cache_entry_unhash(ce); } spin_unlock(&mb_cache_spinlock); } if (!ce) { ce = kmem_cache_alloc(cache->c_entry_cache, gfp_flags); if (!ce) return NULL; atomic_inc(&cache->c_entry_count); INIT_LIST_HEAD(&ce->e_lru_list); INIT_LIST_HEAD(&ce->e_block_list); ce->e_cache = cache; ce->e_queued = 0; } ce->e_used = 1 + MB_CACHE_WRITER; return ce; } /* * mb_cache_entry_insert() * * Inserts an entry that was allocated using mb_cache_entry_alloc() into * the cache. After this, the cache entry can be looked up, but is not yet * in the lru list as the caller still holds a handle to it. Returns 0 on * success, or -EBUSY if a cache entry for that device + inode exists * already (this may happen after a failed lookup, but when another process * has inserted the same cache entry in the meantime). * * @bdev: device the cache entry belongs to * @block: block number * @key: lookup key */ int mb_cache_entry_insert(struct mb_cache_entry *ce, struct block_device *bdev, sector_t block, unsigned int key) { struct mb_cache *cache = ce->e_cache; unsigned int bucket; struct list_head *l; int error = -EBUSY; bucket = hash_long((unsigned long)bdev + (block & 0xffffffff), cache->c_bucket_bits); spin_lock(&mb_cache_spinlock); list_for_each_prev(l, &cache->c_block_hash[bucket]) { struct mb_cache_entry *ce = list_entry(l, struct mb_cache_entry, e_block_list); if (ce->e_bdev == bdev && ce->e_block == block) goto out; } __mb_cache_entry_unhash(ce); ce->e_bdev = bdev; ce->e_block = block; list_add(&ce->e_block_list, &cache->c_block_hash[bucket]); ce->e_index.o_key = key; bucket = hash_long(key, cache->c_bucket_bits); list_add(&ce->e_index.o_list, &cache->c_index_hash[bucket]); error = 0; out: spin_unlock(&mb_cache_spinlock); return error; } /* * mb_cache_entry_release() * * Release a handle to a cache entry. When the last handle to a cache entry * is released it is either freed (if it is invalid) or otherwise inserted * in to the lru list. */ void mb_cache_entry_release(struct mb_cache_entry *ce) { spin_lock(&mb_cache_spinlock); __mb_cache_entry_release_unlock(ce); } /* * mb_cache_entry_free() * * This is equivalent to the sequence mb_cache_entry_takeout() -- * mb_cache_entry_release(). */ void mb_cache_entry_free(struct mb_cache_entry *ce) { spin_lock(&mb_cache_spinlock); mb_assert(list_empty(&ce->e_lru_list)); __mb_cache_entry_unhash(ce); __mb_cache_entry_release_unlock(ce); } /* * mb_cache_entry_get() * * Get a cache entry by device / block number. (There can only be one entry * in the cache per device and block.) Returns NULL if no such cache entry * exists. The returned cache entry is locked for exclusive access ("single * writer"). */ struct mb_cache_entry * mb_cache_entry_get(struct mb_cache *cache, struct block_device *bdev, sector_t block) { unsigned int bucket; struct list_head *l; struct mb_cache_entry *ce; bucket = hash_long((unsigned long)bdev + (block & 0xffffffff), cache->c_bucket_bits); spin_lock(&mb_cache_spinlock); list_for_each(l, &cache->c_block_hash[bucket]) { ce = list_entry(l, struct mb_cache_entry, e_block_list); if (ce->e_bdev == bdev && ce->e_block == block) { DEFINE_WAIT(wait); if (!list_empty(&ce->e_lru_list)) list_del_init(&ce->e_lru_list); while (ce->e_used > 0) { ce->e_queued++; prepare_to_wait(&mb_cache_queue, &wait, TASK_UNINTERRUPTIBLE); spin_unlock(&mb_cache_spinlock); schedule(); spin_lock(&mb_cache_spinlock); ce->e_queued--; } finish_wait(&mb_cache_queue, &wait); ce->e_used += 1 + MB_CACHE_WRITER; if (!__mb_cache_entry_is_hashed(ce)) { __mb_cache_entry_release_unlock(ce); return NULL; } goto cleanup; } } ce = NULL; cleanup: spin_unlock(&mb_cache_spinlock); return ce; } #if !defined(MB_CACHE_INDEXES_COUNT) || (MB_CACHE_INDEXES_COUNT > 0) static struct mb_cache_entry * __mb_cache_entry_find(struct list_head *l, struct list_head *head, struct block_device *bdev, unsigned int key) { while (l != head) { struct mb_cache_entry *ce = list_entry(l, struct mb_cache_entry, e_index.o_list); if (ce->e_bdev == bdev && ce->e_index.o_key == key) { DEFINE_WAIT(wait); if (!list_empty(&ce->e_lru_list)) list_del_init(&ce->e_lru_list); /* Incrementing before holding the lock gives readers priority over writers. */ ce->e_used++; while (ce->e_used >= MB_CACHE_WRITER) { ce->e_queued++; prepare_to_wait(&mb_cache_queue, &wait, TASK_UNINTERRUPTIBLE); spin_unlock(&mb_cache_spinlock); schedule(); spin_lock(&mb_cache_spinlock); ce->e_queued--; } finish_wait(&mb_cache_queue, &wait); if (!__mb_cache_entry_is_hashed(ce)) { __mb_cache_entry_release_unlock(ce); spin_lock(&mb_cache_spinlock); return ERR_PTR(-EAGAIN); } return ce; } l = l->next; } return NULL; } /* * mb_cache_entry_find_first() * * Find the first cache entry on a given device with a certain key in * an additional index. Additional matches can be found with * mb_cache_entry_find_next(). Returns NULL if no match was found. The * returned cache entry is locked for shared access ("multiple readers"). * * @cache: the cache to search * @bdev: the device the cache entry should belong to * @key: the key in the index */ struct mb_cache_entry * mb_cache_entry_find_first(struct mb_cache *cache, struct block_device *bdev, unsigned int key) { unsigned int bucket = hash_long(key, cache->c_bucket_bits); struct list_head *l; struct mb_cache_entry *ce; spin_lock(&mb_cache_spinlock); l = cache->c_index_hash[bucket].next; ce = __mb_cache_entry_find(l, &cache->c_index_hash[bucket], bdev, key); spin_unlock(&mb_cache_spinlock); return ce; } /* * mb_cache_entry_find_next() * * Find the next cache entry on a given device with a certain key in an * additional index. Returns NULL if no match could be found. The previous * entry is atomatically released, so that mb_cache_entry_find_next() can * be called like this: * * entry = mb_cache_entry_find_first(); * while (entry) { * ... * entry = mb_cache_entry_find_next(entry, ...); * } * * @prev: The previous match * @bdev: the device the cache entry should belong to * @key: the key in the index */ struct mb_cache_entry * mb_cache_entry_find_next(struct mb_cache_entry *prev, struct block_device *bdev, unsigned int key) { struct mb_cache *cache = prev->e_cache; unsigned int bucket = hash_long(key, cache->c_bucket_bits); struct list_head *l; struct mb_cache_entry *ce; spin_lock(&mb_cache_spinlock); l = prev->e_index.o_list.next; ce = __mb_cache_entry_find(l, &cache->c_index_hash[bucket], bdev, key); __mb_cache_entry_release_unlock(prev); return ce; } #endif /* !defined(MB_CACHE_INDEXES_COUNT) || (MB_CACHE_INDEXES_COUNT > 0) */ static int __init init_mbcache(void) { register_shrinker(&mb_cache_shrinker); return 0; } static void __exit exit_mbcache(void) { unregister_shrinker(&mb_cache_shrinker); } module_init(init_mbcache) module_exit(exit_mbcache)