diff options
Diffstat (limited to 'fs/mbcache.c')
| -rw-r--r-- | fs/mbcache.c | 630 |
1 files changed, 630 insertions, 0 deletions
diff --git a/fs/mbcache.c b/fs/mbcache.c new file mode 100644 index 00000000..93444747 --- /dev/null +++ b/fs/mbcache.c @@ -0,0 +1,630 @@ +/* + * 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 + +struct mb_cache { + struct list_head c_cache_list; + const char *c_name; + atomic_t c_entry_count; + int c_max_entries; + int c_bucket_bits; + struct kmem_cache *c_entry_cache; + struct list_head *c_block_hash; + struct list_head *c_index_hash; +}; + + +/* + * 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, int nr_to_scan, gfp_t gfp_mask); + +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) + * @nr_to_scan: Number of objects to scan + * @gfp_mask: (ignored) + * + * Returns the number of objects which are present in the cache. + */ +static int +mb_cache_shrink_fn(struct shrinker *shrink, int nr_to_scan, gfp_t gfp_mask) +{ + LIST_HEAD(free_list); + struct mb_cache *cache; + struct mb_cache_entry *entry, *tmp; + int count = 0; + + 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. Additonal 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) + |