diff options
Diffstat (limited to 'kernel/fs/mbcache.c')
| -rw-r--r-- | kernel/fs/mbcache.c | 858 |
1 files changed, 858 insertions, 0 deletions
diff --git a/kernel/fs/mbcache.c b/kernel/fs/mbcache.c new file mode 100644 index 000000000..187477ded --- /dev/null +++ b/kernel/fs/mbcache.c @@ -0,0 +1,858 @@ +/* + * 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. + */ + +/* + * Lock descriptions and usage: + * + * Each hash chain of both the block and index hash tables now contains + * a built-in lock used to serialize accesses to the hash chain. + * + * Accesses to global data structures mb_cache_list and mb_cache_lru_list + * are serialized via the global spinlock mb_cache_spinlock. + * + * Each mb_cache_entry contains a spinlock, e_entry_lock, to serialize + * accesses to its local data, such as e_used and e_queued. + * + * Lock ordering: + * + * Each block hash chain's lock has the highest lock order, followed by an + * index hash chain's lock, mb_cache_bg_lock (used to implement mb_cache_entry's + * lock), and mb_cach_spinlock, with the lowest order. While holding + * either a block or index hash chain lock, a thread can acquire an + * mc_cache_bg_lock, which in turn can also acquire mb_cache_spinlock. + * + * Synchronization: + * + * Since both mb_cache_entry_get and mb_cache_entry_find scan the block and + * index hash chian, it needs to lock the corresponding hash chain. For each + * mb_cache_entry within the chain, it needs to lock the mb_cache_entry to + * prevent either any simultaneous release or free on the entry and also + * to serialize accesses to either the e_used or e_queued member of the entry. + * + * To avoid having a dangling reference to an already freed + * mb_cache_entry, an mb_cache_entry is only freed when it is not on a + * block hash chain and also no longer being referenced, both e_used, + * and e_queued are 0's. When an mb_cache_entry is explicitly freed it is + * first removed from a block hash chain. + */ + +#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/list_bl.h> +#include <linux/mbcache.h> +#include <linux/init.h> +#include <linux/blockgroup_lock.h> +#include <linux/log2.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) + +#define MB_CACHE_ENTRY_LOCK_BITS ilog2(NR_BG_LOCKS) +#define MB_CACHE_ENTRY_LOCK_INDEX(ce) \ + (hash_long((unsigned long)ce, MB_CACHE_ENTRY_LOCK_BITS)) + +static DECLARE_WAIT_QUEUE_HEAD(mb_cache_queue); +static struct blockgroup_lock *mb_cache_bg_lock; +static struct kmem_cache *mb_cache_kmem_cache; + +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); + +static inline void +__spin_lock_mb_cache_entry(struct mb_cache_entry *ce) +{ + spin_lock(bgl_lock_ptr(mb_cache_bg_lock, + MB_CACHE_ENTRY_LOCK_INDEX(ce))); +} + +static inline void +__spin_unlock_mb_cache_entry(struct mb_cache_entry *ce) +{ + spin_unlock(bgl_lock_ptr(mb_cache_bg_lock, + MB_CACHE_ENTRY_LOCK_INDEX(ce))); +} + +static inline int +__mb_cache_entry_is_block_hashed(struct mb_cache_entry *ce) +{ + return !hlist_bl_unhashed(&ce->e_block_list); +} + + +static inline void +__mb_cache_entry_unhash_block(struct mb_cache_entry *ce) +{ + if (__mb_cache_entry_is_block_hashed(ce)) + hlist_bl_del_init(&ce->e_block_list); +} + +static inline int +__mb_cache_entry_is_index_hashed(struct mb_cache_entry *ce) +{ + return !hlist_bl_unhashed(&ce->e_index.o_list); +} + +static inline void +__mb_cache_entry_unhash_index(struct mb_cache_entry *ce) +{ + if (__mb_cache_entry_is_index_hashed(ce)) + hlist_bl_del_init(&ce->e_index.o_list); +} + +/* + * __mb_cache_entry_unhash_unlock() + * + * This function is called to unhash both the block and index hash + * chain. + * It assumes both the block and index hash chain is locked upon entry. + * It also unlock both hash chains both exit + */ +static inline void +__mb_cache_entry_unhash_unlock(struct mb_cache_entry *ce) +{ + __mb_cache_entry_unhash_index(ce); + hlist_bl_unlock(ce->e_index_hash_p); + __mb_cache_entry_unhash_block(ce); + hlist_bl_unlock(ce->e_block_hash_p); +} + +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 || atomic_read(&ce->e_refcnt))); + kmem_cache_free(cache->c_entry_cache, ce); + atomic_dec(&cache->c_entry_count); +} + +static void +__mb_cache_entry_release(struct mb_cache_entry *ce) +{ + /* First lock the entry to serialize access to its local data. */ + __spin_lock_mb_cache_entry(ce); + /* 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; + /* + * Make sure that all cache entries on lru_list have + * both e_used and e_qued of 0s. + */ + ce->e_used--; + if (!(ce->e_used || ce->e_queued || atomic_read(&ce->e_refcnt))) { + if (!__mb_cache_entry_is_block_hashed(ce)) { + __spin_unlock_mb_cache_entry(ce); + goto forget; + } + /* + * Need access to lru list, first drop entry lock, + * then reacquire the lock in the proper order. + */ + spin_lock(&mb_cache_spinlock); + if (list_empty(&ce->e_lru_list)) + list_add_tail(&ce->e_lru_list, &mb_cache_lru_list); + spin_unlock(&mb_cache_spinlock); + } + __spin_unlock_mb_cache_entry(ce); + return; +forget: + mb_assert(list_empty(&ce->e_lru_list)); + __mb_cache_entry_forget(ce, GFP_KERNEL); +} + +/* + * mb_cache_shrink_scan() 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 freed. + */ +static unsigned long +mb_cache_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) +{ + LIST_HEAD(free_list); + struct mb_cache_entry *entry, *tmp; + int nr_to_scan = sc->nr_to_scan; + gfp_t gfp_mask = sc->gfp_mask; + unsigned long freed = 0; + + mb_debug("trying to free %d entries", nr_to_scan); + spin_lock(&mb_cache_spinlock); + while ((nr_to_scan-- > 0) && !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_del_init(&ce->e_lru_list); + if (ce->e_used || ce->e_queued || atomic_read(&ce->e_refcnt)) + continue; + spin_unlock(&mb_cache_spinlock); + /* Prevent any find or get operation on the entry */ + hlist_bl_lock(ce->e_block_hash_p); + hlist_bl_lock(ce->e_index_hash_p); + /* Ignore if it is touched by a find/get */ + if (ce->e_used || ce->e_queued || atomic_read(&ce->e_refcnt) || + !list_empty(&ce->e_lru_list)) { + hlist_bl_unlock(ce->e_index_hash_p); + hlist_bl_unlock(ce->e_block_hash_p); + spin_lock(&mb_cache_spinlock); + continue; + } + __mb_cache_entry_unhash_unlock(ce); + list_add_tail(&ce->e_lru_list, &free_list); + spin_lock(&mb_cache_spinlock); + } + spin_unlock(&mb_cache_spinlock); + + list_for_each_entry_safe(entry, tmp, &free_list, e_lru_list) { + __mb_cache_entry_forget(entry, gfp_mask); + freed++; + } + return freed; +} + +static unsigned long +mb_cache_shrink_count(struct shrinker *shrink, struct shrink_control *sc) +{ + struct mb_cache *cache; + unsigned long count = 0; + + spin_lock(&mb_cache_spinlock); + 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); + + return vfs_pressure_ratio(count); +} + +static struct shrinker mb_cache_shrinker = { + .count_objects = mb_cache_shrink_count, + .scan_objects = mb_cache_shrink_scan, + .seeks = DEFAULT_SEEKS, +}; + +/* + * 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; + + if (!mb_cache_bg_lock) { + mb_cache_bg_lock = kmalloc(sizeof(struct blockgroup_lock), + GFP_KERNEL); + if (!mb_cache_bg_lock) + return NULL; + bgl_lock_init(mb_cache_bg_lock); + } + + 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 hlist_bl_head), GFP_KERNEL); + if (!cache->c_block_hash) + goto fail; + for (n=0; n<bucket_count; n++) + INIT_HLIST_BL_HEAD(&cache->c_block_hash[n]); + cache->c_index_hash = kmalloc(bucket_count * + sizeof(struct hlist_bl_head), GFP_KERNEL); + if (!cache->c_index_hash) + goto fail; + for (n=0; n<bucket_count; n++) + INIT_HLIST_BL_HEAD(&cache->c_index_hash[n]); + if (!mb_cache_kmem_cache) { + mb_cache_kmem_cache = kmem_cache_create(name, + sizeof(struct mb_cache_entry), 0, + SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD, NULL); + if (!mb_cache_kmem_cache) + goto fail2; + } + cache->c_entry_cache = mb_cache_kmem_cache; + + /* + * 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; + struct mb_cache_entry *ce, *tmp; + + l = &mb_cache_lru_list; + spin_lock(&mb_cache_spinlock); + while (!list_is_last(l, &mb_cache_lru_list)) { + l = l->next; + ce = list_entry(l, struct mb_cache_entry, e_lru_list); + if (ce->e_bdev == bdev) { + list_del_init(&ce->e_lru_list); + if (ce->e_used || ce->e_queued || + atomic_read(&ce->e_refcnt)) + continue; + spin_unlock(&mb_cache_spinlock); + /* + * Prevent any find or get operation on the entry. + */ + hlist_bl_lock(ce->e_block_hash_p); + hlist_bl_lock(ce->e_index_hash_p); + /* Ignore if it is touched by a find/get */ + if (ce->e_used || ce->e_queued || + atomic_read(&ce->e_refcnt) || + !list_empty(&ce->e_lru_list)) { + hlist_bl_unlock(ce->e_index_hash_p); + hlist_bl_unlock(ce->e_block_hash_p); + l = &mb_cache_lru_list; + spin_lock(&mb_cache_spinlock); + continue; + } + __mb_cache_entry_unhash_unlock(ce); + mb_assert(!(ce->e_used || ce->e_queued || + atomic_read(&ce->e_refcnt))); + list_add_tail(&ce->e_lru_list, &free_list); + l = &mb_cache_lru_list; + spin_lock(&mb_cache_spinlock); + } + } + spin_unlock(&mb_cache_spinlock); + + list_for_each_entry_safe(ce, tmp, &free_list, e_lru_list) { + __mb_cache_entry_forget(ce, 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 mb_cache_entry *ce, *tmp; + + spin_lock(&mb_cache_spinlock); + list_for_each_entry_safe(ce, tmp, &mb_cache_lru_list, e_lru_list) { + if (ce->e_cache == cache) + list_move_tail(&ce->e_lru_list, &free_list); + } + list_del(&cache->c_cache_list); + spin_unlock(&mb_cache_spinlock); + + list_for_each_entry_safe(ce, tmp, &free_list, e_lru_list) { + list_del_init(&ce->e_lru_list); + /* + * Prevent any find or get operation on the entry. + */ + hlist_bl_lock(ce->e_block_hash_p); + hlist_bl_lock(ce->e_index_hash_p); + mb_assert(!(ce->e_used || ce->e_queued || + atomic_read(&ce->e_refcnt))); + __mb_cache_entry_unhash_unlock(ce); + __mb_cache_entry_forget(ce, 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)); + } + + if (list_empty(&mb_cache_list)) { + kmem_cache_destroy(mb_cache_kmem_cache); + mb_cache_kmem_cache = NULL; + } + 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; + + if (atomic_read(&cache->c_entry_count) >= cache->c_max_entries) { + struct list_head *l; + + l = &mb_cache_lru_list; + spin_lock(&mb_cache_spinlock); + while (!list_is_last(l, &mb_cache_lru_list)) { + l = l->next; + ce = list_entry(l, struct mb_cache_entry, e_lru_list); + if (ce->e_cache == cache) { + list_del_init(&ce->e_lru_list); + if (ce->e_used || ce->e_queued || + atomic_read(&ce->e_refcnt)) + continue; + spin_unlock(&mb_cache_spinlock); + /* + * Prevent any find or get operation on the + * entry. + */ + hlist_bl_lock(ce->e_block_hash_p); + hlist_bl_lock(ce->e_index_hash_p); + /* Ignore if it is touched by a find/get */ + if (ce->e_used || ce->e_queued || + atomic_read(&ce->e_refcnt) || + !list_empty(&ce->e_lru_list)) { + hlist_bl_unlock(ce->e_index_hash_p); + hlist_bl_unlock(ce->e_block_hash_p); + l = &mb_cache_lru_list; + spin_lock(&mb_cache_spinlock); + continue; + } + mb_assert(list_empty(&ce->e_lru_list)); + mb_assert(!(ce->e_used || ce->e_queued || + atomic_read(&ce->e_refcnt))); + __mb_cache_entry_unhash_unlock(ce); + goto found; + } + } + spin_unlock(&mb_cache_spinlock); + } + + 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_HLIST_BL_NODE(&ce->e_block_list); + INIT_HLIST_BL_NODE(&ce->e_index.o_list); + ce->e_cache = cache; + ce->e_queued = 0; + atomic_set(&ce->e_refcnt, 0); +found: + ce->e_block_hash_p = &cache->c_block_hash[0]; + ce->e_index_hash_p = &cache->c_index_hash[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 hlist_bl_node *l; + struct hlist_bl_head *block_hash_p; + struct hlist_bl_head *index_hash_p; + struct mb_cache_entry *lce; + + mb_assert(ce); + bucket = hash_long((unsigned long)bdev + (block & 0xffffffff), + cache->c_bucket_bits); + block_hash_p = &cache->c_block_hash[bucket]; + hlist_bl_lock(block_hash_p); + hlist_bl_for_each_entry(lce, l, block_hash_p, e_block_list) { + if (lce->e_bdev == bdev && lce->e_block == block) { + hlist_bl_unlock(block_hash_p); + return -EBUSY; + } + } + mb_assert(!__mb_cache_entry_is_block_hashed(ce)); + __mb_cache_entry_unhash_block(ce); + __mb_cache_entry_unhash_index(ce); + ce->e_bdev = bdev; + ce->e_block = block; + ce->e_block_hash_p = block_hash_p; + ce->e_index.o_key = key; + hlist_bl_add_head(&ce->e_block_list, block_hash_p); + hlist_bl_unlock(block_hash_p); + bucket = hash_long(key, cache->c_bucket_bits); + index_hash_p = &cache->c_index_hash[bucket]; + hlist_bl_lock(index_hash_p); + ce->e_index_hash_p = index_hash_p; + hlist_bl_add_head(&ce->e_index.o_list, index_hash_p); + hlist_bl_unlock(index_hash_p); + return 0; +} + + +/* + * 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) +{ + __mb_cache_entry_release(ce); +} + + +/* + * mb_cache_entry_free() + * + */ +void +mb_cache_entry_free(struct mb_cache_entry *ce) +{ + mb_assert(ce); + mb_assert(list_empty(&ce->e_lru_list)); + hlist_bl_lock(ce->e_index_hash_p); + __mb_cache_entry_unhash_index(ce); + hlist_bl_unlock(ce->e_index_hash_p); + hlist_bl_lock(ce->e_block_hash_p); + __mb_cache_entry_unhash_block(ce); + hlist_bl_unlock(ce->e_block_hash_p); + __mb_cache_entry_release(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 hlist_bl_node *l; + struct mb_cache_entry *ce; + struct hlist_bl_head *block_hash_p; + + bucket = hash_long((unsigned long)bdev + (block & 0xffffffff), + cache->c_bucket_bits); + block_hash_p = &cache->c_block_hash[bucket]; + /* First serialize access to the block corresponding hash chain. */ + hlist_bl_lock(block_hash_p); + hlist_bl_for_each_entry(ce, l, block_hash_p, e_block_list) { + mb_assert(ce->e_block_hash_p == block_hash_p); + if (ce->e_bdev == bdev && ce->e_block == block) { + /* + * Prevent a free from removing the entry. + */ + atomic_inc(&ce->e_refcnt); + hlist_bl_unlock(block_hash_p); + __spin_lock_mb_cache_entry(ce); + atomic_dec(&ce->e_refcnt); + if (ce->e_used > 0) { + DEFINE_WAIT(wait); + while (ce->e_used > 0) { + ce->e_queued++; + prepare_to_wait(&mb_cache_queue, &wait, + TASK_UNINTERRUPTIBLE); + __spin_unlock_mb_cache_entry(ce); + schedule(); + __spin_lock_mb_cache_entry(ce); + ce->e_queued--; + } + finish_wait(&mb_cache_queue, &wait); + } + ce->e_used += 1 + MB_CACHE_WRITER; + __spin_unlock_mb_cache_entry(ce); + + if (!list_empty(&ce->e_lru_list)) { + spin_lock(&mb_cache_spinlock); + list_del_init(&ce->e_lru_list); + spin_unlock(&mb_cache_spinlock); + } + if (!__mb_cache_entry_is_block_hashed(ce)) { + __mb_cache_entry_release(ce); + return NULL; + } + return ce; + } + } + hlist_bl_unlock(block_hash_p); + return NULL; +} + +#if !defined(MB_CACHE_INDEXES_COUNT) || (MB_CACHE_INDEXES_COUNT > 0) + +static struct mb_cache_entry * +__mb_cache_entry_find(struct hlist_bl_node *l, struct hlist_bl_head *head, + struct block_device *bdev, unsigned int key) +{ + + /* The index hash chain is alredy acquire by caller. */ + while (l != NULL) { + struct mb_cache_entry *ce = + hlist_bl_entry(l, struct mb_cache_entry, + e_index.o_list); + mb_assert(ce->e_index_hash_p == head); + if (ce->e_bdev == bdev && ce->e_index.o_key == key) { + /* + * Prevent a free from removing the entry. + */ + atomic_inc(&ce->e_refcnt); + hlist_bl_unlock(head); + __spin_lock_mb_cache_entry(ce); + atomic_dec(&ce->e_refcnt); + ce->e_used++; + /* Incrementing before holding the lock gives readers + priority over writers. */ + if (ce->e_used >= MB_CACHE_WRITER) { + DEFINE_WAIT(wait); + + while (ce->e_used >= MB_CACHE_WRITER) { + ce->e_queued++; + prepare_to_wait(&mb_cache_queue, &wait, + TASK_UNINTERRUPTIBLE); + __spin_unlock_mb_cache_entry(ce); + schedule(); + __spin_lock_mb_cache_entry(ce); + ce->e_queued--; + } + finish_wait(&mb_cache_queue, &wait); + } + __spin_unlock_mb_cache_entry(ce); + if (!list_empty(&ce->e_lru_list)) { + spin_lock(&mb_cache_spinlock); + list_del_init(&ce->e_lru_list); + spin_unlock(&mb_cache_spinlock); + } + if (!__mb_cache_entry_is_block_hashed(ce)) { + __mb_cache_entry_release(ce); + return ERR_PTR(-EAGAIN); + } + return ce; + } + l = l->next; + } + hlist_bl_unlock(head); + 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 hlist_bl_node *l; + struct mb_cache_entry *ce = NULL; + struct hlist_bl_head *index_hash_p; + + index_hash_p = &cache->c_index_hash[bucket]; + hlist_bl_lock(index_hash_p); + if (!hlist_bl_empty(index_hash_p)) { + l = hlist_bl_first(index_hash_p); + ce = __mb_cache_entry_find(l, index_hash_p, bdev, key); + } else + hlist_bl_unlock(index_hash_p); + 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 hlist_bl_node *l; + struct mb_cache_entry *ce; + struct hlist_bl_head *index_hash_p; + + index_hash_p = &cache->c_index_hash[bucket]; + mb_assert(prev->e_index_hash_p == index_hash_p); + hlist_bl_lock(index_hash_p); + mb_assert(!hlist_bl_empty(index_hash_p)); + l = prev->e_index.o_list.next; + ce = __mb_cache_entry_find(l, index_hash_p, bdev, key); + __mb_cache_entry_release(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) + |