diff options
Diffstat (limited to 'fs/mbcache.c')
-rw-r--r-- | fs/mbcache.c | 445 |
1 files changed, 445 insertions, 0 deletions
diff --git a/fs/mbcache.c b/fs/mbcache.c new file mode 100644 index 0000000000..2a4b8b549e --- /dev/null +++ b/fs/mbcache.c @@ -0,0 +1,445 @@ +// SPDX-License-Identifier: GPL-2.0-only +#include <linux/spinlock.h> +#include <linux/slab.h> +#include <linux/list.h> +#include <linux/list_bl.h> +#include <linux/module.h> +#include <linux/sched.h> +#include <linux/workqueue.h> +#include <linux/mbcache.h> + +/* + * Mbcache is a simple key-value store. Keys need not be unique, however + * key-value pairs are expected to be unique (we use this fact in + * mb_cache_entry_delete_or_get()). + * + * Ext2 and ext4 use this cache for deduplication of extended attribute blocks. + * Ext4 also uses it for deduplication of xattr values stored in inodes. + * They use hash of data as a key and provide a value that may represent a + * block or inode number. That's why keys need not be unique (hash of different + * data may be the same). However user provided value always uniquely + * identifies a cache entry. + * + * We provide functions for creation and removal of entries, search by key, + * and a special "delete entry with given key-value pair" operation. Fixed + * size hash table is used for fast key lookups. + */ + +struct mb_cache { + /* Hash table of entries */ + struct hlist_bl_head *c_hash; + /* log2 of hash table size */ + int c_bucket_bits; + /* Maximum entries in cache to avoid degrading hash too much */ + unsigned long c_max_entries; + /* Protects c_list, c_entry_count */ + spinlock_t c_list_lock; + struct list_head c_list; + /* Number of entries in cache */ + unsigned long c_entry_count; + struct shrinker c_shrink; + /* Work for shrinking when the cache has too many entries */ + struct work_struct c_shrink_work; +}; + +static struct kmem_cache *mb_entry_cache; + +static unsigned long mb_cache_shrink(struct mb_cache *cache, + unsigned long nr_to_scan); + +static inline struct hlist_bl_head *mb_cache_entry_head(struct mb_cache *cache, + u32 key) +{ + return &cache->c_hash[hash_32(key, cache->c_bucket_bits)]; +} + +/* + * Number of entries to reclaim synchronously when there are too many entries + * in cache + */ +#define SYNC_SHRINK_BATCH 64 + +/* + * mb_cache_entry_create - create entry in cache + * @cache - cache where the entry should be created + * @mask - gfp mask with which the entry should be allocated + * @key - key of the entry + * @value - value of the entry + * @reusable - is the entry reusable by others? + * + * Creates entry in @cache with key @key and value @value. The function returns + * -EBUSY if entry with the same key and value already exists in cache. + * Otherwise 0 is returned. + */ +int mb_cache_entry_create(struct mb_cache *cache, gfp_t mask, u32 key, + u64 value, bool reusable) +{ + struct mb_cache_entry *entry, *dup; + struct hlist_bl_node *dup_node; + struct hlist_bl_head *head; + + /* Schedule background reclaim if there are too many entries */ + if (cache->c_entry_count >= cache->c_max_entries) + schedule_work(&cache->c_shrink_work); + /* Do some sync reclaim if background reclaim cannot keep up */ + if (cache->c_entry_count >= 2*cache->c_max_entries) + mb_cache_shrink(cache, SYNC_SHRINK_BATCH); + + entry = kmem_cache_alloc(mb_entry_cache, mask); + if (!entry) + return -ENOMEM; + + INIT_LIST_HEAD(&entry->e_list); + /* + * We create entry with two references. One reference is kept by the + * hash table, the other reference is used to protect us from + * mb_cache_entry_delete_or_get() until the entry is fully setup. This + * avoids nesting of cache->c_list_lock into hash table bit locks which + * is problematic for RT. + */ + atomic_set(&entry->e_refcnt, 2); + entry->e_key = key; + entry->e_value = value; + entry->e_flags = 0; + if (reusable) + set_bit(MBE_REUSABLE_B, &entry->e_flags); + head = mb_cache_entry_head(cache, key); + hlist_bl_lock(head); + hlist_bl_for_each_entry(dup, dup_node, head, e_hash_list) { + if (dup->e_key == key && dup->e_value == value) { + hlist_bl_unlock(head); + kmem_cache_free(mb_entry_cache, entry); + return -EBUSY; + } + } + hlist_bl_add_head(&entry->e_hash_list, head); + hlist_bl_unlock(head); + spin_lock(&cache->c_list_lock); + list_add_tail(&entry->e_list, &cache->c_list); + cache->c_entry_count++; + spin_unlock(&cache->c_list_lock); + mb_cache_entry_put(cache, entry); + + return 0; +} +EXPORT_SYMBOL(mb_cache_entry_create); + +void __mb_cache_entry_free(struct mb_cache *cache, struct mb_cache_entry *entry) +{ + struct hlist_bl_head *head; + + head = mb_cache_entry_head(cache, entry->e_key); + hlist_bl_lock(head); + hlist_bl_del(&entry->e_hash_list); + hlist_bl_unlock(head); + kmem_cache_free(mb_entry_cache, entry); +} +EXPORT_SYMBOL(__mb_cache_entry_free); + +/* + * mb_cache_entry_wait_unused - wait to be the last user of the entry + * + * @entry - entry to work on + * + * Wait to be the last user of the entry. + */ +void mb_cache_entry_wait_unused(struct mb_cache_entry *entry) +{ + wait_var_event(&entry->e_refcnt, atomic_read(&entry->e_refcnt) <= 2); +} +EXPORT_SYMBOL(mb_cache_entry_wait_unused); + +static struct mb_cache_entry *__entry_find(struct mb_cache *cache, + struct mb_cache_entry *entry, + u32 key) +{ + struct mb_cache_entry *old_entry = entry; + struct hlist_bl_node *node; + struct hlist_bl_head *head; + + head = mb_cache_entry_head(cache, key); + hlist_bl_lock(head); + if (entry && !hlist_bl_unhashed(&entry->e_hash_list)) + node = entry->e_hash_list.next; + else + node = hlist_bl_first(head); + while (node) { + entry = hlist_bl_entry(node, struct mb_cache_entry, + e_hash_list); + if (entry->e_key == key && + test_bit(MBE_REUSABLE_B, &entry->e_flags) && + atomic_inc_not_zero(&entry->e_refcnt)) + goto out; + node = node->next; + } + entry = NULL; +out: + hlist_bl_unlock(head); + if (old_entry) + mb_cache_entry_put(cache, old_entry); + + return entry; +} + +/* + * mb_cache_entry_find_first - find the first reusable entry with the given key + * @cache: cache where we should search + * @key: key to look for + * + * Search in @cache for a reusable entry with key @key. Grabs reference to the + * first reusable entry found and returns the entry. + */ +struct mb_cache_entry *mb_cache_entry_find_first(struct mb_cache *cache, + u32 key) +{ + return __entry_find(cache, NULL, key); +} +EXPORT_SYMBOL(mb_cache_entry_find_first); + +/* + * mb_cache_entry_find_next - find next reusable entry with the same key + * @cache: cache where we should search + * @entry: entry to start search from + * + * Finds next reusable entry in the hash chain which has the same key as @entry. + * If @entry is unhashed (which can happen when deletion of entry races with the + * search), finds the first reusable entry in the hash chain. The function drops + * reference to @entry and returns with a reference to the found entry. + */ +struct mb_cache_entry *mb_cache_entry_find_next(struct mb_cache *cache, + struct mb_cache_entry *entry) +{ + return __entry_find(cache, entry, entry->e_key); +} +EXPORT_SYMBOL(mb_cache_entry_find_next); + +/* + * mb_cache_entry_get - get a cache entry by value (and key) + * @cache - cache we work with + * @key - key + * @value - value + */ +struct mb_cache_entry *mb_cache_entry_get(struct mb_cache *cache, u32 key, + u64 value) +{ + struct hlist_bl_node *node; + struct hlist_bl_head *head; + struct mb_cache_entry *entry; + + head = mb_cache_entry_head(cache, key); + hlist_bl_lock(head); + hlist_bl_for_each_entry(entry, node, head, e_hash_list) { + if (entry->e_key == key && entry->e_value == value && + atomic_inc_not_zero(&entry->e_refcnt)) + goto out; + } + entry = NULL; +out: + hlist_bl_unlock(head); + return entry; +} +EXPORT_SYMBOL(mb_cache_entry_get); + +/* mb_cache_entry_delete_or_get - remove a cache entry if it has no users + * @cache - cache we work with + * @key - key + * @value - value + * + * Remove entry from cache @cache with key @key and value @value. The removal + * happens only if the entry is unused. The function returns NULL in case the + * entry was successfully removed or there's no entry in cache. Otherwise the + * function grabs reference of the entry that we failed to delete because it + * still has users and return it. + */ +struct mb_cache_entry *mb_cache_entry_delete_or_get(struct mb_cache *cache, + u32 key, u64 value) +{ + struct mb_cache_entry *entry; + + entry = mb_cache_entry_get(cache, key, value); + if (!entry) + return NULL; + + /* + * Drop the ref we got from mb_cache_entry_get() and the initial hash + * ref if we are the last user + */ + if (atomic_cmpxchg(&entry->e_refcnt, 2, 0) != 2) + return entry; + + spin_lock(&cache->c_list_lock); + if (!list_empty(&entry->e_list)) + list_del_init(&entry->e_list); + cache->c_entry_count--; + spin_unlock(&cache->c_list_lock); + __mb_cache_entry_free(cache, entry); + return NULL; +} +EXPORT_SYMBOL(mb_cache_entry_delete_or_get); + +/* mb_cache_entry_touch - cache entry got used + * @cache - cache the entry belongs to + * @entry - entry that got used + * + * Marks entry as used to give hit higher chances of surviving in cache. + */ +void mb_cache_entry_touch(struct mb_cache *cache, + struct mb_cache_entry *entry) +{ + set_bit(MBE_REFERENCED_B, &entry->e_flags); +} +EXPORT_SYMBOL(mb_cache_entry_touch); + +static unsigned long mb_cache_count(struct shrinker *shrink, + struct shrink_control *sc) +{ + struct mb_cache *cache = container_of(shrink, struct mb_cache, + c_shrink); + + return cache->c_entry_count; +} + +/* Shrink number of entries in cache */ +static unsigned long mb_cache_shrink(struct mb_cache *cache, + unsigned long nr_to_scan) +{ + struct mb_cache_entry *entry; + unsigned long shrunk = 0; + + spin_lock(&cache->c_list_lock); + while (nr_to_scan-- && !list_empty(&cache->c_list)) { + entry = list_first_entry(&cache->c_list, + struct mb_cache_entry, e_list); + /* Drop initial hash reference if there is no user */ + if (test_bit(MBE_REFERENCED_B, &entry->e_flags) || + atomic_cmpxchg(&entry->e_refcnt, 1, 0) != 1) { + clear_bit(MBE_REFERENCED_B, &entry->e_flags); + list_move_tail(&entry->e_list, &cache->c_list); + continue; + } + list_del_init(&entry->e_list); + cache->c_entry_count--; + spin_unlock(&cache->c_list_lock); + __mb_cache_entry_free(cache, entry); + shrunk++; + cond_resched(); + spin_lock(&cache->c_list_lock); + } + spin_unlock(&cache->c_list_lock); + + return shrunk; +} + +static unsigned long mb_cache_scan(struct shrinker *shrink, + struct shrink_control *sc) +{ + struct mb_cache *cache = container_of(shrink, struct mb_cache, + c_shrink); + return mb_cache_shrink(cache, sc->nr_to_scan); +} + +/* We shrink 1/X of the cache when we have too many entries in it */ +#define SHRINK_DIVISOR 16 + +static void mb_cache_shrink_worker(struct work_struct *work) +{ + struct mb_cache *cache = container_of(work, struct mb_cache, + c_shrink_work); + mb_cache_shrink(cache, cache->c_max_entries / SHRINK_DIVISOR); +} + +/* + * mb_cache_create - create cache + * @bucket_bits: log2 of the hash table size + * + * Create cache for keys with 2^bucket_bits hash entries. + */ +struct mb_cache *mb_cache_create(int bucket_bits) +{ + struct mb_cache *cache; + unsigned long bucket_count = 1UL << bucket_bits; + unsigned long i; + + cache = kzalloc(sizeof(struct mb_cache), GFP_KERNEL); + if (!cache) + goto err_out; + cache->c_bucket_bits = bucket_bits; + cache->c_max_entries = bucket_count << 4; + INIT_LIST_HEAD(&cache->c_list); + spin_lock_init(&cache->c_list_lock); + cache->c_hash = kmalloc_array(bucket_count, + sizeof(struct hlist_bl_head), + GFP_KERNEL); + if (!cache->c_hash) { + kfree(cache); + goto err_out; + } + for (i = 0; i < bucket_count; i++) + INIT_HLIST_BL_HEAD(&cache->c_hash[i]); + + cache->c_shrink.count_objects = mb_cache_count; + cache->c_shrink.scan_objects = mb_cache_scan; + cache->c_shrink.seeks = DEFAULT_SEEKS; + if (register_shrinker(&cache->c_shrink, "mbcache-shrinker")) { + kfree(cache->c_hash); + kfree(cache); + goto err_out; + } + + INIT_WORK(&cache->c_shrink_work, mb_cache_shrink_worker); + + return cache; + +err_out: + return NULL; +} +EXPORT_SYMBOL(mb_cache_create); + +/* + * mb_cache_destroy - destroy cache + * @cache: the cache to destroy + * + * Free all entries in cache and cache itself. Caller must make sure nobody + * (except shrinker) can reach @cache when calling this. + */ +void mb_cache_destroy(struct mb_cache *cache) +{ + struct mb_cache_entry *entry, *next; + + unregister_shrinker(&cache->c_shrink); + + /* + * We don't bother with any locking. Cache must not be used at this + * point. + */ + list_for_each_entry_safe(entry, next, &cache->c_list, e_list) { + list_del(&entry->e_list); + WARN_ON(atomic_read(&entry->e_refcnt) != 1); + mb_cache_entry_put(cache, entry); + } + kfree(cache->c_hash); + kfree(cache); +} +EXPORT_SYMBOL(mb_cache_destroy); + +static int __init mbcache_init(void) +{ + mb_entry_cache = kmem_cache_create("mbcache", + sizeof(struct mb_cache_entry), 0, + SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD, NULL); + if (!mb_entry_cache) + return -ENOMEM; + return 0; +} + +static void __exit mbcache_exit(void) +{ + kmem_cache_destroy(mb_entry_cache); +} + +module_init(mbcache_init) +module_exit(mbcache_exit) + +MODULE_AUTHOR("Jan Kara <jack@suse.cz>"); +MODULE_DESCRIPTION("Meta block cache (for extended attributes)"); +MODULE_LICENSE("GPL"); |