360 lines
10 KiB
C
360 lines
10 KiB
C
![]() |
#include <linux/spinlock.h>
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#include <linux/slab.h>
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#include <linux/list.h>
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#include <linux/list_bl.h>
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#include <linux/module.h>
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#include <linux/sched.h>
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#include <linux/mbcache2.h>
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/*
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* Mbcache is a simple key-value store. Keys need not be unique, however
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* key-value pairs are expected to be unique (we use this fact in
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* mb2_cache_entry_delete_block()).
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*
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* Ext2 and ext4 use this cache for deduplication of extended attribute blocks.
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* They use hash of a block contents as a key and block number as a value.
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* That's why keys need not be unique (different xattr blocks may end up having
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* the same hash). However block number always uniquely identifies a cache
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* entry.
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*
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* We provide functions for creation and removal of entries, search by key,
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* and a special "delete entry with given key-value pair" operation. Fixed
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* size hash table is used for fast key lookups.
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*/
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struct mb2_cache {
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/* Hash table of entries */
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struct hlist_bl_head *c_hash;
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/* log2 of hash table size */
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int c_bucket_bits;
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/* Protects c_lru_list, c_entry_count */
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spinlock_t c_lru_list_lock;
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struct list_head c_lru_list;
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/* Number of entries in cache */
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unsigned long c_entry_count;
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struct shrinker c_shrink;
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};
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static struct kmem_cache *mb2_entry_cache;
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/*
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* mb2_cache_entry_create - create entry in cache
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* @cache - cache where the entry should be created
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* @mask - gfp mask with which the entry should be allocated
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* @key - key of the entry
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* @block - block that contains data
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*
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* Creates entry in @cache with key @key and records that data is stored in
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* block @block. The function returns -EBUSY if entry with the same key
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* and for the same block already exists in cache. Otherwise 0 is returned.
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*/
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int mb2_cache_entry_create(struct mb2_cache *cache, gfp_t mask, u32 key,
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sector_t block)
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{
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struct mb2_cache_entry *entry, *dup;
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struct hlist_bl_node *dup_node;
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struct hlist_bl_head *head;
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entry = kmem_cache_alloc(mb2_entry_cache, mask);
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if (!entry)
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return -ENOMEM;
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INIT_LIST_HEAD(&entry->e_lru_list);
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/* One ref for hash, one ref returned */
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atomic_set(&entry->e_refcnt, 1);
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entry->e_key = key;
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entry->e_block = block;
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head = &cache->c_hash[hash_32(key, cache->c_bucket_bits)];
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entry->e_hash_list_head = head;
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hlist_bl_lock(head);
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hlist_bl_for_each_entry(dup, dup_node, head, e_hash_list) {
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if (dup->e_key == key && dup->e_block == block) {
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hlist_bl_unlock(head);
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kmem_cache_free(mb2_entry_cache, entry);
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return -EBUSY;
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}
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}
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hlist_bl_add_head(&entry->e_hash_list, head);
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hlist_bl_unlock(head);
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spin_lock(&cache->c_lru_list_lock);
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list_add_tail(&entry->e_lru_list, &cache->c_lru_list);
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/* Grab ref for LRU list */
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atomic_inc(&entry->e_refcnt);
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cache->c_entry_count++;
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spin_unlock(&cache->c_lru_list_lock);
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return 0;
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}
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EXPORT_SYMBOL(mb2_cache_entry_create);
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void __mb2_cache_entry_free(struct mb2_cache_entry *entry)
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{
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kmem_cache_free(mb2_entry_cache, entry);
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}
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EXPORT_SYMBOL(__mb2_cache_entry_free);
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static struct mb2_cache_entry *__entry_find(struct mb2_cache *cache,
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struct mb2_cache_entry *entry,
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u32 key)
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{
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struct mb2_cache_entry *old_entry = entry;
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struct hlist_bl_node *node;
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struct hlist_bl_head *head;
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if (entry)
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head = entry->e_hash_list_head;
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else
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head = &cache->c_hash[hash_32(key, cache->c_bucket_bits)];
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hlist_bl_lock(head);
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if (entry && !hlist_bl_unhashed(&entry->e_hash_list))
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node = entry->e_hash_list.next;
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else
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node = hlist_bl_first(head);
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while (node) {
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entry = hlist_bl_entry(node, struct mb2_cache_entry,
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e_hash_list);
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if (entry->e_key == key) {
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atomic_inc(&entry->e_refcnt);
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goto out;
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}
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node = node->next;
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}
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entry = NULL;
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out:
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hlist_bl_unlock(head);
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if (old_entry)
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mb2_cache_entry_put(cache, old_entry);
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return entry;
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}
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/*
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* mb2_cache_entry_find_first - find the first entry in cache with given key
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* @cache: cache where we should search
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* @key: key to look for
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*
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* Search in @cache for entry with key @key. Grabs reference to the first
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* entry found and returns the entry.
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*/
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struct mb2_cache_entry *mb2_cache_entry_find_first(struct mb2_cache *cache,
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u32 key)
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{
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return __entry_find(cache, NULL, key);
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}
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EXPORT_SYMBOL(mb2_cache_entry_find_first);
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/*
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* mb2_cache_entry_find_next - find next entry in cache with the same
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* @cache: cache where we should search
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* @entry: entry to start search from
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*
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* Finds next entry in the hash chain which has the same key as @entry.
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* If @entry is unhashed (which can happen when deletion of entry races
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* with the search), finds the first entry in the hash chain. The function
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* drops reference to @entry and returns with a reference to the found entry.
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*/
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struct mb2_cache_entry *mb2_cache_entry_find_next(struct mb2_cache *cache,
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struct mb2_cache_entry *entry)
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{
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return __entry_find(cache, entry, entry->e_key);
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}
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EXPORT_SYMBOL(mb2_cache_entry_find_next);
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/* mb2_cache_entry_delete_block - remove information about block from cache
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* @cache - cache we work with
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* @key - key of the entry to remove
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* @block - block containing data for @key
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*
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* Remove entry from cache @cache with key @key with data stored in @block.
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*/
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void mb2_cache_entry_delete_block(struct mb2_cache *cache, u32 key,
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sector_t block)
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{
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struct hlist_bl_node *node;
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struct hlist_bl_head *head;
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struct mb2_cache_entry *entry;
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head = &cache->c_hash[hash_32(key, cache->c_bucket_bits)];
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hlist_bl_lock(head);
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hlist_bl_for_each_entry(entry, node, head, e_hash_list) {
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if (entry->e_key == key && entry->e_block == block) {
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/* We keep hash list reference to keep entry alive */
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hlist_bl_del_init(&entry->e_hash_list);
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hlist_bl_unlock(head);
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spin_lock(&cache->c_lru_list_lock);
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if (!list_empty(&entry->e_lru_list)) {
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list_del_init(&entry->e_lru_list);
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cache->c_entry_count--;
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atomic_dec(&entry->e_refcnt);
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}
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spin_unlock(&cache->c_lru_list_lock);
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mb2_cache_entry_put(cache, entry);
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return;
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}
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}
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hlist_bl_unlock(head);
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}
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EXPORT_SYMBOL(mb2_cache_entry_delete_block);
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/* mb2_cache_entry_touch - cache entry got used
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* @cache - cache the entry belongs to
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* @entry - entry that got used
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*
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* Move entry in lru list to reflect the fact that it was used.
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*/
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void mb2_cache_entry_touch(struct mb2_cache *cache,
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struct mb2_cache_entry *entry)
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{
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spin_lock(&cache->c_lru_list_lock);
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if (!list_empty(&entry->e_lru_list))
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list_move_tail(&cache->c_lru_list, &entry->e_lru_list);
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spin_unlock(&cache->c_lru_list_lock);
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}
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EXPORT_SYMBOL(mb2_cache_entry_touch);
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static unsigned long mb2_cache_count(struct shrinker *shrink,
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struct shrink_control *sc)
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{
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struct mb2_cache *cache = container_of(shrink, struct mb2_cache,
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c_shrink);
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return cache->c_entry_count;
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}
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/* Shrink number of entries in cache */
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static unsigned long mb2_cache_scan(struct shrinker *shrink,
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struct shrink_control *sc)
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{
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int nr_to_scan = sc->nr_to_scan;
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struct mb2_cache *cache = container_of(shrink, struct mb2_cache,
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c_shrink);
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struct mb2_cache_entry *entry;
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struct hlist_bl_head *head;
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unsigned int shrunk = 0;
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spin_lock(&cache->c_lru_list_lock);
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while (nr_to_scan-- && !list_empty(&cache->c_lru_list)) {
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entry = list_first_entry(&cache->c_lru_list,
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struct mb2_cache_entry, e_lru_list);
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list_del_init(&entry->e_lru_list);
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cache->c_entry_count--;
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/*
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* We keep LRU list reference so that entry doesn't go away
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* from under us.
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*/
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spin_unlock(&cache->c_lru_list_lock);
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head = entry->e_hash_list_head;
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hlist_bl_lock(head);
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if (!hlist_bl_unhashed(&entry->e_hash_list)) {
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hlist_bl_del_init(&entry->e_hash_list);
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atomic_dec(&entry->e_refcnt);
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}
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hlist_bl_unlock(head);
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if (mb2_cache_entry_put(cache, entry))
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shrunk++;
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cond_resched();
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spin_lock(&cache->c_lru_list_lock);
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}
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spin_unlock(&cache->c_lru_list_lock);
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return shrunk;
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}
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/*
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* mb2_cache_create - create cache
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* @bucket_bits: log2 of the hash table size
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*
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* Create cache for keys with 2^bucket_bits hash entries.
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*/
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struct mb2_cache *mb2_cache_create(int bucket_bits)
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{
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struct mb2_cache *cache;
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int bucket_count = 1 << bucket_bits;
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int i;
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if (!try_module_get(THIS_MODULE))
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return NULL;
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cache = kzalloc(sizeof(struct mb2_cache), GFP_KERNEL);
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if (!cache)
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goto err_out;
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cache->c_bucket_bits = bucket_bits;
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INIT_LIST_HEAD(&cache->c_lru_list);
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spin_lock_init(&cache->c_lru_list_lock);
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cache->c_hash = kmalloc(bucket_count * sizeof(struct hlist_bl_head),
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GFP_KERNEL);
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if (!cache->c_hash) {
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kfree(cache);
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goto err_out;
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}
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for (i = 0; i < bucket_count; i++)
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INIT_HLIST_BL_HEAD(&cache->c_hash[i]);
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cache->c_shrink.count_objects = mb2_cache_count;
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cache->c_shrink.scan_objects = mb2_cache_scan;
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cache->c_shrink.seeks = DEFAULT_SEEKS;
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register_shrinker(&cache->c_shrink);
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return cache;
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err_out:
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module_put(THIS_MODULE);
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return NULL;
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}
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EXPORT_SYMBOL(mb2_cache_create);
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/*
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* mb2_cache_destroy - destroy cache
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* @cache: the cache to destroy
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*
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* Free all entries in cache and cache itself. Caller must make sure nobody
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* (except shrinker) can reach @cache when calling this.
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*/
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void mb2_cache_destroy(struct mb2_cache *cache)
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{
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struct mb2_cache_entry *entry, *next;
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unregister_shrinker(&cache->c_shrink);
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/*
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* We don't bother with any locking. Cache must not be used at this
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* point.
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*/
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list_for_each_entry_safe(entry, next, &cache->c_lru_list, e_lru_list) {
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if (!hlist_bl_unhashed(&entry->e_hash_list)) {
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hlist_bl_del_init(&entry->e_hash_list);
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atomic_dec(&entry->e_refcnt);
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} else
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WARN_ON(1);
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list_del(&entry->e_lru_list);
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WARN_ON(atomic_read(&entry->e_refcnt) != 1);
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mb2_cache_entry_put(cache, entry);
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}
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kfree(cache->c_hash);
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kfree(cache);
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module_put(THIS_MODULE);
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}
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EXPORT_SYMBOL(mb2_cache_destroy);
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static int __init mb2cache_init(void)
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{
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mb2_entry_cache = kmem_cache_create("mbcache",
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sizeof(struct mb2_cache_entry), 0,
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SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD, NULL);
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BUG_ON(!mb2_entry_cache);
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return 0;
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}
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static void __exit mb2cache_exit(void)
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{
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kmem_cache_destroy(mb2_entry_cache);
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}
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module_init(mb2cache_init)
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module_exit(mb2cache_exit)
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MODULE_AUTHOR("Jan Kara <jack@suse.cz>");
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MODULE_DESCRIPTION("Meta block cache (for extended attributes)");
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MODULE_LICENSE("GPL");
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