#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/mbcache2.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
* mb2_cache_entry_delete_block()).
*
* Ext2 and ext4 use this cache for deduplication of extended attribute blocks.
* They use hash of a block contents as a key and block number as a value.
* That's why keys need not be unique (different xattr blocks may end up having
* the same hash). However block number 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 mb2_cache {
/* Hash table of entries */
struct hlist_bl_head *c_hash;
/* log2 of hash table size */
int c_bucket_bits;
/* Protects c_lru_list, c_entry_count */
spinlock_t c_lru_list_lock;
struct list_head c_lru_list;
/* Number of entries in cache */
unsigned long c_entry_count;
struct shrinker c_shrink;
};
static struct kmem_cache *mb2_entry_cache;
/*
* mb2_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
* @block - block that contains data
*
* Creates entry in @cache with key @key and records that data is stored in
* block @block. The function returns -EBUSY if entry with the same key
* and for the same block already exists in cache. Otherwise 0 is returned.
*/
int mb2_cache_entry_create(struct mb2_cache *cache, gfp_t mask, u32 key,
sector_t block)
{
struct mb2_cache_entry *entry, *dup;
struct hlist_bl_node *dup_node;
struct hlist_bl_head *head;
entry = kmem_cache_alloc(mb2_entry_cache, mask);
if (!entry)
return -ENOMEM;
INIT_LIST_HEAD(&entry->e_lru_list);
/* One ref for hash, one ref returned */
atomic_set(&entry->e_refcnt, 1);
entry->e_key = key;
entry->e_block = block;
head = &cache->c_hash[hash_32(key, cache->c_bucket_bits)];
entry->e_hash_list_head = head;
hlist_bl_lock(head);
hlist_bl_for_each_entry(dup, dup_node, head, e_hash_list) {
if (dup->e_key == key && dup->e_block == block) {
hlist_bl_unlock(head);
kmem_cache_free(mb2_entry_cache, entry);
return -EBUSY;
}
}
hlist_bl_add_head(&entry->e_hash_list, head);
hlist_bl_unlock(head);
spin_lock(&cache->c_lru_list_lock);
list_add_tail(&entry->e_lru_list, &cache->c_lru_list);
/* Grab ref for LRU list */
atomic_inc(&entry->e_refcnt);
cache->c_entry_count++;
spin_unlock(&cache->c_lru_list_lock);
return 0;
}
EXPORT_SYMBOL(mb2_cache_entry_create);
void __mb2_cache_entry_free(struct mb2_cache_entry *entry)
{
kmem_cache_free(mb2_entry_cache, entry);
}
EXPORT_SYMBOL(__mb2_cache_entry_free);
static struct mb2_cache_entry *__entry_find(struct mb2_cache *cache,
struct mb2_cache_entry *entry,
u32 key)
{
struct mb2_cache_entry *old_entry = entry;
struct hlist_bl_node *node;
struct hlist_bl_head *head;
if (entry)
head = entry->e_hash_list_head;
else
head = &cache->c_hash[hash_32(key, cache->c_bucket_bits)];
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 mb2_cache_entry,
e_hash_list);
if (entry->e_key == key) {
atomic_inc(&entry->e_refcnt);
goto out;
}
node = node->next;
}
entry = NULL;
out:
hlist_bl_unlock(head);
if (old_entry)
mb2_cache_entry_put(cache, old_entry);
return entry;
}
/*
* mb2_cache_entry_find_first - find the first entry in cache with given key
* @cache: cache where we should search
* @key: key to look for
*
* Search in @cache for entry with key @key. Grabs reference to the first
* entry found and returns the entry.
*/
struct mb2_cache_entry *mb2_cache_entry_find_first(struct mb2_cache *cache,
u32 key)
{
return __entry_find(cache, NULL, key);
}
EXPORT_SYMBOL(mb2_cache_entry_find_first);
/*
* mb2_cache_entry_find_next - find next entry in cache with the same
* @cache: cache where we should search
* @entry: entry to start search from
*
* Finds next 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 entry in the hash chain. The function
* drops reference to @entry and returns with a reference to the found entry.
*/
struct mb2_cache_entry *mb2_cache_entry_find_next(struct mb2_cache *cache,
struct mb2_cache_entry *entry)
{
return __entry_find(cache, entry, entry->e_key);
}
EXPORT_SYMBOL(mb2_cache_entry_find_next);
/* mb2_cache_entry_delete_block - remove information about block from cache
* @cache - cache we work with
* @key - key of the entry to remove
* @block - block containing data for @key
*
* Remove entry from cache @cache with key @key with data stored in @block.
*/
void mb2_cache_entry_delete_block(struct mb2_cache *cache, u32 key,
sector_t block)
{
struct hlist_bl_node *node;
struct hlist_bl_head *head;
struct mb2_cache_entry *entry;
head = &cache->c_hash[hash_32(key, cache->c_bucket_bits)];
hlist_bl_lock(head);
hlist_bl_for_each_entry(entry, node, head, e_hash_list) {
if (entry->e_key == key && entry->e_block == block) {
/* We keep hash list reference to keep entry alive */
hlist_bl_del_init(&entry->e_hash_list);
hlist_bl_unlock(head);
spin_lock(&cache->c_lru_list_lock);
if (!list_empty(&entry->e_lru_list)) {
list_del_init(&entry->e_lru_list);
cache->c_entry_count--;
atomic_dec(&entry->e_refcnt);
}
spin_unlock(&cache->c_lru_list_lock);
mb2_cache_entry_put(cache, entry);
return;
}
}
hlist_bl_unlock(head);
}
EXPORT_SYMBOL(mb2_cache_entry_delete_block);
/* mb2_cache_entry_touch - cache entry got used
* @cache - cache the entry belongs to
* @entry - entry that got used
*
* Move entry in lru list to reflect the fact that it was used.
*/
void mb2_cache_entry_touch(struct mb2_cache *cache,
struct mb2_cache_entry *entry)
{
spin_lock(&cache->c_lru_list_lock);
if (!list_empty(&entry->e_lru_list))
list_move_tail(&cache->c_lru_list, &entry->e_lru_list);
spin_unlock(&cache->c_lru_list_lock);
}
EXPORT_SYMBOL(mb2_cache_entry_touch);
static unsigned long mb2_cache_count(struct shrinker *shrink,
struct shrink_control *sc)
{
struct mb2_cache *cache = container_of(shrink, struct mb2_cache,
c_shrink);
return cache->c_entry_count;
}
/* Shrink number of entries in cache */
static unsigned long mb2_cache_scan(struct shrinker *shrink,
struct shrink_control *sc)
{
int nr_to_scan = sc->nr_to_scan;
struct mb2_cache *cache = container_of(shrink, struct mb2_cache,
c_shrink);
struct mb2_cache_entry *entry;
struct hlist_bl_head *head;
unsigned int shrunk = 0;
spin_lock(&cache->c_lru_list_lock);
while (nr_to_scan-- && !list_empty(&cache->c_lru_list)) {
entry = list_first_entry(&cache->c_lru_list,
struct mb2_cache_entry, e_lru_list);
list_del_init(&entry->e_lru_list);
cache->c_entry_count--;
/*
* We keep LRU list reference so that entry doesn't go away
* from under us.
*/
spin_unlock(&cache->c_lru_list_lock);
head = entry->e_hash_list_head;
hlist_bl_lock(head);
if (!hlist_bl_unhashed(&entry->e_hash_list)) {
hlist_bl_del_init(&entry->e_hash_list);
atomic_dec(&entry->e_refcnt);
}
hlist_bl_unlock(head);
if (mb2_cache_entry_put(cache, entry))
shrunk++;
cond_resched();
spin_lock(&cache->c_lru_list_lock);
}
spin_unlock(&cache->c_lru_list_lock);
return shrunk;
}
/*
* mb2_cache_create - create cache
* @bucket_bits: log2 of the hash table size
*
* Create cache for keys with 2^bucket_bits hash entries.
*/
struct mb2_cache *mb2_cache_create(int bucket_bits)
{
struct mb2_cache *cache;
int bucket_count = 1 << bucket_bits;
int i;
if (!try_module_get(THIS_MODULE))
return NULL;
cache = kzalloc(sizeof(struct mb2_cache), GFP_KERNEL);
if (!cache)
goto err_out;
cache->c_bucket_bits = bucket_bits;
INIT_LIST_HEAD(&cache->c_lru_list);
spin_lock_init(&cache->c_lru_list_lock);
cache->c_hash = kmalloc(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 = mb2_cache_count;
cache->c_shrink.scan_objects = mb2_cache_scan;
cache->c_shrink.seeks = DEFAULT_SEEKS;
register_shrinker(&cache->c_shrink);
return cache;
err_out:
module_put(THIS_MODULE);
return NULL;
}
EXPORT_SYMBOL(mb2_cache_create);
/*
* mb2_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 mb2_cache_destroy(struct mb2_cache *cache)
{
struct mb2_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_lru_list, e_lru_list) {
if (!hlist_bl_unhashed(&entry->e_hash_list)) {
hlist_bl_del_init(&entry->e_hash_list);
atomic_dec(&entry->e_refcnt);
} else
WARN_ON(1);
list_del(&entry->e_lru_list);
WARN_ON(atomic_read(&entry->e_refcnt) != 1);
mb2_cache_entry_put(cache, entry);
}
kfree(cache->c_hash);
kfree(cache);
module_put(THIS_MODULE);
}
EXPORT_SYMBOL(mb2_cache_destroy);
static int __init mb2cache_init(void)
{
mb2_entry_cache = kmem_cache_create("mbcache",
sizeof(struct mb2_cache_entry), 0,
SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD, NULL);
BUG_ON(!mb2_entry_cache);
return 0;
}
static void __exit mb2cache_exit(void)
{
kmem_cache_destroy(mb2_entry_cache);
}
module_init(mb2cache_init)
module_exit(mb2cache_exit)
MODULE_AUTHOR("Jan Kara <jack@suse.cz>");
MODULE_DESCRIPTION("Meta block cache (for extended attributes)");
MODULE_LICENSE("GPL");
