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#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_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 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 */
int 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 int 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
* @block - block that contains data
* @reusable - is the block reusable by other inodes?
*
* 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 mb_cache_entry_create(struct mb_cache *cache, gfp_t mask, u32 key,
sector_t block, 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);
/* One ref for hash, one ref returned */
atomic_set(&entry->e_refcnt, 1);
entry->e_key = key;
entry->e_block = block;
entry->e_reusable = reusable;
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_block == block) {
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);
/* Grab ref for LRU list */
atomic_inc(&entry->e_refcnt);
cache->c_entry_count++;
spin_unlock(&cache->c_list_lock);
return 0;
}
EXPORT_SYMBOL(mb_cache_entry_create);
void __mb_cache_entry_free(struct mb_cache_entry *entry)
{
kmem_cache_free(mb_entry_cache, entry);
}
EXPORT_SYMBOL(__mb_cache_entry_free);
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 && entry->e_reusable) {
atomic_inc(&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 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 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 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 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 block number (and key)
* @cache - cache we work with
* @key - key of block number @block
* @block - block number
*/
struct mb_cache_entry *mb_cache_entry_get(struct mb_cache *cache, u32 key,
sector_t block)
{
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_block == block) {
atomic_inc(&entry->e_refcnt);
goto out;
}
}
entry = NULL;
out:
hlist_bl_unlock(head);
return entry;
}
EXPORT_SYMBOL(mb_cache_entry_get);
/* mb_cache_entry_delete_block - remove information about block from cache
* @cache - cache we work with
* @key - key of block @block
* @block - block number
*
* Remove entry from cache @cache with key @key with data stored in @block.
*/
void mb_cache_entry_delete_block(struct mb_cache *cache, u32 key,
sector_t block)
{
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_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_list_lock);
if (!list_empty(&entry->e_list)) {
list_del_init(&entry->e_list);
cache->c_entry_count--;
atomic_dec(&entry->e_refcnt);
}
spin_unlock(&cache->c_list_lock);
mb_cache_entry_put(cache, entry);
return;
}
}
hlist_bl_unlock(head);
}
EXPORT_SYMBOL(mb_cache_entry_delete_block);
/* 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)
{
entry->e_referenced = 1;
}
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 int nr_to_scan)
{
struct mb_cache_entry *entry;
struct hlist_bl_head *head;
unsigned int 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);
if (entry->e_referenced) {
entry->e_referenced = 0;
list_move_tail(&cache->c_list, &entry->e_list);
continue;
}
list_del_init(&
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