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/*
* 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.
*/
#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/init.h>
#include <linux/mbcache.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)
static DECLARE_WAIT_QUEUE_HEAD(mb_cache_queue);
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);
/*
* What the mbcache registers as to get shrunk dynamically.
*/
static int mb_cache_shrink_fn(struct shrinker *shrink,
struct shrink_control *sc);
static struct shrinker mb_cache_shrinker = {
.shrink = mb_cache_shrink_fn,
.seeks = DEFAULT_SEEKS,
};
static inline int
__mb_cache_entry_is_hashed(struct mb_cache_entry *ce)
{
return !list_empty(&ce->e_block_list);
}
static void
__mb_cache_entry_unhash(struct mb_cache_entry *ce)
{
if (__mb_cache_entry_is_hashed(ce)) {
list_del_init(&ce->e_block_list);
list_del(&ce->e_index.o_list);
}
}
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));
kmem_cache_free(cache->c_entry_cache, ce);
atomic_dec(&cache->c_entry_count);
}
static void
__mb_cache_entry_release_unlock(struct mb_cache_entry *ce)
__releases(mb_cache_spinlock)
{
/* 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;
ce->e_used--;
if (!(ce->e_used || ce->e_queued)) {
if (!__mb_cache_entry_is_hashed(ce))
goto forget;
mb_assert(list_empty(&ce->e_lru_list));
list_add_tail(&ce->e_lru_list, &mb_cache_lru_list);
}
spin_unlock(&mb_cache_spinlock);
return;
forget:
spin_unlock(&mb_cache_spinlock);
__mb_cache_entry_forget(ce, GFP_KERNEL);
}
/*
* mb_cache_shrink_fn() 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 which are present in the cache.
*/
static int
mb_cache_shrink_fn(struct shrinker *shrink, struct shrink_control *sc)
{
LIST_HEAD(free_list);
struct mb_cache *cache;
struct mb_cache_entry *entry, *tmp;
int count = 0;
int nr_to_scan = sc->nr_to_scan;
gfp_t gfp_mask = sc->gfp_mask;
mb_debug("trying to free %d entries", nr_to_scan);
spin_lock(&mb_cache_spinlock);
while (nr_to_scan-- && !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_move_tail(&ce->e_lru_list, &free_list);
__mb_cache_entry_unhash(ce);
}
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);
list_for_each_entry_safe(entry, tmp, &free_list, e_lru_list) {
__mb_cache_entry_forget(entry, gfp_mask);
}
return (count / 100) * sysctl_vfs_cache_pressure;
}
/*
* 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;
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 list_head),
GFP_KERNEL);
if (!cache->c_block_hash)
goto fail;
for (n=0; n<bucket_count; n++)
INIT_LIST_HEAD(&cache->c_block_hash[n]);
cache->c_index_hash = kmalloc(bucket_count * sizeof(struct list_head),
GFP_KERNEL);
if (!cache->c_index_hash)
goto fail;
for (n=0; n<bucket_count; n++)
INIT_LIST_HEAD(&cache->c_index_hash[n]);
cache->c_entry_cache = kmem_cache_create(name,
sizeof(struct mb_cache_entry), 0,
SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD, NULL);
if (!cache->c_entry_cache)
goto fail2;
/*
* 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, *ltmp;
spin_lock(&mb_cache_spinlock);
list_for_each_safe(l, ltmp, &mb_cache_lru_list) {
struct mb_cache_entry *ce =
list_entry(l, struct mb_cache_entry, e_lru_list);
if (ce->e_bdev == bdev) {
list_move_tail(&ce->e_lru_list, &free_list);
__mb_cache_entry_unhash(ce);
}
}
spin_unlock(&mb_cache_spinlock);
list_for_each_safe(l, ltmp, &free_list) {
__mb_cache_entry_forget(list_entry(l, struct mb_cache_entry,
e_lru_list), 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 list_head *l, *ltmp;
spin_lock(&mb_cache_spinlock);
list_for_each_safe(l, ltmp, &mb_cache_lru_list) {
struct mb_cache_entry *ce =
list_entry(l, struct mb_cache_entry, e_lru_list);
if (ce->e_cache == cache) {
list_move_tail(&ce->e_lru_list, &free_list);
__mb_cache_entry_unhash(ce);
}
}
list_del(&cache->c_cache_list);
spin_unlock(&mb_cache_spinlock);
list_for_each_safe(l, ltmp, &free_list) {
__mb_cache_entry_forget(list_entry(l, struct mb_cache_entry,
e_lru_list), 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));
}
kmem_cache_destroy(cache->c_entry_cache);
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 = NULL;
if (atomic_read(&cache->c_entry_count) >= cache->c_max_entries) {
spin_lock(&mb_cache_spinlock);
if (!list_empty(&mb_cache_lru_list)) {
ce = list_entry(mb_cache_lru_list.next,
struct mb_cache_entry, e_lru_list);
list_del_init(&ce->e_lru_list);
__mb_cache_entry_unhash(ce);
}
spin_unlock(&mb_cache_spinlock);
}
if (!ce) {
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_LIST_HEAD(&ce->e_block_list);
ce->e_cache = cache;
ce->e_queued = 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 list_head *l;
int error = -EBUSY;
bucket = hash_long((unsigned long)bdev + (block & 0xffffffff),
cache->c_bucket_bits);
spin_lock(&mb_cache_spinlock);
list_for_each_prev(l, &cache->c_block_hash[bucket]) {
struct mb_cache_entry *ce =
list_entry(l, struct mb_cache_entry, e_block_list);
if (ce->e_bdev == bdev && ce->e_block == block)
goto out;
}
__mb_cache_entry_unhash(ce);
ce->e_bdev = bdev;
ce->e_block = block;
list_add(&ce->e_block_list, &cache->c_block_hash[bucket]);
ce->e_index.o_key = key;
bucket = hash_long(key, cache->c_bucket_bits);
list_add(&ce->e_index.o_list, &cache->c_index_hash[bucket]);
error = 0;
out:
spin_unlock(&mb_cache_spinlock);
return error;
}
/*
* 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)
{
spin_lock(&mb_cache_spinlock);
__mb_cache_entry_release_unlock(ce);
}
/*
* mb_cache_entry_free()
*
* This is equivalent to the sequence mb_cache_entry_takeout() --
* mb_cache_entry_release().
*/
void
mb_cache_entry_free(struct mb_cache_entry *ce)
{
spin_lock(&mb_cache_spinlock);
mb_assert(list_empty(&ce->e_lru_list));
__mb_cache_entry_unhash(ce);
__mb_cache_entry_release_unlock(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 list_head *l;
struct mb_cache_entry *ce;
bucket = hash_long((unsigned long)bdev + (block & 0xffffffff),
cache->c_bucket_bits);
spin_lock(&mb_cache_spinlock);
list_for_each(l, &cache->c_block_hash[bucket]) {
ce = list_entry(l, struct mb_cache_entry, e_block_list);
if (ce->e_bdev == bdev && ce->e_block == block) {
DEFINE_WAIT(wait);
if (!list_empty(&ce->e_lru_list))
list_del_init(&ce->e_lru_list);
while (ce->e_used > 0) {
ce->e_queued++;
prepare_to_wait(&mb_cache_queue, &wait,
TASK_UNINTERRUPTIBLE);
spin_unlock(&mb_cache_spinlock);
schedule();
spin_lock(&mb_cache_spinlock);
ce->e_queued--;
}
finish_wait(&mb_cache_queue, &wait);
ce->e_used += 1 + MB_CACHE_WRITER;
if (!__mb_cache_entry_is_hashed(ce)) {
__mb_cache_entry_release_unlock(ce);
return NULL;
}
goto cleanup;
}
}
ce = NULL;
cleanup:
spin_unlock(&mb_cache_spinlock);
return ce;
}
#if !defined(MB_CACHE_INDEXES_COUNT) || (MB_CACHE_INDEXES_COUNT > 0)
static struct mb_cache_entry *
__mb_cache_entry_find(struct list_head *l, struct list_head *head,
struct block_device *bdev, unsigned int key)
{
while (l != head) {
struct mb_cache_entry *ce =
list_entry(l, struct mb_cache_entry, e_index.o_list);
if (ce->e_bdev == bdev && ce->e_index.o_key == key) {
DEFINE_WAIT(wait);
if (!list_empty(&ce->e_lru_list))
list_del_init(&ce->e_lru_list);
/* Incrementing before holding the lock gives readers
priority over writers. */
ce->e_used++;
while (ce->e_used >= MB_CACHE_WRITER) {
ce->e_queued++;
prepare_to_wait(&mb_cache_queue, &wait,
TASK_UNINTERRUPTIBLE);
spin_unlock(&mb_cache_spinlock);
schedule();
spin_lock(&mb_cache_spinlock);
ce->e_queued--;
}
finish_wait(&mb_cache_queue, &wait);
if (!__mb_cache_entry_is_hashed(ce)) {
__mb_cache_entry_release_unlock(ce);
spin_lock(&mb_cache_spinlock);
return ERR_PTR(-EAGAIN);
}
return ce;
}
l = l->next;
}
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 list_head *l;
struct mb_cache_entry *ce;
spin_lock(&mb_cache_spinlock);
l = cache->c_index_hash[bucket].next;
ce = __mb_cache_entry_find(l, &cache->c_index_hash[bucket], bdev, key);
spin_unlock(&mb_cache_spinlock);
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 list_head *l;
struct mb_cache_entry *ce;
spin_lock(&mb_cache_spinlock);
l = prev->e_index.o_list.next;
ce = __mb_cache_entry_find(l, &cache->c_index_hash[bucket], bdev, key);
__mb_cache_entry_release_unlock(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)
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