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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
struct mb_cache {
struct list_head c_cache_list;
const char *c_name;
struct mb_cache_op c_op;
atomic_t c_entry_count;
int c_bucket_bits;
#ifndef MB_CACHE_INDEXES_COUNT
int c_indexes_count;
#endif
struct kmem_cache *c_entry_cache;
struct list_head *c_block_hash;
struct list_head *c_indexes_hash[0];
};
/*
* 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);
static inline int
mb_cache_indexes(struct mb_cache *cache)
{
#ifdef MB_CACHE_INDEXES_COUNT
return MB_CACHE_INDEXES_COUNT;
#else
return cache->c_indexes_count;
#endif
}
/*
* What the mbcache registers as to get shrunk dynamically.
*/
static int mb_cache_shrink_fn(struct shrinker *shrink, int nr_to_scan, gfp_t gfp_mask);
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)
{
int n;
if (__mb_cache_entry_is_hashed(ce)) {
list_del_init(&ce->e_block_list);
for (n=0; n<mb_cache_indexes(ce->e_cache); n++)
list_del(&ce->e_indexes[n].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));
if (cache->c_op.free && cache->c_op.free(ce, gfp_mask)) {
/* free failed -- put back on the lru list
for freeing later. */
spin_lock(&mb_cache_spinlock);
list_add(&ce->e_lru_list, &mb_cache_lru_list);
spin_unlock(&mb_cache_spinlock);
} else {
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)
* @nr_to_scan: Number of objects to scan
* @gfp_mask: (ignored)
*
* Returns the number of objects which are present in the cache.
*/
static int
mb_cache_shrink_fn(struct shrinker *shrink, int nr_to_scan, gfp_t gfp_mask)
{
LIST_HEAD(free_list);
struct list_head *l, *ltmp;
int count = 0;
spin_lock(&mb_cache_spinlock);
list_for_each(l, &mb_cache_list) {
struct mb_cache *cache =
list_entry(l, struct mb_cache, c_cache_list);
mb_debug("cache %s (%d)", cache->c_name,
atomic_read(&cache->c_entry_count));
count += atomic_read(&cache->c_entry_count);
}
mb_debug("trying to free %d entries", nr_to_scan);
if (nr_to_scan == 0) {
spin_unlock(&mb_cache_spinlock);
goto out;
}
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);
}
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_mask);
}
out:
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)
* @cache_op: contains the callback called when freeing a cache entry
* @entry_size: The size of a cache entry, including
* struct mb_cache_entry
* @indexes_count: number of additional indexes in the cache. Must equal
* MB_CACHE_INDEXES_COUNT if the number of indexes is
* hardwired.
* @bucket_bits: log2(number of hash buckets)
*/
struct mb_cache *
mb_cache_create(const char *name, struct mb_cache_op *cache_op,
size_t entry_size, int indexes_count, int bucket_bits)
{
int m=0, n, bucket_count = 1 << bucket_bits;
struct mb_cache *cache = NULL;
if(entry_size < sizeof(struct mb_cache_entry) +
indexes_count * sizeof(((struct mb_cache_entry *) 0)->e_indexes[0]))
return NULL;
cache = kmalloc(sizeof(struct mb_cache) +
indexes_count * sizeof(struct list_head), GFP_KERNEL);
if (!cache)
goto fail;
cache->c_name
|