FEX-Emu/linux
1
0
Fork 0
mirror of https://github.com/FEX-Emu/linux.git synced 2024-12-22 09:22:37 +00:00
Code Issues Actions Packages Projects Releases Wiki Activity

mbcache2: Use referenced bit instead of LRU

Browse Source 
Currently we maintain perfect LRU list by moving entry to the tail of
the list when it gets used. However these operations on cache-global
list are relatively expensive.

In this patch we switch to lazy updates of LRU list. Whenever entry gets
used, we set a referenced bit in it. When reclaiming entries, we give
referenced entries another round in the LRU. Since the list is not a
real LRU anymore, rename it to just 'list'.

In my testing this logic gives about 30% boost to workloads with mostly
unique xattr blocks (e.g. xattr-bench with 10 files and 10000 unique
xattr values).

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Jan Kara 2016-02-22 18:23:47 -05:00 committed by Theodore Ts'o
parent c2f3140fe2
commit f0c8b46238
2 changed files with 63 additions and 35 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

87
fs/mbcache2.c
View File

@ -30,9 +30,9 @@ struct mb2_cache {
int c_bucket_bits;
/* Maximum entries in cache to avoid degrading hash too much */
int c_max_entries;
/* Protects c_lru_list, c_entry_count */
spinlock_t c_lru_list_lock;
struct list_head c_lru_list;
/* 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;
@ -45,6 +45,29 @@ static struct kmem_cache *mb2_entry_cache;
static unsigned long mb2_cache_shrink(struct mb2_cache *cache,
unsigned int nr_to_scan);
static inline bool mb2_cache_entry_referenced(struct mb2_cache_entry *entry)
{
return entry->_e_hash_list_head & 1;
}
static inline void mb2_cache_entry_set_referenced(struct mb2_cache_entry *entry)
{
entry->_e_hash_list_head |= 1;
}
static inline void mb2_cache_entry_clear_referenced(
struct mb2_cache_entry *entry)
{
entry->_e_hash_list_head &= ~1;
}
static inline struct hlist_bl_head *mb2_cache_entry_head(
struct mb2_cache_entry *entry)
{
return (struct hlist_bl_head *)
(entry->_e_hash_list_head & ~1);
}
/*
* Number of entries to reclaim synchronously when there are too many entries
* in cache
@ -80,13 +103,13 @@ int mb2_cache_entry_create(struct mb2_cache *cache, gfp_t mask, u32 key,
if (!entry)
return -ENOMEM;
INIT_LIST_HEAD(&entry->e_lru_list);
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;
head = &cache->c_hash[hash_32(key, cache->c_bucket_bits)];
entry->e_hash_list_head = head;
entry->_e_hash_list_head = (unsigned long)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) {
@ -98,12 +121,12 @@ int mb2_cache_entry_create(struct mb2_cache *cache, gfp_t mask, u32 key,
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);
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_lru_list_lock);
spin_unlock(&cache->c_list_lock);
return 0;
}
@ -124,7 +147,7 @@ static struct mb2_cache_entry *__entry_find(struct mb2_cache *cache,
struct hlist_bl_head *head;
if (entry)
head = entry->e_hash_list_head;
head = mb2_cache_entry_head(entry);
else
head = &cache->c_hash[hash_32(key, cache->c_bucket_bits)];
hlist_bl_lock(head);
@ -203,13 +226,13 @@ void mb2_cache_entry_delete_block(struct mb2_cache *cache, u32 key,
/* 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);
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_lru_list_lock);
spin_unlock(&cache->c_list_lock);
mb2_cache_entry_put(cache, entry);
return;
}
@ -222,15 +245,12 @@ EXPORT_SYMBOL(mb2_cache_entry_delete_block);
* @cache - cache the entry belongs to
* @entry - entry that got used
*
* Move entry in lru list to reflect the fact that it was used.
* Marks entry as used to give hit higher chances of surviving in cache.
*/
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);
mb2_cache_entry_set_referenced(entry);
}
EXPORT_SYMBOL(mb2_cache_entry_touch);
@ -251,18 +271,23 @@ static unsigned long mb2_cache_shrink(struct mb2_cache *cache,
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);
spin_lock(&cache->c_list_lock);
while (nr_to_scan-- && !list_empty(&cache->c_list)) {
entry = list_first_entry(&cache->c_list,
struct mb2_cache_entry, e_list);
if (mb2_cache_entry_referenced(entry)) {
mb2_cache_entry_clear_referenced(entry);
list_move_tail(&cache->c_list, &entry->e_list);
continue;
}
list_del_init(&entry->e_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;
spin_unlock(&cache->c_list_lock);
head = mb2_cache_entry_head(entry);
hlist_bl_lock(head);
if (!hlist_bl_unhashed(&entry->e_hash_list)) {
hlist_bl_del_init(&entry->e_hash_list);
@ -272,9 +297,9 @@ static unsigned long mb2_cache_shrink(struct mb2_cache *cache,
if (mb2_cache_entry_put(cache, entry))
shrunk++;
cond_resched();
spin_lock(&cache->c_lru_list_lock);
spin_lock(&cache->c_list_lock);
}
spin_unlock(&cache->c_lru_list_lock);
spin_unlock(&cache->c_list_lock);
return shrunk;
}
@ -318,8 +343,8 @@ struct mb2_cache *mb2_cache_create(int bucket_bits)
goto err_out;
cache->c_bucket_bits = bucket_bits;
cache->c_max_entries = bucket_count << 4;
INIT_LIST_HEAD(&cache->c_lru_list);
spin_lock_init(&cache->c_lru_list_lock);
INIT_LIST_HEAD(&cache->c_list);
spin_lock_init(&cache->c_list_lock);
cache->c_hash = kmalloc(bucket_count * sizeof(struct hlist_bl_head),
GFP_KERNEL);
if (!cache->c_hash) {
@ -361,13 +386,13 @@ void mb2_cache_destroy(struct mb2_cache *cache)
* 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) {
list_for_each_entry_safe(entry, next, &cache->c_list, e_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);
list_del(&entry->e_list);
WARN_ON(atomic_read(&entry->e_refcnt) != 1);
mb2_cache_entry_put(cache, entry);
}

11
include/linux/mbcache2.h
View File

@ -10,8 +10,8 @@
struct mb2_cache;
struct mb2_cache_entry {
/* LRU list - protected by cache->c_lru_list_lock */
struct list_head e_lru_list;
/* List of entries in cache - protected by cache->c_list_lock */
struct list_head e_list;
/* Hash table list - protected by bitlock in e_hash_list_head */
struct hlist_bl_node e_hash_list;
atomic_t e_refcnt;
@ -19,8 +19,11 @@ struct mb2_cache_entry {
u32 e_key;
/* Block number of hashed block - stable during lifetime of the entry */
sector_t e_block;
/* Head of hash list (for list bit lock) - stable */
struct hlist_bl_head *e_hash_list_head;
/*
* Head of hash list (for list bit lock) - stable. Combined with
* referenced bit of entry
*/
unsigned long _e_hash_list_head;
};
struct mb2_cache *mb2_cache_create(int bucket_bits);