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.
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@xxxxxxx>
---
fs/mbcache2.c | 41 +++++++++++++++++++++++++++++++++--------
include/linux/mbcache2.h | 7 +++++--
2 files changed, 38 insertions(+), 10 deletions(-)
diff --git a/fs/mbcache2.c b/fs/mbcache2.c
index fe9f6f6a2953..60310a690f8d 100644
--- a/fs/mbcache2.c
+++ b/fs/mbcache2.c
@@ -39,6 +39,29 @@ 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
@@ -83,7 +106,7 @@ struct mb2_cache_entry *mb2_cache_entry_create(struct mb2_cache *cache,
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) {
@@ -125,7 +148,7 @@ EXPORT_SYMBOL(__mb2_cache_entry_free);
void mb2_cache_entry_delete(struct mb2_cache *cache,
struct mb2_cache_entry *entry)
{
- struct hlist_bl_head *head = entry->e_hash_list_head;
+ struct hlist_bl_head *head = mb2_cache_entry_head(entry);
hlist_bl_lock(head);
if (!hlist_bl_unhashed(&entry->e_hash_list)) {
@@ -153,7 +176,7 @@ 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);
@@ -256,10 +279,7 @@ EXPORT_SYMBOL(mb2_cache_entry_delete_block);
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);
@@ -284,6 +304,11 @@ static unsigned long mb2_cache_shrink(struct mb2_cache *cache,
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);
+ if (mb2_cache_entry_referenced(entry)) {
+ mb2_cache_entry_clear_referenced(entry);
+ list_move_tail(&cache->c_lru_list, &entry->e_lru_list);
+ continue;
+ }
list_del_init(&entry->e_lru_list);
cache->c_entry_count--;
/*
@@ -291,7 +316,7 @@ static unsigned long mb2_cache_shrink(struct mb2_cache *cache,
* from under us.
*/
spin_unlock(&cache->c_lru_list_lock);
- head = entry->e_hash_list_head;
+ 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);
diff --git a/include/linux/mbcache2.h b/include/linux/mbcache2.h
index 2a58c51c3a0a..ca5b509c14a8 100644
--- a/include/linux/mbcache2.h
+++ b/include/linux/mbcache2.h
@@ -19,8 +19,11 @@ struct mb2_cache_entry {
unsigned int 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);
--
2.1.4
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