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mbcache2: Use referenced bit instead of LRU

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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
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11
include/linux/mbcache2.h
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@@ -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);