[PATCH] Increase the buffer-head per-CPU LRU size

[Sebastien Buisson]

Increase the buffer-head per-CPU LRU size to allow efficient
filesystem operations that access many blocks for each transaction.
For example, creating a file in a large ext4 directory with quota
enabled will access multiple buffer heads and will overflow the LRU
at the default 8-block LRU size:

* parent directory inode table block (ctime, nlinks for subdirs)
* new inode bitmap
* inode table block
* 2 quota blocks
* directory leaf block (not reused, but pollutes one cache entry)
* 2 levels htree blocks (only one is reused, other pollutes cache)
* 2 levels indirect/index blocks (only one is reused)

The buffer-head per-CPU LRU size is raised to 16, as it shows in
metadata performance benchmarks up to 10% gain for create,
4% for lookup and 7% for destroy.

Signed-off-by: Liang Zhen <liang.zhen@xxxxxxxxx>
Signed-off-by: Andreas Dilger <andreas.dilger@xxxxxxxxx>
Signed-off-by: Sebastien Buisson <sebastien.buisson@xxxxxxxx>
---
 fs/buffer.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 6024877..a6468f2 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1256,7 +1256,7 @@ static struct buffer_head *__bread_slow(struct buffer_head *bh)
  * a local interrupt disable for that.
  */
 
-#define BH_LRU_SIZE	8
+#define BH_LRU_SIZE	16
 
 struct bh_lru {
 	struct buffer_head *bhs[BH_LRU_SIZE];
-- 
1.7.1

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