Re: [PATCH] Allow increasing the buffer-head per-CPU LRU size
From: Sebastien Buisson
Date: Mon Jul 07 2014 - 06:32:21 EST
Allow increasing 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 accesses 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 can be changed at config time, and its
default value is raised to 16.
Signed-off-by: Liang Zhen <liang.zhen@xxxxxxxxx>
Signed-off-by: Andreas Dilger <andreas.dilger@xxxxxxxxx>
---
fs/Kconfig | 9 +++++++++
fs/buffer.c | 3 +--
2 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/fs/Kconfig b/fs/Kconfig
index c229f82..c08844c 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -268,4 +268,13 @@ endif # NETWORK_FILESYSTEMS
source "fs/nls/Kconfig"
source "fs/dlm/Kconfig"
+config BH_LRU_SIZE
+ int
+ range 8 64
+ default "16"
+ help
+ This sets the per-CPU LRU size for buffer heads in memory.
+ More complex filesystems may be modifying multiple blocks
+ within a single transaction, so keeping the buffer heads in
+ CPU-local cache speeds up modifications significantly.
endmenu
diff --git a/fs/buffer.c b/fs/buffer.c
index 6024877..b83fa63 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1255,8 +1255,7 @@ static struct buffer_head *__bread_slow(struct
buffer_head *bh)
* The LRUs themselves only need locking against invalidate_bh_lrus.
We use
* a local interrupt disable for that.
*/
-
-#define BH_LRU_SIZE 8
+#define BH_LRU_SIZE CONFIG_BH_LRU_SIZE
struct bh_lru {
struct buffer_head *bhs[BH_LRU_SIZE];
--
1.7.1
Le 06/07/2014 18:18, Andi Kleen a écrit :
Sebastien Buisson <sebastien.buisson@xxxxxxxx> writes:
Allow increasing 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 accesses multiple buffer heads and will overflow the LRU
at the default 8-block LRU size:
I don't think that should be a user visible config. Most users wouldn't
know how to set it. And Linux already has far too many obscure
config options.
Either make it set implicitely by the file system config.
Or just increase it unconditionally?
-Andi
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