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Date: Mon, 7 Jul 2014 12:32:12 +0200
From: Sebastien Buisson <sebastien.buisson@...l.net>
To: Andi Kleen <andi@...stfloor.org>
CC: <viro@...iv.linux.org.uk>, <linux-fsdevel@...r.kernel.org>,
<linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] Allow increasing the buffer-head per-CPU LRU size
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@...el.com>
Signed-off-by: Andreas Dilger <andreas.dilger@...el.com>
---
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@...l.net> 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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