From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sebastien Buisson Subject: Re: [PATCH] Allow increasing the buffer-head per-CPU LRU size Date: Mon, 7 Jul 2014 12:32:12 +0200 Message-ID: <53BA772C.6040506@bull.net> References: <53B667F9.90306@bull.net> <87y4w6sbp7.fsf@tassilo.jf.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: , , , Andrew Morton To: Andi Kleen Return-path: In-Reply-To: <87y4w6sbp7.fsf@tassilo.jf.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org Allow increasing the buffer-head per-CPU LRU size to allow efficient filesystem operations that access many blocks for each transaction. =46or 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 Signed-off-by: Andreas Dilger --- 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=20 buffer_head *bh) * The LRUs themselves only need locking against invalidate_bh_lrus.=20 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]; --=20 1.7.1 Le 06/07/2014 18:18, Andi Kleen a =E9crit : > Sebastien Buisson 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 LR= U >> 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 > >