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SubjectRe: ext2 write performance regression from 2.6.32
On Wed 16-02-11 17:40:31, Feng Tang wrote:
> Hi,
>
> I made out a debug patch which try to delay the pure FS metadata writeback
> (maxim 30 seconds to match current writeback expire time). It works for me
> on 2.6.32, and the dd performance is restored.
>
> Please help to review it, thanks!
>
> btw, I've sent out the block dump info requested by Jan Kara, but didn't see
> it on LKML, so attached them again.
>
> - Feng
>
> From c35548c7d0c3a334d24c26adab277ef62b9825db Mon Sep 17 00:00:00 2001
> From: Feng Tang <feng.tang@intel.com>
> Date: Wed, 16 Feb 2011 17:27:36 +0800
> Subject: [PATCH] writeback: delay the file system metadata writeback in 30 seconds
>
> Signed-off-by: Feng Tang <feng.tang@intel.com>
> ---
> fs/fs-writeback.c | 10 ++++++++++
> 1 files changed, 10 insertions(+), 0 deletions(-)
>
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 9d5360c..418fd9e 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -635,6 +635,16 @@ static void writeback_inodes_wb(struct bdi_writeback *wb,
> continue;
> }
>
> + if ((wbc->sync_mode != WB_SYNC_ALL)
> + && !inode->i_ino
> + && !strcmp(inode->i_sb->s_id, "bdev")) {
> + if (inode->dirtied_when + 30 * HZ > jiffies) {
> + list_move(&inode->i_list, &wb->b_dirty);
> + continue;
> + }
> + }
> +
> +
Doh, this is a crude hack! Nice for debugging but no way to get this into
the kernel. We have to find a cleaner way to speedup the writeback...

Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR


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