linux-kernel - Re: [PATCH 0/7] writeback: avoid touching dirtied

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Date:	Sat, 22 Oct 2011 15:07:35 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Jan Kara <jack@...e.cz>
Cc:	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Dave Chinner <david@...morbit.com>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Tang, Feng" <feng.tang@...el.com>
Subject: Re: [PATCH 0/7] writeback: avoid touching dirtied_when on blocked
 inodes

On Sat, Oct 22, 2011 at 02:59:26PM +0800, Wu Fengguang wrote:
> > In general it looks better we first root case the "decreasing wrote
> > pages by writeback_single_inode() over time" problem before looking
> > into further steps..
> 
> The problem shows up in many of the regression cases. For example,
> the thresh=1G/ext4-100dd case with patches 1-4 applied will not only
> see nr_writeback occasionally dropped low (bdi_dirty_state-8:0.png),
> but also see repeated pattern of nr_wrote by writeback_single_inode()
> slowly decreasing to 0 during some period of dozens of seconds
> (writeback_single_inode.png).

Another example is the thresh=1G/xfs-100dd case with patches 1-4 and
Jan's requeue_io_wait-on-I_SYNC patch. The writeback_single_inode.png
graph shows steadily decreasing wrote pages in some period of 400
seconds. It's accompanied by decrease of nr_writeback, IO size and
impacts write bandwidth a lot.

Thanks,
Fengguang

Download attachment "bdi_dirty_state-8:0.png" of type "image/png" (54418 bytes)

Download attachment "writeback_single_inode.png" of type "image/png" (46406 bytes)

Download attachment "iostat-misc.png" of type "image/png" (43585 bytes)

Download attachment "iostat-bw.png" of type "image/png" (65248 bytes)