linux-kernel - Re: writeout stalls in current -git

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Date:	Tue, 6 Nov 2007 21:26:05 +0100
From:	"Torsten Kaiser" <just.for.lkml@...glemail.com>
To:	"Peter Zijlstra" <peterz@...radead.org>
Cc:	"David Chinner" <dgc@....com>,
	"Fengguang Wu" <wfg@...l.ustc.edu.cn>,
	"Maxim Levitsky" <maximlevitsky@...il.com>,
	linux-kernel@...r.kernel.org,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, xfs@....sgi.com
Subject: Re: writeout stalls in current -git

On 11/6/07, Peter Zijlstra <peterz@...radead.org> wrote:
> On Tue, 2007-11-06 at 15:25 +1100, David Chinner wrote:
>
> > I'm struggling to understand what possible changed in XFS or writeback that
> > would lead to stalls like this, esp. as you appear to be removing files when
> > the stalls occur.
>
> Just a crazy idea,..
>
> Could there be a set_page_dirty() that doesn't have
> balance_dirty_pages() call near? For example modifying meta data in
> unlink?
>
> Such a situation could lead to an excess of dirty pages and the next
> call to balance_dirty_pages() would appear to stall, as it would
> desperately try to get below the limit again.

Only if accounting of the dirty pages is also broken.
In the unmerge testcase I see most of the time only <200kb of dirty
data in /proc/meminfo.

The system has 4Gb of RAM so I'm not sure if it should ever be valid
to stall even the emerge/install testcase.

Torsten

Now building a kernel with the skipped-pages-accounting-patch reverted...
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