linux-kernel - Re: [patch 1/1] Writeback fix for concurrent large and small file writes

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Date:	Tue, 4 Dec 2007 01:06:06 -0800
From:	"Michael Rubin" <mrubin@...gle.com>
To:	"Fengguang Wu" <wfg@...l.ustc.edu.cn>
Cc:	a.p.zijlstra@...llo.nl, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	"Chris Mason" <chris.mason@...cle.com>
Subject: Re: [patch 1/1] Writeback fix for concurrent large and small file writes

On Nov 29, 2007 5:32 PM, Fengguang Wu <wfg@...l.ustc.edu.cnwrote:
> > On Nov 28, 2007 4:34 PM, Fengguang Wu <wfg@...l.ustc.edu.cn> wrote:
> > > Could you demonstrate the situation? Or if I guess it right, could it
> > > be fixed by the following patch?

Feng I am sorry to have been mistaken but I reran my tests and I am
now finding that the patch you gave me is NOT fixing the problem.  The
patch I refer to is the one you posted on this thread that adds a
requeue_io in __sync_single_inode.

I tarred up my test code. It is still in very rough shape but it can
reproduce the issue. You can find it here:

http://neverthere.org/mhr/wb/wb-test.tar.bz2

Just make the test and run it with the args "-duration 0:5:0
-starvation". You must be root so it can set some sysctl values.

> One major concern could be whether a continuous writer dirting pages
> at the 'right' pace will generate a steady flow of write I/Os which are
> _tiny_hence_inefficient_.
>
> So it's not a problem in *theory* :-)
>
> > I will post this change for 2.6.24 and list Feng as author. If that's
> > ok with Feng.

I am going to try to track down what is up in 2.6.24 and see if I can
find a less dramatic fix than my tree patch for the short term. If you
get a chance to reproduce the problem with my test on your patch that
would rock.

I still would like to see my full patch accepted into 2.6.25. A patch
should be arriving shortly that will incorporate my larger patch and
Qi Yong's fix for skip-writing-data-pages-when-inode-is-under-i_sync.
http://www.gossamer-threads.com/lists/linux/kernel/849493

As always thanks for your patience,

mrubin
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