linux-kernel - Re: Linux 2.6.29

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Date:	Tue, 24 Mar 2009 09:15:45 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	David Rees <drees76@...il.com>
Cc:	Jesper Krogh <jesper@...gh.cc>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 2.6.29

> posted to the list earlier trying to see if there was anything that
> could be done to help my specific case.  I've got a system where if
> someone starts writing out a large file, it kills client NFS writes.
> Makes the system unusable:
> http://marc.info/?l=linux-kernel&m=123732127919368&w=2

I have not had this problem since I applied Arjan's (for some reason
repeatedly rejected) patch to change the ioprio of the various writeback
daemons. Under some loads changing to the noop I/O scheduler also seems
to help (as do most of the non default ones)

> Everyone seems to agree that "autotuning" it is the way to go.  But no
> one seems willing to step up and try to do it.  Probably because it's
> hard to get right!

If this is a VM problem why does fixing the I/O priority of the various
daemons seem to cure at least some of it ?

Alan
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