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