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Date: Thu, 22 Nov 2007 13:06:11 +0100
From: Andi Kleen <andi@firstfloor.org>
Subject: Re: [PATCH 2/9]: Reduce Log I/O latency
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References: <20071122003339.GH114266761__34694.2978365861$1195691722$gmane$org@sgi.com> <p73oddnhzoq.fsf@bingen.suse.de> <20071122011214.GR114266761@sgi.com> <1195702123.8369.78.camel@localhost.localdomain>
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To: Stewart Smith <stewart@mysql.com>
Cc: David Chinner <dgc@sgi.com>, Andi Kleen <andi@firstfloor.org>, xfs-oss <xfs@oss.sgi.com>, lkml <linux-kernel@vger.kernel.org>

> FWIW from a "real time" database POV this seems to make sense to me...
> in fact, we probably rely on filesystem metadata way too much
> (historically it's just "worked".... although we do seem to get issues
> on ext3).

For that case you really would need priority inheritance: any metadata
IO on behalf or blocking a process needs to use the process' block IO 
priority.

David's change just fixes a limited set of cases, but breaks others.

-Andi