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From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [Lsf] IO less throttling and cgroup aware writeback (Was: Re:
 Preliminary Agenda and Activities for LSF)
Date: Fri, 1 Apr 2011 02:32:54 -0400
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Cc: Vivek Goyal <vgoyal@redhat.com>,
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To: Dave Chinner <david@fromorbit.com>
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On Fri, Apr 01, 2011 at 03:36:05PM +1100, Dave Chinner wrote:
> > If that's a concern,
> > can filesystem mark that bio (REQ_META?) and throttling logic can possibly
> > let these bio pass through.
> 
> We already tag most metadata IO in this way.

Actually we don't tag any I/O that way right now.  That's mostly
because REQ_META assumes it's synchronous I/O and cfg and the block
layer give id additional priority, while in XFS metadata writes
are mostly asynchronous.  We'll need a properly defined REQ_META
to use it, which currently is not the case.