linux-kernel - Re: [PATCH v3 14/16] Gut bio_add

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Message-ID: <20120529020815.GB5091@dastard>
Date:	Tue, 29 May 2012 12:08:15 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Mikulas Patocka <mpatocka@...hat.com>,
	Alasdair G Kergon <agk@...hat.com>,
	Kent Overstreet <koverstreet@...gle.com>,
	Mike Snitzer <snitzer@...hat.com>,
	linux-kernel@...r.kernel.org, linux-bcache@...r.kernel.org,
	dm-devel@...hat.com, linux-fsdevel@...r.kernel.org,
	axboe@...nel.dk, yehuda@...newdream.net, vgoyal@...hat.com,
	bharrosh@...asas.com, sage@...dream.net, drbd-dev@...ts.linbit.com,
	Dave Chinner <dchinner@...hat.com>, tytso@...gle.com,
	"Martin K. Petersen" <martin.petersen@...cle.com>
Subject: Re: [PATCH v3 14/16] Gut bio_add_page()

On Tue, May 29, 2012 at 08:02:08AM +0900, Tejun Heo wrote:
> (cc'ing Martin K. Petersen, hi!)
> 
> On Tue, May 29, 2012 at 06:38:39AM +0900, Tejun Heo wrote:
> > > With this patchset, you don't have to expose all the limits. You can 
> > > expose just a few most useful limits to avoid bio split in the cases 
> > > described above.
> > 
> > Yeah, if that actually helps, sure.  From what I read, dm is already
> > (ab)using merge_bvec_fn() like that anyway.
> 
> i thought a bit more about it and the only thing which makes sense to
> me is exposing the stripe granularity for striped devices -
> ie. something which says "if you go across this boundary, the
> performance characteristics including latency might get affected",
> which should fit nicely with the rest of topology information.
> Martin, adding that shouldn't be difficult, right?

We already have the optimal IO size/alignment field in the topology.
Doesn't this fit what you want exactly?

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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