linux-ext4 - Re: [patch,rfc v2] ext3/4: enhance fsync performance when using cfq

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Message-ID: <20100408140653.GP10103@kernel.dk>
Date:	Thu, 8 Apr 2010 16:06:53 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>, Theodore Ts'o <tytso@....edu>,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch,rfc v2] ext3/4: enhance fsync performance when using cfq

On Thu, Apr 08 2010, Jeff Moyer wrote:
> Vivek Goyal <vgoyal@...hat.com> writes:
> 
> > On Thu, Apr 08, 2010 at 01:00:45PM +0200, Jens Axboe wrote:
> 
> >> I like the concept, it's definitely useful (and your results amply
> >> demonstrate that). I was thinking if there was a way in through the ioc
> >> itself, rather than bdi -> queue and like you are doing. But I can't
> >> think of a nice way to do it, so this is probably as good as it gets.
> >> 
> >
> > I think, one issue with ioc based approach will be that it will then call
> > yield operation on all the devices in the system where this context has ever
> > done any IO. With bdi based approach this call will remain limited to
> > a smaller set of devices.
> 
> Which actually brings up the question of whether this needs some
> knowledge of whether the journal is on the same device as the file
> system!  In such a case, we need not yield.  I think I'll stick my head
> in the sand for this one.  ;-)

Yes, that is true. But that should be relatively easy to check.

-- 
Jens Axboe

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