linux-kernel - Re: [PATCH 26/30] ext4: do not send discards as barriers

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Date:	Fri, 27 Aug 2010 19:31:48 +0200
From:	Jan Kara <jack@...e.cz>
To:	Tejun Heo <tj@...nel.org>
Cc:	Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@....de>,
	jaxboe@...ionio.com, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-ide@...r.kernel.org, linux-raid@...r.kernel.org,
	James.Bottomley@...e.de, tytso@....edu, chris.mason@...cle.com,
	swhiteho@...hat.com, konishi.ryusuke@....ntt.co.jp,
	dm-devel@...hat.com, vst@...b.net, rwheeler@...hat.com,
	hare@...e.de, neilb@...e.de, rusty@...tcorp.com.au, mst@...hat.com,
	jeremy@...p.org, snitzer@...hat.com, k-ueda@...jp.nec.com,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH 26/30] ext4: do not send discards as barriers

On Thu 26-08-10 10:25:47, Tejun Heo wrote:
> On 08/25/2010 10:02 PM, Jan Kara wrote:
> > On Wed 25-08-10 17:57:41, Tejun Heo wrote:
> >> On 08/25/2010 06:00 PM, Christoph Hellwig wrote:
> >>> On Wed, Aug 25, 2010 at 05:58:42PM +0200, Christoph Hellwig wrote:
> >>>> On Wed, Aug 25, 2010 at 05:47:43PM +0200, Tejun Heo wrote:
> >>>>> From: Christoph Hellwig <hch@...radead.org>
> >>>>>
> >>>>> ext4 already uses synchronous discards, no need to add I/O barriers.
> >>>>
> >>>> This needs the patch that Jan sent in reply to my initial version merged
> >>>> into it.
> >>>
> >>> Actually the jbd2 patch needs it merged, but the point still stands.
> >>
> >> Yeah, wasn't sure about that one.  Has anyone tested it?  I'll be
> >> happy to merge it but I have no idea whether it's correct or not and
> >> Jan didn't seem to have tested it so...  Jan, shall I merge the patch?
> >   I'm quite confident the patch is correct so you can merge it I think but
> > tomorrow I'll give it some crash testing together with the rest of your
> > patch set in KVM to be sure.
> 
> Patch included in the series before jbd2 conversion patch.
  An update: I've set up an ext4 barrier testing in KVM - run fsstress,
kill KVM at some random moment and check that the filesystem is consistent
(kvm is run in cache=writeback mode to simulate disk cache). About 70 runs
without journal_async_commit passed fine, now I'm running some tests with
the option enabled and the first few rounds passed OK as well.

									Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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