linux-kernel - Re: [PATCHSET block#for-2.6.36-post] block: replace barrier with sequenced flush

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Date:	Wed, 18 Aug 2010 10:11:22 +0200
From:	Tejun Heo <teheo@...e.de>
To:	Christoph Hellwig <hch@....de>
Cc:	jaxboe@...ionio.com, linux-fsdevel@...r.kernel.org,
	linux-scsi@...r.kernel.org, linux-ide@...r.kernel.org,
	linux-kernel@...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, jack@...e.cz,
	rwheeler@...hat.com, hare@...e.de
Subject: Re: [PATCHSET block#for-2.6.36-post] block: replace barrier with
 sequenced flush

Hello,

On 08/18/2010 08:35 AM, Tejun Heo wrote:
>> It's not bisecting to find bugs in the barrier conversion.  We can't
>> easily bisect it down anyway.  The problem is when we try to bisect
>> other problems and get into the middle of the series barriers suddenly
>> are gone.  Which is not very helpful for things like data integrity
>> problems in filesystems.
> 
> Ah, okay, hmmm.... alright, I'll resequence the patches.  If the
> filesystem changes can be put into a single tree somehow, we can keep
> things mostly working at least for direct devices.

Sorry but I'm doing it.  It just doesn't make much sense.  I can't
relax the ordering for REQ_HARDBARRIER without breaking the remapping
drivers.  So, to keep things working, I'll have to 1. relax the
ordering 2. implement new REQ_FLUSH/FUA based interface and 3. use
them in the filesystems in the same patch.  That's just wrong.  And I
don't think md/dm changes can or should go through the block tree.
They're way too invasive for that.  It's a new implementation and
barrier won't work (fail gracefully) for several commits during the
transition.  I don't think there's a better way around it.

Thanks.

-- 
tejun
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