linux-kernel - Re: Wrong DIF guard tag on ext2 write

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Message-ID: <yq1hblmkgka.fsf@sermon.lab.mkp.net>
Date:	Tue, 01 Jun 2010 09:50:29 -0400
From:	"Martin K. Petersen" <martin.petersen@...cle.com>
To:	James Bottomley <James.Bottomley@...e.de>
Cc:	Chris Mason <chris.mason@...cle.com>,
	Christof Schmitt <christof.schmitt@...ibm.com>,
	Boaz Harrosh <bharrosh@...asas.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: Wrong DIF guard tag on ext2 write

>>>>> "James" == James Bottomley <James.Bottomley@...e.de> writes:

James> Would it be too much work in the fs to mark the page dirty before
James> you begin altering it (and again after you finish, just in case
James> some cleaner noticed and initiated a write)?  Or some other flag
James> that indicates page under modification?  All the process
James> controlling the writeout (which is pretty high up in the stack)
James> needs to know is if we triggered the check error by altering the
James> page while it was in flight.

James> I agree that a block based retry would close all the holes ... it
James> just doesn't look elegant to me that the fs will already be
James> repeating the I/O if it changed the page and so will block.

I experimented with this approach a while back.  However, I quickly got
into a situation where frequently updated blocks never made it to disk
because the page was constantly being updated.  And all writes failed
with a guard tag error.

-- 
Martin K. Petersen	Oracle Linux Engineering
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