From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Martin K. Petersen" <martin.petersen@oracle.com>
Subject: Re: Wrong DIF guard tag on ext2 write
Date: Tue, 01 Jun 2010 09:50:29 -0400
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Cc: Chris Mason <chris.mason@oracle.com>,
	Christof Schmitt <christof.schmitt@de.ibm.com>,
	Boaz Harrosh <bharrosh@panasas.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
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To: James Bottomley <James.Bottomley@suse.de>
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>>>>> "James" == James Bottomley <James.Bottomley@suse.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