linux-kernel - Re: [LFS/VM TOPIC] Stable pages while IO (was Wrong DIF guard tag on ext2 write)

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Date:	Fri, 4 Jun 2010 18:23:32 +0200
From:	Jan Kara <jack@...e.cz>
To:	Boaz Harrosh <bharrosh@...asas.com>
Cc:	Christof Schmitt <christof.schmitt@...ibm.com>,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, lsf10-pc@...ts.linuxfoundation.org,
	Nick Piggin <npiggin@...e.de>,
	Al Viro <viro@...IV.linux.org.uk>,
	Chris Mason <chris.mason@...cle.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Ric Wheeler <rwheeler@...hat.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Vladislav Bolkhovitin <vst@...b.net>,
	Christoph Hellwig <hch@....de>
Subject: Re: [LFS/VM TOPIC] Stable pages while IO (was Wrong DIF guard tag
 on ext2 write)

On Thu 03-06-10 19:09:52, Boaz Harrosh wrote:
> [Topic]
> How to not let pages change while in IO
> 
> [Abstract]
> As seen in a long thread on the fsdvel scsi mailing lists. Lots of
> people have headaches and sleep less nights because individual pages
> can change while in IO and/or DMA. Though each one as slightly different
> needs, the mechanics look to be the same.
  Hmm, I don't think it's really about "how to not let pages change" - that
is doable by using wait_on_page_writeback() in ->page_mkwrite and
->write_begin. I think the discussion is more about whether we should do it
or whether we should rechecksum and resubmit IO in case of checksum failure
as Nick proposed...

								Honza
> People that care:
> - Mirror and RAID people that need on disk consistency.
> - Network storage that wants data checksum.
> - DIF/DIX people
> - ...
> 
> I for one know nothing of the subject but am a RAID person and would
> like a solution that does not force me to copy the complete data load.
> 
> Please lets get all the VM VFS and drivers people in one room and see
> if we can have a Linux solution to this problem
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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