linux-ext4 - Re: [PATCHSET v3.1 0/7] data integrity: Stabilize pages during writeback for various fses

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Date:	Tue, 10 May 2011 22:46:16 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Jan Kara <jack@...e.cz>
Cc:	"Darrick J. Wong" <djwong@...ibm.com>,
	Theodore Tso <tytso@....edu>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Jens Axboe <axboe@...nel.dk>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Jeff Layton <jlayton@...hat.com>,
	Dave Chinner <david@...morbit.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Christoph Hellwig <hch@...radead.org>, linux-mm@...ck.org,
	Chris Mason <chris.mason@...cle.com>,
	Joel Becker <jlbec@...lplan.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-ext4@...r.kernel.org, Mingming Cao <mcao@...ibm.com>
Subject: Re: [PATCHSET v3.1 0/7] data integrity: Stabilize pages during writeback for various fses

Jan Kara <jack@...e.cz> writes:

>> I see. So many block layer stuff sounds like broken on corner case? If
>> so, I more feel this approach should be temporary workaround, and should
>> use another less-blocking approach.
>   Not many but some... The alternative to less blocking approach is to do
> copy-out before a page is submitted for IO (or various middle ground
> alternatives of doing sometimes copyout, sometimes blocking...). That costs
> some performance as well. We talked about it at LSF and the approach
> Darrick is implementing was considered the least intrusive. There's really
> no way to fix these corner cases and keep performance.

You already considered, to copy only if page was writeback (like
copy-on-write). I.e. if page is on I/O, copy, then switch the page for
writing new data.

Yes, it is complex. But I think blocking and overhead is minimum, and
this can be used as infrastructure for copy-on-write FS.

Thanks.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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