From: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Subject: Re: [PATCHSET v3.1 0/7] data integrity: Stabilize pages during writeback for various fses
Date: Tue, 10 May 2011 23:05:41 +0900
Message-ID: <87zkmu3b2i.fsf@devron.myhome.or.jp>
References: <20110509230318.19566.66202.stgit@elm3c44.beaverton.ibm.com>
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	<20110510123819.GB4402@quack.suse.cz>
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	<20110510132953.GE4402@quack.suse.cz>
	<878vue4qjb.fsf@devron.myhome.or.jp>
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Cc: "Darrick J. Wong" <djwong@us.ibm.com>,
	Theodore Tso <tytso@mit.edu>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Jens Axboe <axboe@kernel.dk>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	Jeff Layton <jlayton@redhat.com>,
	Dave Chinner <david@fromorbit.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Dave Hansen <dave@linux.vnet.ibm.com>,
	Christoph Hellwig <hch@infradead.org>, linux-mm@kvack.org,
	Chris Mason <chris.mason@oracle.com>,
	Joel Becker <jlbec@evilplan.org>,
	linux-scsi <linux-scsi@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	linux-ext4@vger.kernel.org, Mingming Cao <mcao@us.ibm.com>
To: Jan Kara <jack@suse.cz>
In-Reply-To: <878vue4qjb.fsf@devron.myhome.or.jp> (OGAWA Hirofumi's message of
	"Tue, 10 May 2011 22:46:16 +0900")
Sender: linux-ext4-owner@vger.kernel.org

OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> writes:

> Jan Kara <jack@suse.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.

missed question mark in here.

Did you already consider, 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.
-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>