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From: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Subject: Re: [PATCHSET v3.1 0/7] data integrity: Stabilize pages during writeback for various fses
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Date: Wed, 11 May 2011 01:12:13 +0900
In-Reply-To: <20110510145421.GJ4402@quack.suse.cz> (Jan Kara's message of
	"Tue, 10 May 2011 16:54:21 +0200")
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To: Jan Kara <jack@suse.cz>
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>

Jan Kara <jack@suse.cz> writes:

>> 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, that was considered as well. We'd have to essentially migrate the
> page that is under writeback and should be written to. You are going to pay
> the cost of page allocation, copy, increased memory & cache pressure.
> Depending on your backing storage and workload this may or may not be better
> than waiting for IO...

Maybe possible, but you really think on usual case just blocking is
better?

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

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