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

From:		Jan Kara <jack-AT-suse.cz>
To:		OGAWA Hirofumi <hirofumi-AT-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 18:22:37 +0200
Message-ID:		<20110510162237.GM4402@quack.suse.cz>
Cc:		Jan Kara <jack-AT-suse.cz>, "Darrick J. Wong" <djwong-AT-us.ibm.com>, Theodore Tso <tytso-AT-mit.edu>, Alexander Viro <viro-AT-zeniv.linux.org.uk>, Jens Axboe <axboe-AT-kernel.dk>, "Martin K. Petersen" <martin.petersen-AT-oracle.com>, Jeff Layton <jlayton-AT-redhat.com>, Dave Chinner <david-AT-fromorbit.com>, linux-kernel <linux-kernel-AT-vger.kernel.org>, Dave Hansen <dave-AT-linux.vnet.ibm.com>, Christoph Hellwig <hch-AT-infradead.org>, linux-mm-AT-kvack.org, Chris Mason <chris.mason-AT-oracle.com>, Joel Becker <jlbec-AT-evilplan.org>, linux-scsi <linux-scsi-AT-vger.kernel.org>, linux-fsdevel <linux-fsdevel-AT-vger.kernel.org>, linux-ext4-AT-vger.kernel.org, Mingming Cao <mcao-AT-us.ibm.com>
Archive-link:		Article, Thread

On Wed 11-05-11 01:12:13, OGAWA Hirofumi wrote:
> 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?
  Define usual case... As Christoph noted, we don't currently have a real
practical case where blocking would matter (since frequent rewrites are
rather rare). So defining what is usual when we don't have a single real
case is kind of tough ;)

								Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR

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