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: Wed, 11 May 2011 00:24:58 +0900
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References: <20110509230318.19566.66202.stgit@elm3c44.beaverton.ibm.com>
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Cc: Christoph Hellwig <hch@infradead.org>,
	"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>, 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>
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Jan Kara <jack@suse.cz> writes:

>> Isn't it reallocated blocks too, and metadata too?
>   Reallocated blocks - not really. For a block to be freed it cannot be
> under writeback and when it's freed no writeback is started.

Sure for data -> data reallocated case. metadata -> data/metadata is
still there.

> For metadata - yes. But ext3, ext4, xfs, btrfs have to avoid modifying
> metadata under writeback anyway (because of journalling / COW
> constraints) and thus they don't care.

Yes. Those would use better way than just blocking.

> For ext2 or vfat it's a different story. But as I wrote to Darrick,
> I'm not sure about vfat but for ext2 and similar legacy filesystems,
> I'd rather let them live with their unstable pages under IO ;) because
> I see a limited use for that.

If this patches was not going to tackle it, I have no argument here ;)
It would be simply FS specific approach/fixes anymore like journal.

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