From: Jan Kara <jack@suse.cz>
Subject: Re: [PATCHSET v3.1 0/7] data integrity: Stabilize pages during
 writeback for various fses
Date: Tue, 10 May 2011 16:49:39 +0200
Message-ID: <20110510144939.GI4402@quack.suse.cz>
References: <20110509230318.19566.66202.stgit@elm3c44.beaverton.ibm.com>
 <87tyd31fkc.fsf@devron.myhome.or.jp>
 <20110510133603.GA5823@infradead.org>
 <874o524q9h.fsf@devron.myhome.or.jp>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: Christoph Hellwig <hch@infradead.org>,
	"Darrick J. Wong" <djwong@us.ibm.com>, Theodore Tso <tytso@mit.edu>,
	Jan Kara <jack@suse.cz>, 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: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Return-path: <owner-linux-mm@kvack.org>
Content-Disposition: inline
In-Reply-To: <874o524q9h.fsf@devron.myhome.or.jp>
Sender: owner-linux-mm@kvack.org
List-Id: linux-ext4.vger.kernel.org

On Tue 10-05-11 22:52:10, OGAWA Hirofumi wrote:
> Christoph Hellwig <hch@infradead.org> writes:
> 
> > On Tue, May 10, 2011 at 10:59:15AM +0900, OGAWA Hirofumi wrote:
> >> I'd like to know those patches are on what state. Waiting in writeback
> >> page makes slower, like you mentioned it (I guess it would more
> >> noticeable if device was slower that like FAT uses). And I think
> >> currently it doesn't help anything others for blk-integrity stuff
> >> (without other technic, it doesn't help FS consistency)?
> >
> > It only makes things slower if we rewrite a region in a file that is
> > currently undergoing writeback. I'd be interested to know about real
> > life applications doing that, and if they really are badly affect we
> > should help them to work around that in userspace, e.g. by adding a
> > fadvice will rewrite call that might be used to never write back that
> > regions without an explicit fsync call.
> 
> 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. 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. 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.

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

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>