From: Jan Kara <jack@suse.cz>
Subject: Re: [PATCHSET v3.1 0/7] data integrity: Stabilize pages during
 writeback for various fses
Date: Thu, 12 May 2011 11:42:55 +0200
Message-ID: <20110512094255.GA4690@quack.suse.cz>
References: <20110509230318.19566.66202.stgit@elm3c44.beaverton.ibm.com>
 <20110510125124.GD4402@quack.suse.cz>
 <20110511181901.GK20579@tux1.beaverton.ibm.com>
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Cc: Jan Kara <jack@suse.cz>, Theodore Tso <tytso@mit.edu>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>,
	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: "Darrick J. Wong" <djwong@us.ibm.com>
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On Wed 11-05-11 11:19:01, Darrick J. Wong wrote:
> On Tue, May 10, 2011 at 02:51:24PM +0200, Jan Kara wrote:
> > On Mon 09-05-11 16:03:18, Darrick J. Wong wrote:
> > > I am still chasing down what exactly is broken in ext3.  data=writeback mode
> > > passes with no failures.  data=ordered, however, does not pass; my current
> > > suspicion is that jbd is calling submit_bh on data buffers but doesn't call
> > > page_mkclean to kick the userspace programs off the page before writing it.
> >   Yes, ext3 in data=ordered mode writes pages from
> > journal_commit_transaction() via submit_bh() without clearing page dirty
> > bits thus page_mkclean() is not called for these pages. Frankly, do you
> > really want to bother with adding support for ext2 and ext3? People can use
> > ext4 as a fs driver when they want to start using blk-integrity support.
> > Especially ext2 patch looks really painful and just from a quick look I can
> > see code e.g. in fs/ext2/namei.c which isn't handled by your patch yet.
> 
> Yeah, I agree that ext2 is ugly and ext3/jbd might be more painful.  Are there
> any other code that wants stable pages that's already running with ext3?  In
> this months-long discussion I've heard that encryption and raid also like
> stable pages during writes.  Have those users been broken this whole time, or
> have they been stabilizing pages themselves?
  I believe part of them has been broken (e.g. raid) and part of them do
copy-out so they were OK.

> I suppose we can cross the "ext3 fails horribly on DIF" bridge when someone
> complains about it.  Possibly we could try to steer them to btrfs.
  Well, btrfs might be a bit too advantageous for production servers but
ext4 would be definitely viable for them.

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

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