linux-ext4 - Re: [PATCHSET v3.1 0/7] data integrity: Stabilize pages during writeback for various fses

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Date:	Mon, 16 May 2011 20:59:47 +0200
From:	Jan Kara <jack@...e.cz>
To:	"Darrick J. Wong" <djwong@...ibm.com>
Cc:	Jan Kara <jack@...e.cz>, Theodore Tso <tytso@....edu>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	Jens Axboe <axboe@...nel.dk>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Jeff Layton <jlayton@...hat.com>,
	Dave Chinner <david@...morbit.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Christoph Hellwig <hch@...radead.org>, linux-mm@...ck.org,
	Chris Mason <chris.mason@...cle.com>,
	Joel Becker <jlbec@...lplan.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-ext4@...r.kernel.org, Mingming Cao <mcao@...ibm.com>
Subject: Re: [PATCHSET v3.1 0/7] data integrity: Stabilize pages during
 writeback for various fses

On Mon 16-05-11 11:49:27, Darrick J. Wong wrote:
> On Thu, May 12, 2011 at 11:42:55AM +0200, Jan Kara wrote:
> > 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.
> 
> A future step might be to undo all these homegrown copy-outs?
  Sure but I'm not the right one to tell you where these are ;).

> > > 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.
> 
> Are there any distros that are going straight from ext3 to btrfs?
  Most distros currently offer users a choice of xfs, ext3, ext4, btrfs
with ext4 being the default. I'm not sure if that's what you are asking
about...

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