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

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Message-ID: <20110511181901.GK20579@tux1.beaverton.ibm.com>
Date:	Wed, 11 May 2011 11:19:01 -0700
From:	"Darrick J. Wong" <djwong@...ibm.com>
To:	Jan Kara <jack@...e.cz>
Cc:	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 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 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.

--D
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