linux-ext4 - Re: REGRESSION: [PATCH 04/12] ext4: Disable merging of uninitialized extents

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Date:	Thu, 14 Feb 2013 11:47:34 +0100
From:	Jan Kara <jack@...e.cz>
To:	Dmitry Monakhov <dmonakhov@...nvz.org>
Cc:	Theodore Ts'o <tytso@....edu>, Jan Kara <jack@...e.cz>,
	linux-ext4@...r.kernel.org
Subject: Re: REGRESSION: [PATCH 04/12] ext4: Disable merging of
 uninitialized extents

On Wed 13-02-13 11:26:40, Dmitry Monakhov wrote:
> On Tue, 12 Feb 2013 23:57:59 -0500, Theodore Ts'o <tytso@....edu> wrote:
> > On Tue, Feb 12, 2013 at 10:58:32PM +0100, Jan Kara wrote:
> > >   The third patch is a fix which shouldn't cause any issues. So you can
> > > take just that one and leave the other two aside until we are able to
> > > resolve the issue.
> > 
> > I thought the third patch depending on the first two?  Certainly it
> > doesn't apply cleanly without the first two patches...
> My patch fix old issue, but i've prepared it on top of Jan's patches
> only for simplicity. I'll send new version which not depend on his
> patches today.
> Over-all Jan's statment that split should not happen inside end_io
> and it is clear sing of a bug is absolutely right decision.
> This helps us to spot several hidden issues (number is still unknown)
> so may be it is reasonable to split first patch in two parts:
> 1) disable uninitialized extents merging itself.
> 2) Print warning if split is required inside end_io(so only warning will
> be printed, but w/o data corruption)
> 3) Get rid of extent split machinery from end_io (because it is not
> longer valid situation)
> 
> (1) and (2) should be accepted ASAP and will help us to spot and fix
> other hidden issues. And we fix all related issues it will be safe
> to apply (3)'rd one.
> I'll send patches soon.
  I agree with this plan, I just think the warnings are currently too easy
to trigger (just random AIO DIO writing seems to trigger them with
dioread_nolock) so as Ted said we'll probably have to hide them under
EXT4_DEBUG or something like that. I'll try to debug the current problem
while you prepare the patches :).

								Honza

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