linux-ext4 - Re: [REGRESSION] allocated N with only M reserved metadata blocks

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Date:	Tue, 12 Mar 2013 10:48:27 +0100 (CET)
From:	Lukáš Czerner <lczerner@...hat.com>
To:	Lukáš Czerner <lczerner@...hat.com>
cc:	"Theodore Ts'o" <tytso@....edu>, Eric Whitney <enwlinux@...il.com>,
	linux-ext4@...r.kernel.org
Subject: Re: [REGRESSION] allocated N with only M reserved metadata blocks

On Tue, 12 Mar 2013, Lukáš Czerner wrote:

> Date: Tue, 12 Mar 2013 08:58:53 +0100 (CET)
> From: Lukáš Czerner <lczerner@...hat.com>
> To: Theodore Ts'o <tytso@....edu>
> Cc: Eric Whitney <enwlinux@...il.com>, linux-ext4@...r.kernel.org
> Subject: Re: [REGRESSION] allocated N with only M reserved metadata blocks
> 
> On Mon, 11 Mar 2013, Theodore Ts'o wrote:
> 
> > Date: Mon, 11 Mar 2013 17:22:39 -0400
> > From: Theodore Ts'o <tytso@....edu>
> > To: Eric Whitney <enwlinux@...il.com>
> > Cc: linux-ext4@...r.kernel.org
> > Subject: Re: [REGRESSION] allocated N with only M reserved metadata blocks
> > 
> > On Mon, Mar 11, 2013 at 05:02:01PM -0400, Eric Whitney wrote:
> > > 
> > > FWIW, this might not be a regression.  I believe I've got this warning in my
> > > testing logs from both 3.8 and 3.8-rc7 (commit 01a523eb51 in 3.9-rc1 affects
> > > message format and line numbering) on both x86 and ARM.  I didn't run xfstest
> > > 127 prior to 3.8-rc7, so I don't know how far back the warning may have
> > > occurred for that particular test.
> > > 
> > > The 3.8-rc7 results are a little different with respect to number of warnings
> > > and test cases, so I'm thinking this one isn't completely deterministic,
> > > testing-wise.  Multiple test runs may be required to see it.
> > 
> > Thanks for the extra data; this saved be a whole bunch of time, since
> > I probably would have started doing a series git bisects tonight.   :-)
> > 
> >   	   	      	      	      - Ted
> 
> I found that the problem is present even in 3.7.0, however it is not
> present in 3.6.0. I guess we need to bisect now :)
> 
> -Lukas

Apparently the problem is caused by the commit:

67a5da564f97f31c4054d358e00b34d7ee570da5 ext4: make the zero-out
chunk size tunable

Reverting that commit on 3.7 makes the warning disappear. I'll try
to see what's going on there, however from the nature of the change
it seems to me that the problem might have always been there but the
change just makes it easier/possible to hit. We'll see...

-Lukas