linux-ext4 - Re: [PATCH] ext4: optimize extent selection for block removal in case of hole punch

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Date:	Wed, 19 Jun 2013 21:14:53 +0530
From:	Ashish Sangwan <ashishsangwan2@...il.com>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	adilger@...ger.ca, ext4 development <linux-ext4@...r.kernel.org>,
	Ashish Sangwan <a.sangwan@...sung.com>,
	Namjae Jeon <namjae.jeon@...sung.com>
Subject: Re: [PATCH] ext4: optimize extent selection for block removal in case
 of hole punch

On Wed, Jun 19, 2013 at 7:36 PM, Theodore Ts'o <tytso@....edu> wrote:
> On Wed, Jun 19, 2013 at 07:15:35PM +0530, Ashish Sangwan wrote:
>> On Tue, Jun 18, 2013 at 9:10 PM, Theodore Ts'o <tytso@....edu> wrote:
>> > On Fri, May 24, 2013 at 08:09:17PM +0530, ashishsangwan2@...il.com wrote:
>> >> From: Ashish Sangwan <a.sangwan@...sung.com>
>> >>
>> >> Both hole punch and truncate use ext4_ext_rm_leaf for removing
>> >> blocks. Currently we choose the last extent as the starting
>> >> point for removing blocks: ex = EXT_LAST_EXTENT(eh);
>> >> This is OK for truncate but for hole punch we can optimize the
>> >> extent selection as the path is already initialized.
>> >> We could use this information to select proper starting extent.
>> >> The code change in this patch will not affect truncate as for
>> >> truncate path[depth].p_ext will always be NULL.
>> >>
>> >> Signed-off-by: Ashish Sangwan <a.sangwan@...sung.com>
>> >> Signed-off-by: Namjae Jeon <namjae.jeon@...sung.com>
>> >
>> > Applied, thanks.
>>
>> Sorry I cannot see the patch changes in ext4 dev branch.
>
> Sorry, I dropped this patch from the dev branch last night, but I
> didn't want to send e-mail about it until I had completed enough
> testing to be sure.  It appears that this patch is causing a
> regression; xfstests generic/269 and generic/279 to fail in the
> nojournal configuration.
>
Dropping this patch makes sense until root cause is not obvious.

> The tests are ones which have multiple fsstress threads racing with
> dd/ENOSPC hitters, with (#270) and without (#269) quota enabled.  It's
> not at all obvious to me why your particular change would make a
> difference here, and it may simply be that your optimization is
> exposing a timing change and is not the root cause of the failure, but
> I'm going to move this to the unstable portion of the patch series
> until we do further investigation.
>
> If you could take a look at this, I would appreciate it, but as I
> said, this may very well turn out not be the fault of your patch.
>
Sure, I will try looking into it.

Regards,
Ashish
> Regards,
>
>                                                 - Ted
>
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