linux-ext4 - Re: [PATCH 2/2] ext4: fix bug in ext4_mb_normalize

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Date:	Wed, 11 Jun 2014 10:47:19 +0200
From:	Maurizio Lombardi <mlombard@...hat.com>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	Lukáš Czerner <lczerner@...hat.com>,
	adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 2/2] ext4: fix bug in ext4_mb_normalize_request()

On Tue, Jun 03, 2014 at 04:36:39PM -0400, Theodore Ts'o wrote:
> On Tue, Jun 03, 2014 at 08:43:40PM +0200, Lukáš Czerner wrote:
> > 
> > I think that leaving the alignment of the start offset for the small
> > files/allocation is not good idea. We might end up with suboptimal
> > file layout for smaller files. While this is not a big deal for
> > bigger files, with smaller ones it might cause some troubles.
> 
> I thought we were only aligning the start offset for files > 2MB?
>

That's true.

With my patch the behaviour changes slightly because it doesn't depend
only from the file size but also from the number of blocks per group.

So, if you create a filesystem with blocksize==1Kb and 1024 blocks per group, we will start
aligning the start offset for files with size > 1Mb (1Kb * 1024)

The alignment is not performed on small files unless you have
a very low number of blocks per group.

Maurizio Lombardi

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