linux-ext4 - Re: [PATCH 01/11 RESEND] libe2p: Add new function get_fragment

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Message-Id: <A947D80A-0C4E-4079-B233-E890677BFDEF@dilger.ca>
Date:	Sat, 18 Jun 2011 11:15:31 -0600
From:	Andreas Dilger <adilger@...ger.ca>
To:	Greg Freemyer <greg.freemyer@...il.com>
Cc:	Eric Sandeen <sandeen@...hat.com>, Ted Ts'o <tytso@....edu>,
	Kazuya Mio <k-mio@...jp.nec.com>,
	ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 01/11 RESEND] libe2p: Add new function get_fragment_score()

On 2011-06-18, at 11:00 AM, Greg Freemyer <greg.freemyer@...il.com> wrote:
> On Sat, Jun 18, 2011 at 3:19 AM, Andreas Dilger <aedilger@...il.com> wrote:
>> I was thinking about this, and am wondering if it makes sense to have an absolute score for fragmentation instead of a relative one?
>> 
>> By absolute I mean something like fragments per MB or similar. A bad score might be anything > 1. For files smaller than 1 MB in size it would scale the ratio to the equivalent if the file was 1MB in size (e.g. a 16kB file with 4 fragments would have a score of 256, which is clearly bad).  Large files can have a score much less than 1, which is good.
>> 
>> Cheers, Andreas
> 
> Shouldn't be based on fragments per max extent size for ext4?
> 
> And I think the max extent size for a 4KB page is 128 MB, right?

I was thinking about that, but in most cases it is unrealistic that all files have 128MB extents except on empty test filesystems, and I don't think that files with "only" 32MB extents should be considered that badly off.

I don't particularly care what the exact scale is, but I like the idea of an absolute measure instead of a relative measure (i.e. 33% fragmented).

Cheers, Andreas--
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