linux-ext4 - Re: Question on block group allocation

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Date:	Wed, 29 Apr 2009 11:38:49 -0700
From:	Curt Wohlgemuth <curtw@...gle.com>
To:	Theodore Tso <tytso@....edu>
Cc:	G@....edu, Andreas Dilger <adilger@....com>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: Question on block group allocation

Hi Ted:

On Mon, Apr 27, 2009 at 3:40 PM, Theodore Tso <tytso@....edu> wrote:
> On Sun, Apr 26, 2009 at 11:29:39PM -0600, Curt Wohlgemuth wrote:
>> The random read throughput on the 10GB file went from ~16 MB/s to ~22
>> MB/s after Andreas' patch; the total fragmentation of the file was
>> much lower than before his patch.
>>
>> However, the number of extents went up by quite a bit (I don't have
>> the debugfs output in front of me at the moment, sorry).
>
> I'm curious what you meant by the combination of these two statements,
> "the total fragmentation of the file was much lower than before his
> patch", and "the number of extents went up by quite a bit".  Can you
> send me the debugfs output when you have a chance?

Sorry it's been so long for me to reply.

Okay, my phrasing was not as precise as it could have been.  What I
meant by "total fragmentation" was simply that the range of physical
blocks for the 10GB file was much lower with Andreas' patch:

Before patch:  8282112 - 103266303
After patch: 271360 - 5074943

The number of extents is much larger.  See the attached debugfs output.

Here's the output of "e2fsck -E fragcheck" on the block devices;
remember, though, that each one has only 3 files:

-rw-rw-r--    1 root     root     10737418240 Apr 23 15:33 10g
-rw-rw-r--    1 root     root     4294967296 Apr 23 15:30 4g
-rw-rw-r--    1 root     root     4294967296 Apr 23 15:30 4g-2
drwx------    2 root     root        16384 Apr 23 15:27 lost+found/

Before patch:
e2fsck 1.41.3 (12-Oct-2008)
/dev/hdm3: clean, 14/45760512 files, 7608255/183010471 blocks

After patch:
e2fsck 1.41.3 (12-Oct-2008)
/dev/hdo3: clean, 14/45760512 files, 7608258/183010471 blocks


Thanks,
Curt

Download attachment "debugfs.before-patch" of type "application/octet-stream" (888 bytes)

Download attachment "debugfs.after-patch" of type "application/octet-stream" (12951 bytes)