linux-ext4 - Re: [PATCH] ext4: Fix small file fragmentation

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Date:	Fri, 15 Aug 2008 23:37:45 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Theodore Tso <tytso@....edu>
Cc:	cmm@...ibm.com, sandeen@...hat.com, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: Fix small file fragmentation

On Fri, Aug 15, 2008 at 11:22:43PM +0530, Aneesh Kumar K.V wrote:
> On Thu, Aug 14, 2008 at 07:18:17PM -0400, Theodore Tso wrote:
> > On Thu, Aug 14, 2008 at 11:14:40PM +0530, Aneesh Kumar K.V wrote:
> > > mballoc small file block allocation use per cpu prealloc
> > > space. Use goal block when searching for the right prealloc
> > > space. Also make sure ext4_da_writepages tries to write
> > > all the pages for small files in single attempt
> > 
> > Hi Aneesh, how are you testing your patch?  I've created the following
> > shell script:
> > 
> > -------------------------------
> > #!/bin/sh
> > #
> > # small-files-frag-test --- test for small files fragmentation
> > 
> > DEVICE=/dev/thunk/testbench
> > 
> > mke2fs -t ext4dev $DEVICE
> > mount -t ext4dev $DEVICE /mnt
> > tar -C /usr -cf - bin lib | tar -C /mnt -xpf - 
> > sync; sleep 5
> > umount $DEVICE
> > e2fsck -nfv -E fragcheck $DEVICE
> > -------------------------------
> > 
> > ... and the results show roughly the same amount of fragmentation, and the
> > same pattern.  In fact, it's a ltitle worse (30% vs 25%).
> > 
> >    37912 inodes used (11.57%)
> >    11468 non-contiguous inodes (30.2%)
> >          # of inodes with ind/dind/tind blocks: 0/0/0
> >          Extent depth histogram: 32638/5
> >   711894 blocks used (54.31%)
> > 
> 
> 
> I have better results with the below patch on top of the patch i sent.
> 
>    21156 inodes used (0.47%)
>      158 non-contiguous inodes (0.7%)
>          # of inodes with ind/dind/tind blocks: 4/4/4
>   581216 blocks used (3.24%)
>        0 bad blocks
>        1 large file
> 

And the fragmented inodes are all directories for which we don't
use prealloc space

debugfs:  ncheck 12
Inode   Pathname
12      /bin
debugfs:  ncheck 1987
Inode   Pathname
1987    /lib
debugfs:  ncheck 7657
Inode   Pathname
7657    /lib/python2.5
debugfs:  ncheck 11602
Inode   Pathname
11602   /lib/X11/xserver
debugfs:  ncheck 14279
Inode   Pathname
14279   /lib/locale
debugfs:  ncheck 20615
Inode   Pathname
20615   /lib/ooo-2.0/program
debugfs:

-aneesh
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