[linuxkernelnewbies] polishlinux.org » Ext4 defragme ntation with e4defrag

Fri, 16 Jan 2009 16:42:07 -0800

http://polishlinux.org/apps/cli/ext4-defragmentation-with-e4defrag/

Ext4 defragmentation with e4defrag

[ Saturday, 31 May 2008, optimizationkit ]

Lately I have described ok_defrag — a simple tool for defragmenting Linux file systems. Today, I want to describe a specialized program designed to defrag the new Ext4 file system.

(For all who would like to say that Linux file systems don’t require defragmenting: Please redirect your great ideas to the Ext4 developers. They are the authors of this program — I do not have anything in common with it. As it will turn out, Ext4 is indeed quite different than other Linux file systems. Thanks in advance for your understanding)

To begin playing with e4defrag we must start compile of new kernel with patches needed to carry out the defragmentation. Below you will find a short description of that process, and if you would not like to use all those experimental patches for Ext4, then you should be interested in these seven only:

ext4-online-defrag-exchange-blocks-between-two-inodes.patch
ext4-online-defrag-relocate-file-data.patch
ext4-online-defrag-alloc-contiguous-blks.patch
ext4-online-defrag-ext4-defrag.patch
ext4-online-defrag-for-relevant-files.patch
ext4-online-defrag-check-for-freespace-fragmentation.patch
ext4-online-defrag-move-victim-files.patch

In first step we start from creation of directory, grabbing the kernel source, and downloading and unpacking needed patches.

mkdir linux-2.6-ext4
cd linux-2.6-ext4/
ketchup -G 2.6-git
wget http://www.kernel.org/pub/linux/kernel/people/tytso/\\
ext4-patches/2.6.26-rc2-git5-ext4-1/broken-out.tar.bz2
tar xjvf broken-out.tar.bz2
mv broken-out patches

Then we apply the patches on the sources.

quilt push -a

Then we start a process of configuring/building our new system kernel.

cp /our/beloved/.config .
cp /our/beloved/script/for/building/system/kernel/build.sh .

(on my PC it look like this:)

#!/bin/sh 

VER=`ketchup -m` 

make
sudo make modules_install
sudo cp arch/x86/boot/bzImage /boot/vmlinuz-$VER
sudo cp System.map /boot/System.map-$VER
sudo /sbin/new-kernel-pkg --mkinitrd --depmod --install $VER
)
make oldconfig
./build.sh

Meanwhile, when our new kernel compiles, we may open file: linux-2.6-ext4/patches/ext4-online-defrag-command.patch in our text editor of choice and we delete all lines from 1 to 18, and then from 1932 to 1935. Then, we copy our source code to other location.

cp linux-2.6-ext4/patches/ext4-online-defrag-command.patch e4defrag.c

And compile…

gcc -Wall e4defrag.c -o e4defrag

It is worth to grab some tools to handle the Ext4 file systems (the very latest version from the code repository).

git-clone git://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git
cd e2fsprogs
./configure
make
make install

After running our system with brand new kernel for the first time, we can finally start to test e4defrag. First we create and mount a test file system.

dd if=/dev/zero of=fs.img bs=256M count=1
/sbin/mkfs.ext3 fs.img

Now we must allow the use of experimental code on that partition.

/sbin/debugfs -w fs.img
debugfs 1.41-WIP (27-Apr-2008)
debugfs:  set_super_value s_flags 4
debugfs:  quit

Now our new file system is ready to be mounted

mount -t ext4dev -o loop,extents fs.img /mnt/loop0/

How to cause fragmentation at Ext4? - I have not yet tested any good way for fast fragmenting Ext4. This file system contrary to other Linux file systems is exceptionally resistant to fragmentation.

 /sbin/fsck.ext3 -nfv fs.img
e2fsck 1.41-WIP (27-Apr-2008)
First  course: checking i-nodes, blocks and sizes
Second course: checking directory structure
Third  course: checking communications directories
Fourth course: checking counters appeals
Fifth  course: checking the summary information about groups

     368 inodes used (0.56%)
       1 non-contiguous inode (0.3%)
         number i-nodes with blocks ind/dind/tind: 136/129/129
  202885 blocks used (77.39%)
       0 bad blocks
       0 large files 

     351 regular files
       8 directories
       0 character device files
       0 block device files
       0 fifos
       0 links
       0 symbolic links (0 fast symbolic links)
       0 sockets
--------
     359 files

It seems that Ext4 is a tough row to hoe, but its developers still deliver a defragmentation tool for it. Take a peep!

With use e4defrag we can defrag single files, for example:

e4defrag /patch/to/file

or all directories:

e4defrag -r /patch/to/directory/

also, there is a way to defrag a partition:

e4defrag /dev/sda1
e4defrag file_system_image.img

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