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Date: Fri, 6 Jun 2014 09:09:38 +0200 (CEST)
From: Lukáš Czerner <lczerner@...hat.com>
To: "Theodore Ts'o" <tytso@....edu>
cc: 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, 3 Jun 2014, Theodore Ts'o wrote:
> Date: Tue, 3 Jun 2014 16:36:39 -0400
> From: Theodore Ts'o <tytso@....edu>
> To: Lukáš Czerner <lczerner@...hat.com>
> Cc: Maurizio Lombardi <mlombard@...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 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?
>
> > Also I started looking into normalize_request and hopefully I'll
> > have a patch soon. Ted, do you have any suggestion for a test to
> > make sure that I do not make things worse ? You mentioned something
> > simple on LSF, but I do not remember what it was.
>
> The two mechanisms which we have currently are:
>
> 1) e2freefrag to measure free space fragmentation
Yes, that's what I am using along with e4defrag and debugfs -R
"dump_extents" to figure out what changed.
>
> 2) e2fsck -fE fragcheck /dev/sdXX
I was not aware of that, thanks. However I was more interested in
workload to test on. Right now I have a simple script which is
doing:
# Test fallocate time
echo "[+] Fallocate test"
time fallocate -l70G ${MNT}/file
do_freefrag
do_defrag ${MNT}/file
do_debugfs /file
rm -f ${MNT}/file
sync
# Copy linux source
echo "[+] Copy linux source"
cp -r $linux_source ${MNT}/linux1 &
cp -r $linux_source ${MNT}/linux2 &
time wait
do_freefrag
# Tar linux source
echo "[+] Tar linux source"
tar -cf ${MNT}/linux1_1.tar ${MNT}/linux1 &
tar -cf ${MNT}/linux1_2.tar ${MNT}/linux1 &
time wait
do_freefrag
do_defrag ${MNT}/linux1_1.tar
do_debugfs /linux1_1.tar
do_defrag ${MNT}/linux1_2.tar
do_debugfs /linux1_2.tar
# Untar linux source
echo "[+] Untar linux source"
mkdir ${MNT}/tt1
mkdir ${MNT}/tt2
tar -xf ${MNT}/linux1_1.tar -C ${MNT}/tt1 &
tar -xf ${MNT}/linux1_2.tar -C ${MNT}/tt2 &
time wait
do_freefrag
# Singe dd
echo "[+] Single dd"
time dd if=/dev/zero of=${MNT}/file bs=512 count=4194304
do_freefrag
do_defrag ${MNT}/file
do_debugfs /file
# Multiple dd test
echo "[+] Multiple dd"
# 2G
dd if=/dev/zero of=${MNT}/file0 bs=4096 count=524288 &
# 2G
dd if=/dev/urandom of=${MNT}/file1 bs=512 count=4194304 &
# 2G
dd if=/dev/zero of=${MNT}/file2 bs=1M count=2048 &
# 4M
dd if=/dev/zero of=${MNT}/file3 bs=4096 count=1024 &
# 16M
dd if=/dev/zero of=${MNT}/file4 bs=4096 count=4096 &
time wait
do_freefrag
do_defrag ${MNT}/file0
do_debugfs /file0
do_defrag ${MNT}/file1
do_debugfs /file1
do_defrag ${MNT}/file2
do_debugfs /file2
do_defrag ${MNT}/file3
do_debugfs /file3
do_defrag ${MNT}/file4
do_debugfs /file4
# Run fsstress
echo "[+] Run fsstress"
time $fsstress -s 123456 -p24 -n 999 -d $MNT
do_freefrag
do_defrag ${MNT}
And then do the same thing on the loop device and investigate the
underlying image file.
Thanks!
-Lukas
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