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Date: Sun, 20 Feb 2011 10:06:56 +0100
From: Rogier Wolff <R.E.Wolff@...Wizard.nl>
To: linux-ext4@...r.kernel.org
Subject: fsck performance.
Hi,
I was running debian-stable, on my backup-server (the server that
does backups, not the "just-in-case" server).
Debian apparently recently pointed that to the new release squeeze, so
I got upgraded. I went from kernel 2.6.26 to 2.6.32. After about a day
my system rebooted without my consent. So now it's running 2.6.32.
Since then I'm getting kernel-oops-lookalikes that start with:
[71664.306573] swapper: page allocation failure. order:5, mode:0x4020
Lots of them actually.
(on the other hand, none of these happened before my filesystem got
thrashed...)
Anyway, upon boot into the new kernel ext3 printed abunch of these:
[ 5.212119] ext3_orphan_cleanup: deleting unreferenced inode 1335743
A few hours later, my storage partition was marked read-only and the
backups started failing.
kern.log.1.gz:Feb 18 05:39:53 driepoot kernel: [10328.424778]
EXT3-fs error (device md3): ext3_lookup: deleted inode referenced: 277447722
So to correct the situation I started an fsck.
After about 24 hours, I decided that the fsck was taking too long and
decided to upgrade e2fsck. It has now been running for an hour and a
half. Now I don't mind fsck taking an hour or two. But I expect fsck
to be disk bound.
However iostat shows me it's doing next to nothing for seconds
at a time:
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
md3 0.00 0.00 0.00 0 0
md3 0.00 0.00 0.00 0 0
md3 0.00 0.00 0.00 0 0
md3 733.33 2933.33 0.00 2904 0
md3 0.00 0.00 0.00 0 0
md3 63.37 253.47 0.00 256 0
md3 0.00 0.00 0.00 0 0
md3 0.00 0.00 0.00 0 0
md3 5.88 23.53 0.00 24 0
and it turns out that fsck is completely CPU bound:
top - 09:26:29 up 2 days, 6:38, 10 users, load average: 1.06, 1.07, 1.27
Tasks: 136 total, 2 running, 134 sleeping, 0 stopped, 0 zombie
Cpu(s): 79.1%us, 4.9%sy, 0.0%ni, 0.0%id, 0.4%wa, 1.5%hi, 14.1%si, 0.0%st
Mem: 969400k total, 956624k used, 12776k free, 226828k buffers
Swap: 1975976k total, 252220k used, 1723756k free, 67768k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
10274 root 20 0 839m 631m 52m R 97.7 66.7 50:07.09 e2fsck
and when I trace fsck I get:
fcntl64(6, F_SETLKW, {type=F_WRLCK, whence=SEEK_SET, start=164, len=1}) = 0
fcntl64(6, F_SETLKW, {type=F_UNLCK, whence=SEEK_SET, start=164, len=1}) = 0
fcntl64(6, F_SETLKW, {type=F_UNLCK, whence=SEEK_SET, start=264, len=1}) = 0
fcntl64(5, F_SETLKW, {type=F_WRLCK, whence=SEEK_SET, start=572, len=1}) = 0
fcntl64(5, F_SETLKW, {type=F_WRLCK, whence=SEEK_SET, start=164, len=1}) = 0
fcntl64(5, F_SETLKW, {type=F_UNLCK, whence=SEEK_SET, start=164, len=1}) = 0
fcntl64(5, F_SETLKW, {type=F_UNLCK, whence=SEEK_SET, start=572, len=1}) = 0
fcntl64(6, F_SETLKW, {type=F_WRLCK, whence=SEEK_SET, start=572, len=1}) = 0
fcntl64(6, F_SETLKW, {type=F_WRLCK, whence=SEEK_SET, start=164, len=1}) = 0
So, my question is: Are these fcntl calls neccesary?
As far as I know locking is neccesary if another process might be
handling the same data. Here is is doing this with the cache
files:
lrwx------ 1 root root 64 Feb 20 09:28 5 ->
/var/cache/e2fsck/123a1cfe-2455-4646-aa32-87492ed1ac97-icount-ayxVou
lrwx------ 1 root root 64 Feb 20 09:28 6 ->
/var/cache/e2fsck/123a1cfe-2455-4646-aa32-87492ed1ac97-dirinfo-rBBTtb
were, using these swap files makes sense as some machines don't have
the memory and/or addressingspace to handle a big fsck, but in my
case I have 1G RAM, and these two files are 56M total:
-rw------- 1 root root 21M Feb 20 09:30 ...97-dirinfo-rBBTtb
-rw------- 1 root root 35M Feb 20 09:30 ...97-icount-ayxVou
# strace -p 10274 | & head -100000 | sort | uniq -c | sort -n
shows me that out of 100k system calls
10876 fcntl64(6, F_SETLKW, {type=F_UNLCK, whence=SEEK_SET, start=164, len=1}) = 0
10877 fcntl64(6, F_SETLKW, {type=F_WRLCK, whence=SEEK_SET, start=164, len=1}) = 0
13339 fcntl64(5, F_SETLKW, {type=F_UNLCK, whence=SEEK_SET, start=164, len=1}) = 0
13339 fcntl64(5, F_SETLKW, {type=F_WRLCK, whence=SEEK_SET, start=164, len=1}) = 0
and 60-139 locks for different locations.
Oh... and fsck is now at the stage:
Pass 1: Checking inodes, blocks, and sizes
The filesystem is 3T:
md3 : active raid5 sda3[0] sdd3[3] sdc3[2] sdb3[1]
2868686592 blocks level 5, 256k chunk, algorithm 2 [4/4] [UUUU]
I'm studying e2fsck source code abit, but I don't yet see where the
fcntl calls are coming from.
Roger.
--
** R.E.Wolff@...Wizard.nl ** http://www.BitWizard.nl/ ** +31-15-2600998 **
** Delftechpark 26 2628 XH Delft, The Netherlands. KVK: 27239233 **
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