XFS ignores all atime related mount options, noatime is always in effect, documentation misses this information

[Roland Eggner]

On my linux box I tried to achieve regular atime behaviour, tried mount with
no atime related option at all, tried mount options atime, sync,
osyncisosync, .. XFS on plain partitions, on loop devices .. I tried another
kernel (sidux image with kernel 2.6.25-9) ..

My result:
It seems impossible to switch off "noatime" mount option.
atime updates happen only in core, never on disk unless coinciding with other
inode modifications, regardless of specified mount options.

$ uname -a
Linux roland 2.6.23.12roland2 #2 Tue Apr 15 17:10:52 CEST 2008 i686 GNU/Linux

$ zgrep XFS /proc/config.gz
CONFIG_XFS_FS=m
# CONFIG_XFS_QUOTA is not set
CONFIG_XFS_SECURITY=y
CONFIG_XFS_POSIX_ACL=y
CONFIG_XFS_RT=y
# CONFIG_VXFS_FS is not set

In mailing list archive I found
http://oss.sgi.com/archives/xfs/2007-10/msg00168.html
It seems, that 3 years ago an unconditional noatime enforcement has been
introduced.

(1) If this is true, please update documentation accordingly.
Users, who need a filesystem with regular atime behaviour, will no more waste
their time to try XFS, when in fact it is unusable for their particular
requirements.

(2) If I missed a possibility to achieve regular atime behaviour, please
document it in Documentation/filesystems/xfs.txt and in man 8 mount.

Thanks!

--
Roland Eggner

[Martin Steigerwald]

Am Donnerstag 18 Dezember 2008 schrieb Roland Eggner:
> On my linux box I tried to achieve regular atime behaviour, tried mount
> with no atime related option at all, tried mount options atime, sync,
> osyncisosync, .. XFS on plain partitions, on loop devices .. I tried
> another kernel (sidux image with kernel 2.6.25-9) ..
>
> My result:
> It seems impossible to switch off "noatime" mount option.
> atime updates happen only in core, never on disk unless coinciding with
> other inode modifications, regardless of specified mount options.
>
> $ uname -a
> Linux roland 2.6.23.12roland2 #2 Tue Apr 15 17:10:52 CEST 2008 i686
> GNU/Linux

I can't reproduce this on 2.6.27.7:

***@shambhala:~/Zeit> grep /home /proc/mounts
/dev/sda5 /home xfs
rw,relatime,attr2,nobarrier,logbufs=8,logbsize=256k,noquota 0 0
***@shambhala:~/Zeit> echo "hallo" >hallo.txt
***@shambhala:~/Zeit> ls -l --time=atime hallo.txt
-rw-r--r-- 1 martin martin 6 19. Dez 13:56 hallo.txt
***@shambhala:~/Zeit> cat hallo.txt ; ls -l --time=atime hallo.txt
hallo
-rw-r--r-- 1 martin martin 6 19. Dez 13:57 hallo.txt

How did you test it? A reproducable test case would be fine.

> $ zgrep XFS /proc/config.gz
> CONFIG_XFS_FS=m
> # CONFIG_XFS_QUOTA is not set
> CONFIG_XFS_SECURITY=y
> CONFIG_XFS_POSIX_ACL=y
> CONFIG_XFS_RT=y
> # CONFIG_VXFS_FS is not set

***@shambhala:~> zgrep XFS /proc/config.gz
CONFIG_XFS_FS=y
CONFIG_XFS_QUOTA=y
CONFIG_XFS_POSIX_ACL=y
CONFIG_XFS_RT=y
# CONFIG_XFS_DEBUG is not set
# CONFIG_VXFS_FS is not set

> In mailing list archive I found
> http://oss.sgi.com/archives/xfs/2007-10/msg00168.html
> It seems, that 3 years ago an unconditional noatime enforcement has
> been introduced.

Did you look within the same mount or did you unmount and remount first? I
remember there has been some issue with inode updates and unmounting, but
I do not remember the details.

> (2) If I missed a possibility to achieve regular atime behaviour,
> please document it in Documentation/filesystems/xfs.txt and in man 8
> mount.

Its either atime, relatime or noatime as mount option.

Ciao,
--
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
GPG: 03B0 0D6C 0040 0710 4AFA B82F 991B EAAC A599 84C7