Disabling atime

[Eric Sandeen]

Bill Crawford wrote:
> On 12/08/07, Ralf Corsepius <rc040203 at freenet.de> wrote:
> 
>> SELinux is completely optional and doesn't cause functional regression.
> 
> Stops warning or error messages from "modprobe" being logged to my X
> session log (~/X.log) if I'm in enforcing mode, because of the
> security context?
> 
>> Well, actually I think Fedora is derailing due to its leadership
>> committing one mistake after the other.
> 
> That's another issue :)
> 
> Why not default to "noatime" for all bar /tmp, and create that as a
> separate partition / logical volume by default? 


Because nobody has shown conclusively, at least no on this thread, that
noatime actually helps enough to matter, IMHO.

As far as I'm concerned, nobody has done the necessary legwork to
justify this change.

I have at least one case where noatime actually slows things down.  With
66 million inodes on an ext3 filesystem, "find" across the filesystem
with a fresh mount / cold cache was a few seconds slower with noatime.
Odd result, but it shows at least that this change shouldn't be made
based on a hunch, but only after looking at some real results.

-Eric


[root at bear-05 ~]# for I in `seq 1 10`
do
mount /dev/sdb12 /mnt/test
time find /mnt/test > /dev/null
umount /dev/sdb12
done

real    0m58.355s
user    0m0.384s
sys     0m1.212s

real    0m53.485s
user    0m0.400s
sys     0m1.236s

real    0m53.900s
user    0m0.348s
sys     0m1.288s

real    0m53.919s
user    0m0.328s
sys     0m1.080s

real    0m54.835s
user    0m0.288s
sys     0m1.316s

real    0m55.544s
user    0m0.348s
sys     0m1.332s

real    0m53.221s
user    0m0.376s
sys     0m1.332s

real    0m54.252s
user    0m0.308s
sys     0m1.300s

real    0m54.379s
user    0m0.344s
sys     0m1.192s

real    0m54.430s
user    0m0.364s
sys     0m1.188s
[root at bear-05 ~]# for I in `seq 1 10`; do mount -o noatime /dev/sdb12
/mnt/test; time find /mnt/test > /dev/null; umount /dev/sdb12; done

real    0m58.461s
user    0m0.380s
sys     0m1.052s

real    0m57.830s
user    0m0.336s
sys     0m1.180s

real    0m57.997s
user    0m0.356s
sys     0m1.236s

real    0m58.123s
user    0m0.348s
sys     0m1.228s

real    0m58.565s
user    0m0.352s
sys     0m1.132s

real    0m59.683s
user    0m0.332s
sys     0m1.292s

real    0m58.457s
user    0m0.408s
sys     0m1.096s

real    0m58.406s
user    0m0.344s
sys     0m1.240s

real    0m58.678s
user    0m0.332s
sys     0m1.192s

real    0m58.934s
user    0m0.376s
sys     0m1.308s