[HEADS-UP] Moving /var/run and /var/lock to tmpfs in Rawhide

Lennart Poettering mzerqung at 0pointer.de
Tue Nov 23 22:54:47 UTC 2010

On Tue, 23.11.10 13:41, Nicholas Miell (nmiell at gmail.com) wrote:

> On 11/23/2010 12:48 PM, Lennart Poettering wrote:
> > Heya!
> > 
> > I hereby want to let everybody know that in the next days I will turn on
> > /var/run and /var/lock on tmpfs on Rawhide/F15. This is in accordance
> > with the following accepted F15 feature:
> > 
> > https://fedoraproject.org/wiki/Features/var-run-tmpfs
> > 
> Is this actually an improvement?

See the spec page.

I think the fact that we get less disks accesses (just think noatime and
stuff for the files dropped there) is more interesting than using the
absolute minimal amount of memory.

> I know that dentries and inodes for regular filesystems can be discarded
> from RAM if they're not in use, is that the case for a tmpfs?
> How often are the files in /var/run and /var/lock accessed? Is the
> kernel likely to discard them?

Note that under memory pressure tmpfs can be swapped out.

> Files in /var/run tend to be 4 or 5 bytes in length, does that mean they
> each use an entire page of RAM or swap? There are vastly fewer swap
> pages than there are filesystem blocks, isn't this less efficient?

Yes, normal files will take up 4k if they contain data. But that's
something that could be fixed and which would not only be useful for
this usecase but the much heavier existing users of tmpfs such as udev.


Lennart Poettering - Red Hat, Inc.

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