On 12/13/2012 01:00 AM, Garrett Holmstrom wrote: > On 2012-12-12 16:42, Matthew Miller wrote: >> The /tmp filesystem is on tmpfs by default in F18: >> http://fedoraproject.org/wiki/Features/tmp-on-tmpfs (and affirmed by >> FESCO >> here: https://fedorahosted.org/fesco/ticket/940#comment:45). >> >> I'm agnostic about this as a default for Fedora overall, but I can see >> it as >> problematic on cloud/virt guests where RAM is usually more >> constrained. (In >> fact, there's a bugzilla report to that effect here >> https://bugzilla.redhat.com/show_bug.cgi?id=858265). >> >> The feature page and release notes explicitly call out tmpfs as >> "Administrators can override this" so I don't think we would be going too >> far off the path if we disable it by default in the cloud images. >> >> What do you think? > > I can think of two trains of thought here: swap requirements and the > size of /tmp itself. > > The cost of putting /tmp on tmpfs in the worst-case scenario (the system > needs all of its RAM *and* /tmp is full) is half the amount of RAM's > worth of swap space. At least in my experience, once I'm forced to > create *any* swap space it doesn't really matter how large it is -- it's > trivial to bump the amount of swap a little higher, and the instance is > already likely to end up thrashing at some point anyway. So especially > on an I/O-constrained cloud, for me it really boils down to, "Am I going > to have to provision swap space or not?" > > For example, there's already one case of this happening even without > /tmp on tmpfs: a yum update on a t1.micro instance in EC2 may not > finish if the update happens to involve the system recompiling its > SELinux policy -- there simply isn't enough RAM to do everything. In > this case I don't really mind having /tmp on tmpfs since the system is > going to be unusable during that process anyway and I only have to add > around 300M of extra swap to compensate for the change. The pivotal > question for a given cloud and workload, then, is, "To how many > instances will tmp-on-tmpfs force me to add swap space?" > > The other case is, of course, the obvious one: how big does /tmp > actually have to be to run a reasonable Fedora server? Do we know what > is likely to break when /tmp is significantly smaller than usual? Most > of the distro's testing occurs on desktop/laptop machines with at least > 1 or 2 GB of memory, after all. > > There are enough cloud- and workload-specific variables here that I'm > not particularly enthusiastic about putting /tmp on tmpfs, so I'd > support masking that by default. Since doing so would be deviating from > Fedora's new default we should make sure to document that fact and tell > people how to turn it back on if we go that route, though. > > Those are my thoughts, at least. What do the rest of you think? > > -- > Garrett Holmstrom +1 /tmp NOT on tmpfs for default cloud image +1 document it very well Troy _______________________________________________ cloud mailing list cloud@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/cloud
