[libvirt-users] HugePages - can't start guest that requires them

[G. Richard Bellamy]

On Sun, Feb 22, 2015 at 11:01 PM, Michal Privoznik <mprivozn at redhat.com> wrote:
> Just drop the hard_limit. It's a blackbox we should had never
> introduced. In Linux, from kernel's POV, there's no difference between
> guest RAM and hypervisor memory to store its internal state. It's all
> one big chunk of memory. And even if you know the first part (how much
> memory you're letting guest to have), you don't know anything about the
> other part - how much memory does hypervisor need to store its internal
> state (which may even change over the time), therefore you can't tell
> the sum of both parts.
>
> Also, in the config of your VM, you're not using hugepages. Or you've
> just posted wrong XML?
>
> Then again, kernel's approach to hugepages is not as awesome as to
> regular system pages. Either on boot (1GB) or at runtime (2MB) one must
> cut a slice of memory off to be used by hugepages and nothing else. So
> even if you have ~17GB RAM free on both nodes, they are reserved for
> hugepages, hence the OOM.

Yeah, I dropped the hard limit, and have set <hugepages/>. I had the
hard limit set since I had also tried locking the pages in memory...
found out that was no bueno too.

I also ported numad to Arch Linux [1] and am using placement='auto',
which seems to be working reasonably well. I'll keep you posted.
Course, this required a custom build of libvirt [2] to get the NUMAD
defines set...

[1.0] https://aur.archlinux.org/packages/numad-git/
[1.1] https://aur.archlinux.org/packages/numad/
[2] https://github.com/rbellamy/pkgbuilds/tree/master/libvirt-git