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

[Michal Privoznik]

On 20.02.2015 21:32, G. Richard Bellamy wrote:
> <snip/>
>
> I've modified my config [1] based on my understanding, and am running
> into a new error. Basically I'm hitting the oom-killer [2] even though
> the hard_limit [3] of memtune is below the total number of hugepages
> set for that NUMA nodeset.
> 

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.


Michal