[nova] Mempage fun

Chris Friesen chris.friesen at windriver.com
Thu Jan 10 16:08:05 UTC 2019

On 1/8/2019 12:38 PM, Stephen Finucane wrote:

> I have (1) fixed here:
>    https://review.openstack.org/#/c/629281/
> That said, I'm not sure if it's the best thing to do. From what I'm
> hearing, it seems the advice we should be giving is to not mix
> instances with/without NUMA topologies, with/without hugepages and
> with/without CPU pinning. We've only documented the latter, as
> discussed on this related bug by cfriesen:
>    https://bugs.launchpad.net/nova/+bug/1792985
> Given that we should be advising folks not to mix these (something I
> wasn't aware of until now), what does the original patch actually give
> us?

I think we should look at it from the other direction...what is the 
ultimate *desired* behaviour?

Personally, I'm coming at it from a "small-cloud" perspective where we 
may only have one or two compute nodes.  As such, the host-aggregate 
solution doesn't really work.

I would like to be able to run cpu-pinned and cpu-shared instances on 
the same node.  I would like to run small-page (with overcommit) and 
huge-page (without overcommit) instances on the same node.  I would like 
to run cpu-shared/small-page instances (which float over the whole host) 
on the same host as a cpu-pinned/small-page instance (which is pinned to 
specific NUMA nodes).

We have a warning in the docs currently that is specifically for 
separating CPU-pinned and CPU-shared instances, but we also have a spec 
that plans to specifically support that case.  The way the code is 
currently written we also need to separate NUMA-affined small-page 
instances from non-NUMA-affined small-page instances, but I think that's 
a bug, not a sensible design.


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