On Wed, Sep 27, 2017 at 11:58 AM, Jakub Jursa
<[email protected]> wrote:
On 27.09.2017 11:12, Jakub Jursa wrote:
On 27.09.2017 10:40, Blair Bethwaite wrote:
On 27 September 2017 at 18:14, Stephen Finucane
<[email protected]> wrote:
What you're probably looking for is the 'reserved_host_memory_mb'
option. This
defaults to 512 (at least in the latest master) so if you up this
to 4192 or
similar you should resolve the issue.
I don't see how this would help given the problem description -
reserved_host_memory_mb would only help avoid causing OOM when
launching the last guest that would otherwise fit on a host based
on
Nova's simplified notion of memory capacity. It sounds like both
CPU
and NUMA pinning are in play here, otherwise the host would have no
problem allocating RAM on a different NUMA node and OOM would be
avoided.
I'm not quite sure if/how OpenStack handles NUMA pinning (why is VM
being killed by OOM rather than having memory allocated on different
NUMA node). Anyway, good point, thank you, I should have a look at
exact
parameters passed to QEMU when using CPU pinning.
Jakub, your numbers sound reasonable to me, i.e., use 60 out of
64GB
Hm, but the question is, how to prevent having some smaller instance
(e.g. 2GB RAM) scheduled on such NUMA node?
when only considering QEMU overhead - however I would expect that
might be a problem on NUMA node0 where there will be extra
reserved
memory regions for kernel and devices. In such a configuration
where
you are wanting to pin multiple guests into each of multiple NUMA
nodes I think you may end up needing different flavor/instance-type
configs (using less RAM) for node0 versus other NUMA nodes. Suggest
What do you mean using different flavor? From what I understand (
http://specs.openstack.org/openstack/nova-specs/specs/juno/implemented/virt-driver-numa-placement.html
https://docs.openstack.org/nova/pike/admin/cpu-topologies.html ) it
can
be specified that flavor 'wants' different amount memory from its
(virtual) NUMA nodes, but mapping vCPU <-> pCPU is more or less
arbitrary (meaning that there is no way how to specify for NUMA
node0 on
physical host that it has less memory available for VM allocation)
Can't be 'reserved_huge_pages' option used to reserve memory on
certain
NUMA nodes?
https://docs.openstack.org/ocata/config-reference/compute/config-options.html
I think the qemu memory overhead is allocated from the 4k memory pool
so the question is if it is possible to reserve 4k pages with the
reserved_huge_pages config option. I don't find any restriction in the
code base about 4k pages (even if it is not considered as a large page
by definition) so in theory you can do it. However this also means you
have to enable NumaTopologyFilter.
Cheers,
gibi
freshly booting one of your hypervisors and then with no guests
running take a look at e.g. /proc/buddyinfo/ and /proc/zoneinfo to
see
what memory is used/available and where.
Thanks, I'll look into it.
Regards,
Jakub
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