[openstack-dev] [nova] NUMA, huge pages, and scheduling

Daniel P. Berrange berrange at redhat.com
Fri Jun 10 08:40:22 UTC 2016

On Thu, Jun 09, 2016 at 12:35:06PM -0600, Chris Friesen wrote:
> On 06/09/2016 05:15 AM, Paul Michali wrote:
> > 1) On the host, I was seeing 32768 huge pages, of 2MB size.
> Please check the number of huge pages _per host numa node_.
> > 2) I changed mem_page_size from 1024 to 2048 in the flavor, and then when VMs
> > were created, they were being evenly assigned to the two NUMA nodes. Each using
> > 1024 huge pages. At this point I could create more than half, but when there
> > were 1945 pages left, it failed to create a VM. Did it fail because the
> > mem_page_size was 2048 and the available pages were 1945, even though we were
> > only requesting 1024 pages?
> I do not think that "1024" is a valid page size (at least for x86).

Correct, 4k, 2M and 1GB are valid page sizes.

> Valid mem_page_size values are determined by the host CPU.  You do not need
> a larger page size for flavors with larger memory sizes.

Though note that page sizes should be a multiple of favour mem size
unless you want to waste memory. eg if you have a flavour with 750MB
RAM, then you probably don't want to use 1GB pages as it waste 250MB

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