Open Stack

Please remember to add a topic [nova] marker to your subject line. 
Answer below.

On 09/05/2017 04:45 AM, Weichih Lu wrote:
> Dear all,
> 
> I have a compute node with 64GB ram. And I set 50 hugepages wiht 1GB 
> hugepage size. I used command "free", it shows free memory is about 
> 12GB. And free hugepages is 50.

Correct. By assigning hugepages, you use the memory allocated to the 
hugepages.

> Then I launch an instance with 16GB memory, set flavor tag 
> : hw:mem_page_size=large. It show Error: No valid host was found. There 
> are not enough hosts available.

Right, because you have only 12G of RAM available after 
creating/allocating 50G out of your 64G.

Huge pages are entirely separate from the normal memory that a flavor 
consumes. The 16GB memory in your flavor is RAM consumed on the host. 
The huge pages are individual things that are consumed by the NUMA 
topology that your instance will take. RAM != huge pages. Totally 
different things.

  And I check nova-scheduler log. My
> compute is removed by RamFilter. I can launch an instance with 8GB 
> memory successfully, or I can launch an instance with 16GB memory 
> sucessfully by remove RamFilter.

That's because RamFilter doesn't deal with huge pages. Because huge 
pages are a different resource than memory. The page itself is the resource.

The NUMATopologyFilter is the scheduler filter that evaluates the huge 
page resources on a compute host and determines if the there are enough 
*pages* available for the instance. Note that I say *pages* because the 
unit of resource consumption for huge pages is not MB of RAM. It's a 
single memory page.

Please read this excellent article by Steve Gordon for information on 
what NUMA and huge pages are and how to use them in Nova:

http://redhatstackblog.redhat.com/2015/09/15/driving-in-the-fast-lane-huge-page-support-in-openstack-compute/

Best,
-jay

> Does RamFilter only check free memory but not free hugepages?
> How can I solve this problem?
> 
> I use openstack mitaka version.
> 
> thanks
> 
> WeiChih, Lu.
> 
> Best Regards.
> 
> 
> _______________________________________________
> Mailing list: http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack
> Post to     : openstack at lists.openstack.org
> Unsubscribe : http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack
>