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On 11/02/2016 02:52 PM, Jay Pipes wrote:
> On 11/01/2016 10:14 AM, Alex Xu wrote:
>> Currently we only update the resource usage with Placement API in the
>> instance claim and the available resource update periodic task. But
>> there is no claim for migration with placement API yet. This works is
>> tracked by https://bugs.launchpad.net/nova/+bug/1621709. In newton, we
>> only fix one bit which make the resource update periodic task works
>> correctly, then it will auto-heal everything. For the migration claim
>> part, that isn't the goal for newton release.
>>
>> So the first question is do we want to fix it in this release? If the
>> answer is yes, there have a concern need to discuss.
>
> Yes, I believe we should fix the underlying problem in Ocata. The underlying
> problem is what Sylvain brought up: live migrations do not currently use any
> sort of claim operation. The periodic resource audit is relied upon to
> essentially clean up the state of claimed resources over time, and as Chris
> points out in review comments on https://review.openstack.org/#/c/244489/, this
> leads to the scheduler operating on stale data and can lead to an increase in
> retry operations.

It's worse than that.  For pinned instances it can result in vCPUs from multiple 
instances running on the same host pCPUs (which defeats the whole point of 
pinning), and can result in outright live migration failures if the destination 
has fewer pCPUs or NUMA nodes than the source.

> I see no reason why we can't change the behaviour of the `PUT
> /allocations/{consumer_uuid}` call to allow changing either the amounts of the
> allocated resources (a resize operation) or the set of resource provider UUIDs
> referenced in the allocations list (a move operation).

Agreed, your example looks reasonable at first glance.

Chris