Hi all,
While I was working on fixing the resize for pci passthrough [1] I have notice the following issue in resize.
If you are using small image and you resize-confirm it very fast the old resources are not getting freed.
After debug this issue I found out the root cause of it.
A Good run of resize is as detailed below:
When doing resize the _update_usage_from_migration in the resource trucker called twice.
1. The first call we return the instance type of the new flavor and will enter this case
https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L718
2. Then it will put in the tracked_migrations the migration and the new instance_type
https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L763
3. The second call we return the old instance_type and will enter this case
https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L725
4. Then in the tracked_migrations it will overwrite the old value with migration and the old instance type
5. https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L763
6. When doing resize-confirm the drop_move_claim called with the old instance type
https://github.com/openstack/nova/blob/9a05d38f48ef0f630c5e49e332075b273cee38b9/nova/compute/manager.py#L3369
7. The drop_move_claim will compare the instance_type[id] from the tracked_migrations to the instance_type.id (which is the old one)
8. And because they are equals it will remove the old resource usage
https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L315-L328
But with small image like CirrOS and doing the revert-confirm fast the second call of _update_usage_from_migration will not get executing.
The result is that when we enter the drop_move_claim it compares it with the new instance_type and this expression is false https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L314
This mean that this code block is not executed https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L315-L326 and therefore old resources are not getting freed.
Any thought on the matter?
[1] - https://review.openstack.org/#/c/307124/
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