When creating the allocation for the instance, we lookup the flavor to know the disk sizes for root, ephemeral and gb and we basically sum them.
https://github.com/openstack/nova/blob/7d04c78c1e2c26125eff5b1a8543b1ac5d027107/nova/scheduler/client/report.py#L129-L131
Unfortunately, since both root and ephemeral size are expressed in GB while swap is expressed in MB, the sum is not good.
See how the DiskFilter works for accounting resources : https://github.com/openstack/nova/blob/3cafa7f5bd0775b8ba49080226c03f8a91468d7d/nova/scheduler/filters/disk_filter.py#L36-L38
We should change the logic to ceil to the next GB if modulo(root + ephemeral * 1024 + swap / 1024) is not rounded to 0 since we want to count allocations as the Inventory only counts by GB.
That's suboptimal and a long-term solution would be to report inventories in bytes (as the smallest attribute) but that's a big change so probably requiring a BP.
Does https:/