Comment 2 for bug 1771810

Agreed that this enhancement will be either part of handling a down cell or moving to count quota usage from placement.

On the latter, we're currently blocked from moving to counting usage from placement because placement has no way to differentiate resource ownership among many potential services. So, calling the placement /usages API will return resource usage for all services that have added allocations to placement, not only a particular instance of nova.

Like Matt said, the best we could do at present is leverage the instance_mappings table to filter which cells we count for quota usage, like we do for instance list.

Looking at the nova/quota.py code, I see that we should also do the same for server group members. We have to count them by user and we don't have 'user_id' in the instance_mappings table, but we could at least filter on the project_id for choosing which cells to query.