Obviously, all consumers are currently Nova instances in placement since (AFAIK) no other services have begun using placement to store allocations.
This is not the case, actually. In Nova, we can have consumers that are instances, as well as consumers that are migrations (related to instances, but distinct). In order to be able to distinguish between the two, a partitioning key (I'd prefer we call this consumer type too) is needed. The quota work needs this specifically, so that we can know the usage by instances separately from usage that is reserved or pinned by an ongoing migration.
How urgent is this? Is there anyone available to do the work this cycle? How damaging is it to punt to U? What details are missing in the above description?
I guess we defer this question to Melanie, but I think the ability to count most of the quota elements we want using placement instead of the current method hinges on the ability to distinguish these things. --Dan