[placement][ptg] Allocation Partitioning

Surya Seetharaman surya.seetharaman9 at gmail.com
Wed Apr 17 08:45:40 UTC 2019

On Tue, Apr 16, 2019 at 11:05 PM melanie witt <melwittt at gmail.com> wrote:

> On Tue, 16 Apr 2019 09:13:47 -0700, Dan Smith <dms at danplanet.com> wrote:
> >> 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.
> The latest incarnation of the quota usage from placement work [1] has
> counting from placement as opt-in, based on a few reasons explained in
> the commit message. And the spec will be amended when/if there is
> confirmation the patches will land in this form.
> Given the opt-in nature of the quota stuff ^, it could be tempting to
> punt it. But my biased opinion is that it would be nice to get working
> on it so we can make counting quota usage from placement our default
> behavior sooner than later.

> Consumer types would enable us to count instances from placement, I
> believe. Current code [1] has to count instances from instance mappings
> in the API database. Consumer types would also enable us to implement
> the quota usage behavior we want during a resize, to take max('instance'
> usage, 'migration' usage).
> Finally, resource provider partitioning would allow quota usage from
> placement to be correct in an environment with multiple nova deployments
> sharing a single placement deployment.
> If we are able to fill in those gaps, we would be in a good position to
> make counting quota usage from placement our default behavior in nova.
I agree that while we have started the quota counting from placement as an
opt-in it would be good to get the missing pieces in to make it whole asap.
I can offer help if needed for the pieces.


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