[jira] [Created] (MESOS-9691) Quota headroom calculation is off when subroles are involved.

["Meng Zhu (JIRA)" <ji...@apache.org>]

Meng Zhu created MESOS-9691:
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             Summary: Quota headroom calculation is off when subroles are involved.
                 Key: MESOS-9691
                 URL: https://issues.apache.org/jira/browse/MESOS-9691
             Project: Mesos
          Issue Type: Bug
          Components: allocation
            Reporter: Meng Zhu


Quota "availableHeadroom" calculation:

https://github.com/apache/mesos/blob/6276f7e73b0dbe7df49a7315cd1b83340d66f4ea/src/master/allocator/mesos/hierarchical.cpp#L1751-L1754

is off when subroles are involved.

Specifically, in the formula 
{noformat}
available headroom = total resources - allocated resources - (total reservations - allocated reservations) - unallocated revocable resources
{noformat}

The "allocated resources" part is hierarchical-aware and aggregate that across all roles, thus allocations to subroles will be counted multiple times (in the case of "a/b", once for "a" and once for "a/b").

The "total reservations"  is correct, since today it is "flat" (reservations made to "a/b" are not counted to "a"). Thus all reservations are only counted once -- which is the correct semantic here. However, once we fix MESOS-9688 (which likely requires reservation tracking to be hierarchical-aware), we need to ensure that the accounting is still correct.

The "allocated reservations" is hierarchical-aware, thus overlap accounting would occur.

Basically, when calculating the available headroom, we need to ensure "single-counting". Ideally, we only need to look at the root's consumptions.





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