Meng Zhu created MESOS-9691:
-------------------------------
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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