Meng Zhu created MESOS-8339:
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Summary: Quota headroom may be insufficiently held when role has
more reservation than quota.
Key: MESOS-8339
URL: https://issues.apache.org/jira/browse/MESOS-8339
Project: Mesos
Issue Type: Bug
Components: allocation
Reporter: Meng Zhu
If a role has more reservation than its quota, the current quota headroom
calculation is insufficient in guaranteeing quota allocation.
Consider, role `A` with 100 (units of resource, same below) reservation and 10
quota and role `B` with no reservation and 90 quota. Let's say there is no
allocation yet. The existing allocator would calculate that the required
headroom is 100. And since unallocated quota role reserved resource is also
100, no additional resources would be held back for the headroom.
While role `A` would have no problem getting its quota satisfied. Role `B` may
have difficulty getting any resources because the "headroom" can only be
allocated to `A`.
The solution is to calculate per-role headroom before aggregating the quantity.
And unallocated reservations should not count towards quota headroom. In the
above case. The headroom for role `A` should be zero, the headroom for role `B`
should be 90. Thus the aggregated headroom will be `90`.
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