Alexander Rukletsov created MESOS-4441:
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Summary: Do not allocate non-revocable resources beyond quota
guarantee.
Key: MESOS-4441
URL: https://issues.apache.org/jira/browse/MESOS-4441
Project: Mesos
Issue Type: Improvement
Components: allocation
Reporter: Alexander Rukletsov
Assignee: Alexander Rukletsov
Priority: Blocker
h4. Status quo
Currently resources allocated to frameworks in a role with quota (aka quota'ed
role) beyond quota guarantee are marked non-revocable. This impacts our
flexibility for revoking them if we decide so in the future.
h4. Proposal
Once quota guarantee is satisfied we must not necessarily further allocate
resources as non-revocable. Instead we can mark all offers resources beyond
guarantee as revocable. When in the future {{RevocableInfo}} evolves frameworks
will get additional information about "revocability" of the resource (i.e.
allocation slack)
h4. Caveats
Though it seems like a simple change, it has several implications.
h6. Fairness
Currently the hierarchical allocator considers revocable resources as regular
resources when doing fairness calculations. This may prevent frameworks getting
non-revocable resources as part of their role's quota guarantee if they accept
some revocable resources as well.
Consider the following scenario. A single framework in a role with quota set to
{{10}} CPUs is allocated {{10}} CPUs as non-revocable resources as part of its
quota and additionally {{2}} revocable CPUs. Now a task using {{2}}
non-revocable CPUs finishes and its resources are returned. Total allocation
for the role is {{8}} non-revocable + {{2}} revocable. However, the role may
not be offered additional {{2}} non-revocable since its total allocation
satisfies quota.
h6. Coarse-grained nature of allocation
The hierarchical allocator performs "coarse-grained" allocation, meaning it
always allocates the entire remaining agent resources to a single framework.
This may lead to over-allocating some resources as non-revocable beyond quota
guarantee.
h6. Quotas smaller than fair share
If a quota set for a role is smaller than its fair share, it may reduce the
amount of resources offered to this role, if frameworks in it do not accept
revocable resources. This is probably the most important consequence of the
proposed change. Operators may set quota to get guarantees, but may observe a
decrease in amount of resources a role gets, which is not intuitive.
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