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https://issues.apache.org/jira/browse/MESOS-5741?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Benjamin Mahler updated MESOS-5741:
-----------------------------------
Labels: mesosphere multitenancy (was: mesosphere)
> Quota + reserved resources is overly conservative
> -------------------------------------------------
>
> Key: MESOS-5741
> URL: https://issues.apache.org/jira/browse/MESOS-5741
> Project: Mesos
> Issue Type: Bug
> Reporter: Neil Conway
> Labels: mesosphere, multitenancy
>
> Consider this scenario:
> * Cluster has 10 CPUs total. 8 CPUs are reserved for role X, 2 CPUs are
> unreserved.
> * Role X has a quota for 4 CPUs, but has only been allocated 2 CPUs (e.g.,
> because it has declined an offer for the other 2 CPUs). The CPUs it has been
> allocated come from the reserved resources, so there are 6 reserved CPUs and
> 2 unreserved CPUs available.
> * That means 6 CPUs should be offered as non-quota resources. However, which
> 6 CPUs should be offered -- the 6 reserved CPUs, or 4 reserved CPUs and 2
> unreserved CPUs?
> The current quota allocation logic appears to always offer the 6 reserved
> CPUs. This is unfortunate, because frameworks in other roles won't be able to
> use those resources. The reason for this behavior is:
> {code}
> Resources remainingClusterResources = roleSorter->totalScalarQuantities();
> foreachkey (const string& role, activeRoles) {
> remainingClusterResources -= roleSorter->allocationScalarQuantities(role);
> }
> {code}
> {{remainingClusterResources}} may have a {{role}} set (although dynamically
> reserved resources will have been converted into effectively static
> reservations).
> {code}
> Resources unallocatedQuotaResources;
> foreachpair (const string& name, const Quota& quota, quotas) {
> // Compute the amount of quota that the role does not have allocated.
> //
> // NOTE: Revocable resources are excluded in `quotaRoleSorter`.
> // NOTE: Only scalars are considered for quota.
> Resources allocated = getQuotaRoleAllocatedResources(name);
> const Resources required = quota.info.guarantee();
> unallocatedQuotaResources += (required - allocated);
> }
> {code}
> {{unallocatedQuotaResources}} will *not* have {{role}} set, per the
> implementation of {{getQuotaRoleAllocatedResources}}.
> {code}
> remainingClusterResources -= unallocatedQuotaResources;
> {code}
> This means that *only* unreserved resources will be subtracted from
> {{remainingClusterResources}}. At best this is sub-optimal, because it seems
> better to lay-away resources for role X that are already reserved for X. I
> don't *think* it will result in violating quota guarantees, though.
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