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https://issues.apache.org/jira/browse/YUNIKORN-3442?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Manikandan R resolved YUNIKORN-3442.
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Fix Version/s: 1.11.0
Resolution: Fixed
> [Core] Preemptor ask may never be scheduled when encountering pod
> anti-affinity
> -------------------------------------------------------------------------------
>
> Key: YUNIKORN-3442
> URL: https://issues.apache.org/jira/browse/YUNIKORN-3442
> Project: Apache YuniKorn
> Issue Type: Bug
> Components: core - scheduler
> Affects Versions: 1.6.0
> Reporter: Hedger Lai
> Assignee: Hedger Lai
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.11.0
>
>
> h3. Problem
> When preemption is triggered, the K8s shim evaluates predicate plugins (such
> as PodAntiAffinity or TopologySpreadConstraints) and returns a specific list
> of victim pods that must be removed for the preemptor to fit on the node.
> However, in Core's {{TryPreemption()}}
> ({{pkg/scheduler/objects/preemption.go#L650-L663}}), the scheduler does not
> honor this finalized victim list. Instead, it iterates through the victims
> and only collects allocations that contribute to unsatisfied resource
> dimensions of the ask:
> {code:go}
> for k, needVal := range p.ask.GetAllocatedResource().Resources {
> if victimsTotalResource.Resources[k] < needVal && allocRes.Resources[k] >
> 0 {
> finalVictims = append(finalVictims, victim)
> victimsTotalResource.AddTo(allocRes)
> break
> }
> }
> {code}
> h3. Impact
> This secondary resource-based filtering breaks predicate guarantees.
> Once the ask's CPU/memory demands are satisfied by earlier victims, any
> subsequent victim selected by the Shim solely to resolve a PodAntiAffinity
> constraint is silently dropped by the Core.
> As a result:
> # Innocent victims are evicted unnecessarily without allowing the preemptor
> to schedule.
> # The preemptor still fails predicate checks in subsequent scheduling cycles
> because the anti-affinity culprit pod remains on the node.
> # Preemption triggers repeatedly for the same ask, leading to victim eviction
> churn and preemption livelock.
> h3. Proposed Fix
> Core's {{TryPreemption()}} should respect the victim list finalized by the
> Shim for the target node and avoid secondary resource-based truncation,
> ensuring predicate conditions verified by the Shim remain intact.
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