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Merge pull request #27754 from shannonxtreme/preemption-qos 

Clarify use of QoS in eviction ranking
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Kubernetes Prow Robot 2021-04-28 12:50:50 -07:00 committed by GitHub
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content/en/docs/concepts/configuration/pod-priority-preemption.md
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@ -353,13 +353,15 @@ the removal of the lowest priority Pods is not sufficient to allow the scheduler
to schedule the preemptor Pod, or if the lowest priority Pods are protected by
`PodDisruptionBudget`.
The only component that considers both QoS and Pod priority is
[kubelet out-of-resource eviction](/docs/tasks/administer-cluster/out-of-resource/).
The kubelet ranks Pods for eviction first by whether or not their usage of the
starved resource exceeds requests, then by Priority, and then by the consumption
of the starved compute resource relative to the Pods' scheduling requests.
See
[evicting end-user pods](/docs/tasks/administer-cluster/out-of-resource/#evicting-end-user-pods)
The kubelet uses Priority to determine pod order for [out-of-resource eviction](/docs/tasks/administer-cluster/out-of-resource/).
You can use the QoS class to estimate the order in which pods are most likely
to get evicted. The kubelet ranks pods for eviction based on the following factors:
1. Whether the starved resource usage exceeds requests
1. Pod Priority
1. Amount of resource usage relative to requests
See [evicting end-user pods](/docs/tasks/administer-cluster/out-of-resource/#evicting-end-user-pods)
for more details.
kubelet out-of-resource eviction does not evict Pods when their
@ -367,7 +369,6 @@ usage does not exceed their requests. If a Pod with lower priority is not
exceeding its requests, it won't be evicted. Another Pod with higher priority
that exceeds its requests may be evicted.
## {{% heading "whatsnext" %}}
* Read about using ResourceQuotas in connection with PriorityClasses: [limit Priority Class consumption by default](/docs/concepts/policy/resource-quotas/#limit-priority-class-consumption-by-default)