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https://issues.apache.org/jira/browse/YARN-9041?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16694329#comment-16694329
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Steven Rand commented on YARN-9041:
-----------------------------------
I'm not sure that this is correct. I think that it can lead to failure to
preempt in cases where we should be preempting. This will happen if the initial
{{potentialNodes}} contain preemptible containers, but the remaining nodes
don't.
Example to illustrate what I'm thinking:
* We have nodes A, B, and C
* At first {{potentialNodes}} includes only node A because we're preempting for
a node-local request for that node
* We find that we can preempt a container on node A, but it's an
ApplicationMaster
* With this patch, we change the search space to be only nodes B and C (without
the patch, the search space becomes A, B, and C)
* There are no preemptible containers on nodes B and C
The outcome in this example is that we don't preempt at all. However, what we
want to do is preempt the AM container on node A.
Hopefully that makes sense, but let me know if I'm misunderstanding.
> Optimize FSPreemptionThread#identifyContainersToPreempt method
> --------------------------------------------------------------
>
> Key: YARN-9041
> URL: https://issues.apache.org/jira/browse/YARN-9041
> Project: Hadoop YARN
> Issue Type: Improvement
> Components: scheduler preemption
> Reporter: Wanqiang Ji
> Assignee: Wanqiang Ji
> Priority: Major
> Attachments: YARN-9041.001.patch
>
>
> In FSPreemptionThread#identifyContainersToPreempt method, I suggest if AM
> preemption, and locality relaxation is allowed, then the search space is
> expanded to all nodes changed to the remaining nodes. The remaining nodes are
> equal to all nodes minus the potential nodes.
> Judging condition changed to:
> # rr.getRelaxLocality()
> # !ResourceRequest.isAnyLocation(rr.getResourceName())
> # bestContainers != null
> # bestContainers.numAMContainers > 0
> If I understand the deviation, please criticize me. thx~
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