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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-5829) FS preemption should reserve a node before considering containers on it for preemption
Date Fri, 24 Mar 2017 01:38:41 GMT

    [ https://issues.apache.org/jira/browse/YARN-5829?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15939544#comment-15939544
] 

ASF GitHub Bot commented on YARN-5829:
--------------------------------------

Github user szegedim commented on a diff in the pull request:

    https://github.com/apache/hadoop/pull/201#discussion_r107820670
  
    --- Diff: hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/FairScheduler.java
---
    @@ -987,9 +978,19 @@ void attemptScheduling(FSSchedulerNode node) {
           }
     
           // Assign new containers...
    -      // 1. Check for reserved applications
    -      // 2. Schedule if there are no reservations
    -
    +      // 1. Ensure containers are assigned to the apps that preempted
    +      // 2. Check for reserved applications
    +      // 3. Schedule if there are no reservations
    +
    +      // Apps may wait for preempted containers
    +      // We have to satisfy these first to avoid cases, when we preempt
    +      // a container for A from B and C gets the preempted containers,
    +      // when C does not qualify for preemption itself.
    +      for (FSAppAttempt app : node.getPreemptionList()) {
    --- End diff --
    
    > Would it help to store the apps in a TreeMap in FSSchedulerNode and have a method
that > returns the next preempted app to allocate to? If none exist, return null? Also,
if this were > to work, we might have to revert back to the behavior in an earlier patch:
add app/resources to the map only after the container is actually preempted?
    This approach has a clear advantage, that it allocates any newly appeared container to
the preemptors. TreeMap might slow down search a little bit. Let's try to continue with this
approach but multiple allocations enabled.


> FS preemption should reserve a node before considering containers on it for preemption
> --------------------------------------------------------------------------------------
>
>                 Key: YARN-5829
>                 URL: https://issues.apache.org/jira/browse/YARN-5829
>             Project: Hadoop YARN
>          Issue Type: Sub-task
>          Components: fairscheduler
>            Reporter: Karthik Kambatla
>            Assignee: Miklos Szegedi
>
> FS preemption evaluates nodes for preemption, and subsequently preempts identified containers.
If this node is not reserved for a specific application, any other application could be allocated
resources on this node. 
> Reserving the node for the starved application before preempting containers would help
avoid this.



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