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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 Mon, 13 Mar 2017 23:00:43 GMT

    [ https://issues.apache.org/jira/browse/YARN-5829?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15923135#comment-15923135
] 

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

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

    https://github.com/apache/hadoop/pull/201#discussion_r105785747
  
    --- Diff: hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/FSAppAttempt.java
---
    @@ -831,7 +831,11 @@ private Resource assignContainer(
         }
     
         // The desired container won't fit here, so reserve
    -    if (isReservable(capability) &&
    +    // Important: Do not enable this kind of reservation in case of preemption,
    +    // since the preempted application will re-reserve the preempted resources
    +    // and prevent the starving application to get them
    +    if (!scheduler.getConf().getPreemptionEnabled() &&
    --- End diff --
    
    This seems very bad. What happens if preemption is enabled, but no containers are preempted.
However, if there are apps requesting large containers that don't fit in the free resources
created by smaller containers finishing, these apps end up being starved forever. 


> 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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