[ 
https://issues.apache.org/jira/browse/YARN-6151?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15856917#comment-15856917
 ] 

ASF GitHub Bot commented on YARN-6151:
--------------------------------------

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

    https://github.com/apache/hadoop/pull/188#discussion_r99943541
  
    --- Diff: 
hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/TestFairScheduler.java
 ---
    @@ -2036,10 +2036,10 @@ public void testPreemptionIsNotDelayedToNextRound() 
throws Exception {
                 .getLeafQueue("queueA.queueA2", false), clock.getTime());
         assertEquals(3277, toPreempt.getMemorySize());
     
    -    // verify if the 3 containers required by queueA2 are preempted in the 
same
    +    // verify if the 4 containers required by queueA2 are preempted in the 
same
         // round
         scheduler.preemptResources(toPreempt);
    -    assertEquals(3, 
scheduler.getSchedulerApp(app1).getPreemptionContainers()
    +    assertEquals(4, 
scheduler.getSchedulerApp(app1).getPreemptionContainers()
             .size());
       }
    --- End diff --
    
    Can we add a new test that verifies the exact scenario in the JIRA 
description? 


> FS Preemption doesn't filter out queues which cannot be preempted
> -----------------------------------------------------------------
>
>                 Key: YARN-6151
>                 URL: https://issues.apache.org/jira/browse/YARN-6151
>             Project: Hadoop YARN
>          Issue Type: Bug
>          Components: fairscheduler
>    Affects Versions: 2.8.0
>            Reporter: Yufei Gu
>            Assignee: Yufei Gu
>         Attachments: YARN-6151.branch-2.8.001.patch
>
>
> This is preemption bug happens before 2.8.0, which also described in 
> YARN-3405.
> Queue hierarchy described as below:
> {noformat}
>                   root
>                /         \
>        queue-1          queue-2       
>           /      \
> queue-1-1     queue-1-2
> {noformat}
> Assume cluster resource is 100 and all queues have same weights.
> # queue-1-1 and queue-2 has apps. Each get 50 usage and 50 fairshare. 
> # When queue-1-2 is active, supposedly it will preempt 25 from queue-1-1, but 
> this doesn't happen because preemption happens top-down, queue-2 could be the 
> preemption candidate as long as queue-2 is less needy than queue-1, and 
> queue-2 doesn't exceed the fair share which means preemption won't happen.
> We need to filter out queue-2 since it isn't a valid candidate.



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