Ashwin Shankar created YARN-3453:

             Summary: Fair Scheduler : Parts of preemption logic uses 
DefaultResourceCalculator even in DRF mode causing thrashing
                 Key: YARN-3453
             Project: Hadoop YARN
          Issue Type: Bug
          Components: fairscheduler
    Affects Versions: 2.6.0
            Reporter: Ashwin Shankar

There are two places in preemption code flow where DefaultResourceCalculator is 
used, even in DRF mode.
Which basically results in more resources getting preempted than needed, and 
those extra preempted containers aren’t even getting to the “starved” queue 
since scheduling logic is based on DRF's Calculator.

Following are the two places :
1. {|borderStyle=solid}
private boolean isStarved(Resource share)
A queue shouldn’t be marked as “starved” if the dominant resource usage
is >=  fair/minshare.

2. {|borderStyle=solid}
protected Resource resToPreempt(FSLeafQueue sched, long curTime)

One more thing that I believe needs to change in DRF mode is : during a 
preemption round,if preempting a few containers results in satisfying needs of 
a resource type, then we should exit that preemption round, since the 
containers that we just preempted should bring the dominant resource usage to 
min/fair share.

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