Wangda Tan commented on YARN-3510:

I think priorities among applications is not supported in YARN now. You cannot 
say app1's priority=10 is less important than app2's priority=5. Application 
priority (YARN-1963) is different. 

IMO, preemption should try to archive the exactly goal of allocation, not more 
than that. Currently allocation doesn't support priorities across application, 
so we shouldn't do that in preemption, otherwise people may ask question like 
"why my container get preempted".

> Create an extension of ProportionalCapacityPreemptionPolicy which preempts a 
> number of containers from each application in a way which respects fairness
> --------------------------------------------------------------------------------------------------------------------------------------------------------
>                 Key: YARN-3510
>                 URL: https://issues.apache.org/jira/browse/YARN-3510
>             Project: Hadoop YARN
>          Issue Type: Sub-task
>          Components: yarn
>            Reporter: Craig Welch
>            Assignee: Craig Welch
>         Attachments: YARN-3510.2.patch, YARN-3510.3.patch, YARN-3510.5.patch, 
> YARN-3510.6.patch
> The ProportionalCapacityPreemptionPolicy preempts as many containers from 
> applications as it can during it's preemption run.  For fifo this makes 
> sense, as it is prempting in reverse order & therefore maintaining the 
> primacy of the "oldest".  For fair ordering this does not have the desired 
> effect - instead, it should preempt a number of containers from each 
> application which maintains a fair balance /close to a fair balance between 
> them

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