Wangda Tan commented on YARN-2009:


Existing user-limit is computed by following logic:
user_limit = min { 
                    max{ current_capacity / #active_users, current_capacity * 
                    queue_capacity * user_limit_factor}

In my above example, the #active_users is 2 instead of 3 (because B has no more 
pending resource). The reason why it uses #active-user is: existing user-limit 
is used to balance *available resource to active users*, it doesn't consider 
the needs to re-balance (via preemption) usages of users. To make intra-queue 
user limit preemption can correctly balance usages between users, we need to 
fix the scheduling logic as well.

> Priority support for preemption in ProportionalCapacityPreemptionPolicy
> -----------------------------------------------------------------------
>                 Key: YARN-2009
>                 URL: https://issues.apache.org/jira/browse/YARN-2009
>             Project: Hadoop YARN
>          Issue Type: Sub-task
>          Components: capacityscheduler
>            Reporter: Devaraj K
>            Assignee: Sunil G
>         Attachments: YARN-2009.0001.patch, YARN-2009.0002.patch
> While preempting containers based on the queue ideal assignment, we may need 
> to consider preempting the low priority application containers first.

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