Steven Rand created YARN-7290: --------------------------------- Summary: canContainerBePreempted can return true when it shouldn't Key: YARN-7290 URL: https://issues.apache.org/jira/browse/YARN-7290 Project: Hadoop YARN Issue Type: Bug Components: fairscheduler Affects Versions: 3.0.0-beta1 Reporter: Steven Rand
In FSAppAttempt#canContainerBePreempted, we make sure that preempting the given container would not put the app below its fair share: {code} // Check if the app's allocation will be over its fairshare even // after preempting this container Resource usageAfterPreemption = Resources.clone(getResourceUsage()); // Subtract resources of containers already queued for preemption synchronized (preemptionVariablesLock) { Resources.subtractFrom(usageAfterPreemption, resourcesToBePreempted); } // Subtract this container's allocation to compute usage after preemption Resources.subtractFrom( usageAfterPreemption, container.getAllocatedResource()); return !isUsageBelowShare(usageAfterPreemption, getFairShare()); {code} However, this only considers one container in isolation, and fails to consider containers for the same app that we already added to {{preemptableContainers}} in FSPreemptionThread#identifyContainersToPreemptOnNode. Therefore we can have a case where we preempt multiple containers from the same app, none of which by itself puts the app below fair share, but which cumulatively do so. I've attached a patch with a test to show this behavior. The flow is: 1. Initially greedyApp runs in {{root.preemptable.child-1}} and is allocated all the resources (8g and 8vcores) 2. Then starvingApp runs in {{root.preemptable.child-2}} and requests 2 containers, each of which is 3g and 3vcores in size. At this point both greedyApp and starvingApp have a fair share of 4g (with DRF not in use). 3. For the first container requested by starvedApp, we (correctly) preempt 3 containers from greedyApp, each of which is 1g and 1vcore. 4. For the second container requested by starvedApp, we again (this time incorrectly) preempt 3 containers from greedyApp. This puts greedyApp below its fair share, but happens anyway because all six times that we call {{return !isUsageBelowShare(usageAfterPreemption, getFairShare());}}, the value of {{usageAfterPreemption}} is 7g and 7vcores (confirmed using debugger). So in addition to accounting for {{resourcesToBePreempted}}, we also need to account for containers that we're already planning on preempting in FSPreemptionThread#identifyContainersToPreemptOnNode. -- This message was sent by Atlassian JIRA (v6.4.14#64029) --------------------------------------------------------------------- To unsubscribe, e-mail: yarn-issues-unsubscr...@hadoop.apache.org For additional commands, e-mail: yarn-issues-h...@hadoop.apache.org