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https://issues.apache.org/jira/browse/YARN-3655?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14557003#comment-14557003
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Karthik Kambatla commented on YARN-3655:
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Comments on the patch:
# okToUnreserve
## It was a little hard to wrap my head around. Can we negate it and call it
{{isValidReservation(FSSchedulerNode)}}?
## Can we get rid of the if-else and have a simple {{return hasContainerForNode
&& fitsInMaxShare && !isOverAMShareLimit}}?
# Add an {{if (isValidReservation)}} check in {{FSAppAttempt#reserve}} so all
the reservation logic stays in one place?
# In {{FSAppAttempt#assignContainer(node, request, nodeType, reserved)}},
## We can get rid of the fitsInMaxShare check immediately preceding the call to
{{reserve}}.
## Given {{if (fitsIn(capability, available))}}-block ends in return, we don't
need to put the continuation in else.
# While adding this check in {{FSAppAttempt#assignContainer(node)}} might work
in practice, it somehow feels out of place. Also, assignReservedContainer could
also lead to a reservation?
# Instead of calling {{okToUnreserve}}/{{!isValidReservation}} in
{{FairScheduler#attemptScheduling}}, we should likely add it as the first check
in {{FSAppAttempt#assignReservedContainer}}.
# Looks like assign-multiple is broken with reserved-containers. The while-loop
for assign-multiple should look at both reserved and un-reserved containers
assigned. Can we file a follow-up JIRA to fix this?
> FairScheduler: potential livelock due to maxAMShare limitation and container
> reservation
> -----------------------------------------------------------------------------------------
>
> Key: YARN-3655
> URL: https://issues.apache.org/jira/browse/YARN-3655
> Project: Hadoop YARN
> Issue Type: Bug
> Components: fairscheduler
> Affects Versions: 2.7.0
> Reporter: zhihai xu
> Assignee: zhihai xu
> Attachments: YARN-3655.000.patch, YARN-3655.001.patch,
> YARN-3655.002.patch
>
>
> FairScheduler: potential livelock due to maxAMShare limitation and container
> reservation.
> If a node is reserved by an application, all the other applications don't
> have any chance to assign a new container on this node, unless the
> application which reserves the node assigns a new container on this node or
> releases the reserved container on this node.
> The problem is if an application tries to call assignReservedContainer and
> fail to get a new container due to maxAMShare limitation, it will block all
> other applications to use the nodes it reserves. If all other running
> applications can't release their AM containers due to being blocked by these
> reserved containers. A livelock situation can happen.
> The following is the code at FSAppAttempt#assignContainer which can cause
> this potential livelock.
> {code}
> // Check the AM resource usage for the leaf queue
> if (!isAmRunning() && !getUnmanagedAM()) {
> List<ResourceRequest> ask = appSchedulingInfo.getAllResourceRequests();
> if (ask.isEmpty() || !getQueue().canRunAppAM(
> ask.get(0).getCapability())) {
> if (LOG.isDebugEnabled()) {
> LOG.debug("Skipping allocation because maxAMShare limit would " +
> "be exceeded");
> }
> return Resources.none();
> }
> }
> {code}
> To fix this issue, we can unreserve the node if we can't allocate the AM
> container on the node due to Max AM share limitation and the node is reserved
> by the application.
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