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https://issues.apache.org/jira/browse/YARN-3655?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14558428#comment-14558428
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zhihai xu commented on YARN-3655:
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Hi [~kasha], thanks for the review.
bq. 1. okToUnreserve
fixed in the new patch YARN-3655.003.patch
bq. 2. Add an if (isValidReservation) check in FSAppAttempt#reserve so all the
reservation logic stays in one place?
IMHO, It is not good to add if (isValidReservation) check in
FSAppAttempt#reserve because all the conditions checked in isValidReservation
are already checked before we call FSAppAttempt#reserve, it will be duplicate
code which will affect the performance.
bq. 3.In {{FSAppAttempt#assignContainer(node, request, nodeType, reserved)}}...
fixed in the new patch YARN-3655.003.patch, In order to remove fitsInMaxShare
check, I merged {{fitsInMaxShare}} check into {{hasContainerForNode}}, which
also make the code cleaner.
bq. 4. 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?
It looks like assignReservedContainer won't lead to a
reservation({{FSAppAttempt#reserve}}), assignReservedContainer won't call
{{FSAppAttempt#reserve}} because {{FSAppAttempt#reserve}} will only be called
when the node Available Resource is smaller than the requested/reserved
resource. assignReservedContainer will only call assignContainer when the node
Available Resource is no less than the reserved resource. So only
{{FSAppAttempt#assignContainer(node)}} can lead to a reservation when the node
Available Resource is smaller than the requested resource.
bq. 5. Instead of calling okToUnreserve/!isValidReservation in
FairScheduler#attemptScheduling...
fixed in the new patch YARN-3655.003.patch
bq. 6. 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?
I suppose you mean assign-multiple is broken after assignReservedContainer
turns the reservation into an allocation.
Yes, I created YARN-3710 to fix this issue.
bq. Oh, and I found it hard to understand the test....
fixed in the new patch YARN-3655.003.patch, please review it.
> 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, YARN-3655.003.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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