Public bug reported: Some virt drivers report additional overhead per instance for memory and disk usage on a compute node. That is not reported in the allocations records for a given instance on a resource provider (compute node), however:
https://github.com/openstack/nova/blob/15.0.0/nova/scheduler/client/report.py#L157 It is used as part of the claim test on the compute when creating an instance or moving an instance. For creating an instance, that's done here: https://github.com/openstack/nova/blob/15.0.0/nova/compute/resource_tracker.py#L144-L156 https://github.com/openstack/nova/blob/15.0.0/nova/compute/claims.py#L165 Where Claim.memory_mb is the instance.flavor.memory_mb + overhead: https://github.com/openstack/nova/blob/15.0.0/nova/compute/claims.py#L106 So ultimately what we claim on the compute node is not what we report to placement for allocations for that instance. This matters because when the filter scheduler is asking placement for a list of resource providers that can fit a given request memory_mb and disk_gb it relies on the inventory for the compute node resource provider and the existing usage (allocations) for that provider, and we aren't reporting the full story to placement. This could lead to placement telling the filter scheduler there is room to place an instance on a given compute node when in fact that could fail the claim once we get to the host, which would results in a retry of the build on another host (which can be expensive). Also, when we start having multi-cell support with a top-level conductor that the computes can't reach, we won't have build retries anymore, so you'd just fail the claim and the build would be done and the instance would go to ERROR state. So it's critical that the placement service has the proper information for making the correct decision on the first try. ** Affects: nova Importance: High Status: Triaged ** Tags: placement resource-tracker scheduler -- You received this bug notification because you are a member of Yahoo! Engineering Team, which is subscribed to OpenStack Compute (nova). https://bugs.launchpad.net/bugs/1683858 Title: Allocation records do not contain overhead information Status in OpenStack Compute (nova): Triaged Bug description: Some virt drivers report additional overhead per instance for memory and disk usage on a compute node. That is not reported in the allocations records for a given instance on a resource provider (compute node), however: https://github.com/openstack/nova/blob/15.0.0/nova/scheduler/client/report.py#L157 It is used as part of the claim test on the compute when creating an instance or moving an instance. For creating an instance, that's done here: https://github.com/openstack/nova/blob/15.0.0/nova/compute/resource_tracker.py#L144-L156 https://github.com/openstack/nova/blob/15.0.0/nova/compute/claims.py#L165 Where Claim.memory_mb is the instance.flavor.memory_mb + overhead: https://github.com/openstack/nova/blob/15.0.0/nova/compute/claims.py#L106 So ultimately what we claim on the compute node is not what we report to placement for allocations for that instance. This matters because when the filter scheduler is asking placement for a list of resource providers that can fit a given request memory_mb and disk_gb it relies on the inventory for the compute node resource provider and the existing usage (allocations) for that provider, and we aren't reporting the full story to placement. This could lead to placement telling the filter scheduler there is room to place an instance on a given compute node when in fact that could fail the claim once we get to the host, which would results in a retry of the build on another host (which can be expensive). Also, when we start having multi-cell support with a top-level conductor that the computes can't reach, we won't have build retries anymore, so you'd just fail the claim and the build would be done and the instance would go to ERROR state. So it's critical that the placement service has the proper information for making the correct decision on the first try. To manage notifications about this bug go to: https://bugs.launchpad.net/nova/+bug/1683858/+subscriptions -- Mailing list: https://launchpad.net/~yahoo-eng-team Post to : [email protected] Unsubscribe : https://launchpad.net/~yahoo-eng-team More help : https://help.launchpad.net/ListHelp
