filterout those nodes which are not helpful for preemptation

[lowang-bh]

What would you like to be added:

like K8s preemptations, it first filters out those nodes will not help preemption

https://github.com/kubernetes/kubernetes/blob/dbcbf5e952266479df92c84457781c0a2a688afd/pkg/scheduler/framework/preemption/preemption.go#L223C2-L239

        potentialNodes, unschedulableNodeStatus := nodesWherePreemptionMightHelp(allNodes, m)
        if len(potentialNodes) == 0 {
                logger.V(3).Info("Preemption will not help schedule pod on any node", "pod", klog.KObj(pod))
                // In this case, we should clean-up any existing nominated node name of the pod.
                if err := util.ClearNominatedNodeName(ctx, ev.Handler.ClientSet(), pod); err != nil {
                        logger.Error(err, "Could not clear the nominatedNodeName field of pod", "pod", klog.KObj(pod))
                        // We do not return as this error is not critical.
                }
                return nil, unschedulableNodeStatus, nil
        }


        pdbs, err := getPodDisruptionBudgets(ev.PdbLister)
        if err != nil {
                return nil, nil, err
        }


        offset, numCandidates := ev.GetOffsetAndNumCandidates(int32(len(potentialNodes)))

https://github.com/kubernetes/kubernetes/blob/dbcbf5e952266479df92c84457781c0a2a688afd/pkg/scheduler/framework/preemption/preemption.go#L413-L428

// nodesWherePreemptionMightHelp returns a list of nodes with failed predicates
// that may be satisfied by removing pods from the node.
func nodesWherePreemptionMightHelp(nodes []*framework.NodeInfo, m framework.NodeToStatusMap) ([]*framework.NodeInfo, framework.NodeToStatusMap) {
        var potentialNodes []*framework.NodeInfo
        nodeStatuses := make(framework.NodeToStatusMap)
        for _, node := range nodes {
                name := node.Node().Name
                // We rely on the status by each plugin - 'Unschedulable' or 'UnschedulableAndUnresolvable'
                // to determine whether preemption may help or not on the node.
                if m[name].Code() == framework.UnschedulableAndUnresolvable {
                        nodeStatuses[node.Node().Name] = framework.NewStatus(framework.UnschedulableAndUnresolvable, "Preemption is not helpful for scheduling")
                        continue
                }
                potentialNodes = append(potentialNodes, node)
        }
        return potentialNodes, nodeStatuses
}

Why is this needed:

reduce the nodes which need to run filter on them

[tanberBro]

Which nodes should be filtered first? Unscheduled and unknown?
@lowang-bh