lownodeutilization: evictionLimits to limit the evictions per plugin

In some cases it might be usefull to limit how many evictions per a
domain can be performed. To avoid burning the whole per descheduling
cycle budget. Limiting the number of evictions per node is a
prerequisite for evicting pods whose usage can't be easily subtracted
from overall node resource usage to predict the final usage. E.g. when a
pod is evicted due to high PSI pressure which takes into account many
factors which can be fully captured by the current predictive resource
model.

pkg/framework/plugins/nodeutilization/highnodeutilization.go

@@ -161,6 +161,7 @@ func (h *HighNodeUtilization) Balance(ctx context.Context, nodes []*v1.Node) *fr
 		h.resourceNames,
 		continueEvictionCond,
 		h.usageClient,
+		nil,
 	)
 
 	return nil

pkg/framework/plugins/nodeutilization/lownodeutilization.go

@@ -183,6 +183,11 @@ func (l *LowNodeUtilization) Balance(ctx context.Context, nodes []*v1.Node) *fra
 	// Sort the nodes by the usage in descending order
 	sortNodesByUsage(sourceNodes, false)
 
+	var nodeLimit *uint
+	if l.args.EvictionLimits != nil {
+		nodeLimit = l.args.EvictionLimits.Node
+	}
+
 	evictPodsFromSourceNodes(
 		ctx,
 		l.args.EvictableNamespaces,
@@ -194,6 +199,7 @@ func (l *LowNodeUtilization) Balance(ctx context.Context, nodes []*v1.Node) *fra
 		l.resourceNames,
 		continueEvictionCond,
 		l.usageClient,
+		nodeLimit,
 	)
 
 	return nil

pkg/framework/plugins/nodeutilization/lownodeutilization_test.go

@@ -31,6 +31,7 @@ import (
 	core "k8s.io/client-go/testing"
 	"k8s.io/metrics/pkg/apis/metrics/v1beta1"
 	fakemetricsclient "k8s.io/metrics/pkg/client/clientset/versioned/fake"
+	"k8s.io/utils/ptr"
 
 	"sigs.k8s.io/descheduler/pkg/api"
 	"sigs.k8s.io/descheduler/pkg/descheduler/evictions"
@@ -63,6 +64,7 @@ func TestLowNodeUtilization(t *testing.T) {
 		expectedPodsWithMetricsEvicted uint
 		evictedPods                    []string
 		evictableNamespaces            *api.Namespaces
+		evictionLimits                 *api.EvictionLimits
 	}{
 		{
 			name: "no evictable pods",
@@ -1122,6 +1124,72 @@ func TestLowNodeUtilization(t *testing.T) {
 			expectedPodsEvicted:            3,
 			expectedPodsWithMetricsEvicted: 2,
 		},
+		{
+			name: "without priorities with node eviction limit",
+			thresholds: api.ResourceThresholds{
+				v1.ResourceCPU:  30,
+				v1.ResourcePods: 30,
+			},
+			targetThresholds: api.ResourceThresholds{
+				v1.ResourceCPU:  50,
+				v1.ResourcePods: 50,
+			},
+			evictionLimits: &api.EvictionLimits{
+				Node: ptr.To[uint](2),
+			},
+			nodes: []*v1.Node{
+				test.BuildTestNode(n1NodeName, 4000, 3000, 9, nil),
+				test.BuildTestNode(n2NodeName, 4000, 3000, 10, nil),
+				test.BuildTestNode(n3NodeName, 4000, 3000, 10, test.SetNodeUnschedulable),
+			},
+			pods: []*v1.Pod{
+				test.BuildTestPod("p1", 400, 0, n1NodeName, test.SetRSOwnerRef),
+				test.BuildTestPod("p2", 400, 0, n1NodeName, test.SetRSOwnerRef),
+				test.BuildTestPod("p3", 400, 0, n1NodeName, test.SetRSOwnerRef),
+				test.BuildTestPod("p4", 400, 0, n1NodeName, test.SetRSOwnerRef),
+				test.BuildTestPod("p5", 400, 0, n1NodeName, test.SetRSOwnerRef),
+				// These won't be evicted.
+				test.BuildTestPod("p6", 400, 0, n1NodeName, test.SetDSOwnerRef),
+				test.BuildTestPod("p7", 400, 0, n1NodeName, func(pod *v1.Pod) {
+					// A pod with local storage.
+					test.SetNormalOwnerRef(pod)
+					pod.Spec.Volumes = []v1.Volume{
+						{
+							Name: "sample",
+							VolumeSource: v1.VolumeSource{
+								HostPath: &v1.HostPathVolumeSource{Path: "somePath"},
+								EmptyDir: &v1.EmptyDirVolumeSource{
+									SizeLimit: resource.NewQuantity(int64(10), resource.BinarySI),
+								},
+							},
+						},
+					}
+					// A Mirror Pod.
+					pod.Annotations = test.GetMirrorPodAnnotation()
+				}),
+				test.BuildTestPod("p8", 400, 0, n1NodeName, func(pod *v1.Pod) {
+					// A Critical Pod.
+					pod.Namespace = "kube-system"
+					priority := utils.SystemCriticalPriority
+					pod.Spec.Priority = &priority
+				}),
+				test.BuildTestPod("p9", 400, 0, n2NodeName, test.SetRSOwnerRef),
+			},
+			nodemetricses: []*v1beta1.NodeMetrics{
+				test.BuildNodeMetrics(n1NodeName, 3201, 0),
+				test.BuildNodeMetrics(n2NodeName, 401, 0),
+				test.BuildNodeMetrics(n3NodeName, 11, 0),
+			},
+			podmetricses: []*v1beta1.PodMetrics{
+				test.BuildPodMetrics("p1", 401, 0),
+				test.BuildPodMetrics("p2", 401, 0),
+				test.BuildPodMetrics("p3", 401, 0),
+				test.BuildPodMetrics("p4", 401, 0),
+				test.BuildPodMetrics("p5", 401, 0),
+			},
+			expectedPodsEvicted:            2,
+			expectedPodsWithMetricsEvicted: 2,
+		},
 	}
 
 	for _, tc := range testCases {
@@ -1193,6 +1261,7 @@ func TestLowNodeUtilization(t *testing.T) {
 					Thresholds:             tc.thresholds,
 					TargetThresholds:       tc.targetThresholds,
 					UseDeviationThresholds: tc.useDeviationThresholds,
+					EvictionLimits:         tc.evictionLimits,
 					EvictableNamespaces:    tc.evictableNamespaces,
 					MetricsUtilization: MetricsUtilization{
 						MetricsServer: metricsEnabled,

pkg/framework/plugins/nodeutilization/nodeutilization.go

@@ -239,6 +239,7 @@ func evictPodsFromSourceNodes(
 	resourceNames []v1.ResourceName,
 	continueEviction continueEvictionCond,
 	usageClient usageClient,
+	maxNoOfPodsToEvictPerNode *uint,
 ) {
 	// upper bound on total number of pods/cpu/memory and optional extended resources to be moved
 	totalAvailableUsage := api.ReferencedResourceList{}
@@ -280,7 +281,7 @@ func evictPodsFromSourceNodes(
 		klog.V(1).InfoS("Evicting pods based on priority, if they have same priority, they'll be evicted based on QoS tiers")
 		// sort the evictable Pods based on priority. This also sorts them based on QoS. If there are multiple pods with same priority, they are sorted based on QoS tiers.
 		podutil.SortPodsBasedOnPriorityLowToHigh(removablePods)
-		err := evictPods(ctx, evictableNamespaces, removablePods, node, totalAvailableUsage, taintsOfDestinationNodes, podEvictor, evictOptions, continueEviction, usageClient)
+		err := evictPods(ctx, evictableNamespaces, removablePods, node, totalAvailableUsage, taintsOfDestinationNodes, podEvictor, evictOptions, continueEviction, usageClient, maxNoOfPodsToEvictPerNode)
 		if err != nil {
 			switch err.(type) {
 			case *evictions.EvictionTotalLimitError:
@@ -302,14 +303,20 @@ func evictPods(
 	evictOptions evictions.EvictOptions,
 	continueEviction continueEvictionCond,
 	usageClient usageClient,
+	maxNoOfPodsToEvictPerNode *uint,
 ) error {
 	var excludedNamespaces sets.Set[string]
 	if evictableNamespaces != nil {
 		excludedNamespaces = sets.New(evictableNamespaces.Exclude...)
 	}
 
+	var evictionCounter uint = 0
 	if continueEviction(nodeInfo, totalAvailableUsage) {
 		for _, pod := range inputPods {
+			if maxNoOfPodsToEvictPerNode != nil && evictionCounter >= *maxNoOfPodsToEvictPerNode {
+				klog.V(3).InfoS("Max number of evictions per node per plugin reached", "limit", *maxNoOfPodsToEvictPerNode)
+				break
+			}
 			if !utils.PodToleratesTaints(pod, taintsOfLowNodes) {
 				klog.V(3).InfoS("Skipping eviction for pod, doesn't tolerate node taint", "pod", klog.KObj(pod))
 				continue
@@ -334,6 +341,7 @@ func evictPods(
 			}
 			err = podEvictor.Evict(ctx, pod, evictOptions)
 			if err == nil {
+				evictionCounter++
 				klog.V(3).InfoS("Evicted pods", "pod", klog.KObj(pod))
 
 				for name := range totalAvailableUsage {

pkg/framework/plugins/nodeutilization/types.go

@@ -34,6 +34,9 @@ type LowNodeUtilizationArgs struct {
 	// considered while considering resources used by pods
 	// but then filtered out before eviction
 	EvictableNamespaces *api.Namespaces `json:"evictableNamespaces,omitempty"`
+
+	// evictionLimits limits the number of evictions per domain. E.g. node, namespace, total.
+	EvictionLimits *api.EvictionLimits `json:"evictionLimits,omitempty"`
 }
 
 // +k8s:deepcopy-gen=true

pkg/framework/plugins/nodeutilization/zz_generated.deepcopy.go

@@ -88,6 +88,11 @@ func (in *LowNodeUtilizationArgs) DeepCopyInto(out *LowNodeUtilizationArgs) {
 		*out = new(api.Namespaces)
 		(*in).DeepCopyInto(*out)
 	}
+	if in.EvictionLimits != nil {
+		in, out := &in.EvictionLimits, &out.EvictionLimits
+		*out = new(api.EvictionLimits)
+		(*in).DeepCopyInto(*out)
+	}
 	return
 }