Improve slice allocation in LabelSelectorAsSelector

staging/src/k8s.io/apimachinery/pkg/apis/meta/v1/helpers.go

@@ -38,13 +38,13 @@ func LabelSelectorAsSelector(ps *LabelSelector) (labels.Selector, error) {
 	if len(ps.MatchLabels)+len(ps.MatchExpressions) == 0 {
 		return labels.Everything(), nil
 	}
-	selector := labels.NewSelector()
+	requirements := make([]labels.Requirement, 0, len(ps.MatchLabels)+len(ps.MatchExpressions))
 	for k, v := range ps.MatchLabels {
 		r, err := labels.NewRequirement(k, selection.Equals, []string{v})
 		if err != nil {
 			return nil, err
 		}
-		selector = selector.Add(*r)
+		requirements = append(requirements, *r)
 	}
 	for _, expr := range ps.MatchExpressions {
 		var op selection.Operator
@@ -64,8 +64,10 @@ func LabelSelectorAsSelector(ps *LabelSelector) (labels.Selector, error) {
 		if err != nil {
 			return nil, err
 		}
-		selector = selector.Add(*r)
+		requirements = append(requirements, *r)
 	}
+	selector := labels.NewSelector()
+	selector = selector.Add(requirements...)
 	return selector, nil
 }
 
@@ -154,7 +156,7 @@ func SetAsLabelSelector(ls labels.Set) *LabelSelector {
 	}
 
 	selector := &LabelSelector{
-		MatchLabels: make(map[string]string),
+		MatchLabels: make(map[string]string, len(ls)),
 	}
 	for label, value := range ls {
 		selector.MatchLabels[label] = value

staging/src/k8s.io/apimachinery/pkg/apis/meta/v1/helpers_test.go

@@ -93,6 +93,26 @@ func TestLabelSelectorAsSelector(t *testing.T) {
 	}
 }
 
+func BenchmarkLabelSelectorAsSelector(b *testing.B) {
+	selector := &LabelSelector{
+		MatchLabels: map[string]string{
+			"foo": "foo",
+			"bar": "bar",
+		},
+		MatchExpressions: []LabelSelectorRequirement{{
+			Key:      "baz",
+			Operator: LabelSelectorOpExists,
+		}},
+	}
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		_, err := LabelSelectorAsSelector(selector)
+		if err != nil {
+			b.Fatal(err)
+		}
+	}
+}
+
 func TestLabelSelectorAsMap(t *testing.T) {
 	matchLabels := map[string]string{"foo": "bar"}
 	matchExpressions := func(operator LabelSelectorOperator, values []string) []LabelSelectorRequirement {

staging/src/k8s.io/apimachinery/pkg/labels/selector.go

@@ -367,13 +367,9 @@ func safeSort(in []string) []string {
 
 // Add adds requirements to the selector. It copies the current selector returning a new one
 func (s internalSelector) Add(reqs ...Requirement) Selector {
-	var ret internalSelector
-	for ix := range s {
-		ret = append(ret, s[ix])
-	}
-	for _, r := range reqs {
-		ret = append(ret, r)
-	}
+	ret := make(internalSelector, 0, len(s)+len(reqs))
+	ret = append(ret, s...)
+	ret = append(ret, reqs...)
 	sort.Sort(ByKey(ret))
 	return ret
 }