refactor getPodsToDelete comment

pkg/controllers/collaset/synccontrol/scale.go

@@ -58,11 +58,11 @@ func getPodsToDelete(filteredPods []*collasetutils.PodWrapper, replaceMapping ma
 		}
 
 		if replacePairPod, exist := replaceMapping[pod.Name]; exist && replacePairPod != nil {
-			// don't scaleIn new pod until origin pod is deleted, if you want to delete new pod, please delete it by label
+			// don't selective scaleIn newPod (and its originPod) until replace finished
 			if replacePairPod.ToDelete {
 				continue
 			}
-			// new pod not service available, just scaleIn it
+			// when scaleIn origin Pod, newPod should be deleted if not service available
 			if _, serviceAvailable := replacePairPod.Labels[appsv1alpha1.PodServiceAvailableLabel]; !serviceAvailable {
 				needDeletePods = append(needDeletePods, replacePairPod)
 			}