code: func (dc *DeploymentController) scaleDownOldReplicaSetsForRecreate(oldRSs []*apps.ReplicaSet, deployment *apps.Deployment) (bool, error) {
  	scaled := false
  	for i := range oldRSs {
  		rs := oldRSs[i]
  		// Scaling not required.
  		if *(rs.Spec.Replicas) == 0 {
  			continue
  		}
  		scaledRS, updatedRS, err := dc.scaleReplicaSetAndRecordEvent(rs, 0, deployment)
  		if err != nil {
  			return false, err
  		}
  		if scaledRS {
  			oldRSs[i] = updatedRS
  			scaled = true
  		}
  	}
  	return scaled, nil
  }
docs: // scaleDownOldReplicaSetsForRecreate scales down old replica sets when deployment strategy is "Recreate".