private int getNumMissingInstances(
      List<SingularityTaskId> matchingTaskIds,
      SingularityRequest request,
      SingularityPendingRequest pendingRequest) {
    if (request.isOneOff() && pendingRequest.getPendingType() == PendingType.ONEOFF) {
      return 1;
    }

    final int numInstances = request.getInstancesSafe();

    return numInstances - matchingTaskIds.size();
  }