PSOldGen::PSOldGen(size_t initial_size,
                   size_t min_size, size_t max_size,
                   const char* perf_data_name, int level):

  {- -------------------------------------------
  (1) フィールドの初期化
      ---------------------------------------- -}

      _name(select_name()), _init_gen_size(initial_size), _min_gen_size(min_size),
      _max_gen_size(max_size)
    {}