void update_sets() {

  {- -------------------------------------------
  (1) G1CollectedHeap::update_sets_after_freeing_regions() を呼び出すだけ.
      ---------------------------------------- -}

        // We'll recalculate total used bytes and recreate the free list
        // at the end of the GC, so no point in updating those values here.
        _g1h->update_sets_after_freeing_regions(0, /* pre_used */
                                                NULL, /* free_list */
                                                &_humongous_proxy_set,
                                                false /* par */);
      }