void PSMarkSweep::allocate_stacks() {

  {- -------------------------------------------
  (1) (この関数では, PreservedMark 用の領域の確保を行う.
       See: PreservedMark)
      ---------------------------------------- -}

  {- -------------------------------------------
  (1) (変数宣言など)
      ---------------------------------------- -}

      ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
      assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");

      PSYoungGen* young_gen = heap->young_gen();

      MutableSpace* to_space = young_gen->to_space();

  {- -------------------------------------------
  (1) _preserved_marks フィールド(及び関連する _preserved_count フィールドと _preserved_count_max フィールド)の値を設定する.
      (ここでは, To 領域内の未使用の領域(top から end まで)を PreservedMark 用の領域としている)
      ---------------------------------------- -}

      _preserved_marks = (PreservedMark*)to_space->top();
      _preserved_count = 0;

      // We want to calculate the size in bytes first.
      _preserved_count_max  = pointer_delta(to_space->end(), to_space->top(), sizeof(jbyte));
      // Now divide by the size of a PreservedMark
      _preserved_count_max /= sizeof(PreservedMark);
    }