else if (!LAZY_SWEEP) makeFreeListFromMarkBits(block, sizeClass);
  private final void sweepBlocks() {    for (int sizeClass = 0; sizeClass < SIZE_CLASSES; sizeClass++) {      VM_Address block = firstBlock.get(sizeClass);      while (!block.isZero()) {        /* first check to see if block is completely free and if possible         * free the entire block */        VM_Address next = BlockAllocator.getNextBlock(block);        if (isEmpty(block, sizeClass))          freeBlock(block, sizeClass);        block = next;      }    }  }