VM.sysWrite("LargeObjectAllocator returning ", cell);
  final protected VM_Address allocSlowOnce (boolean isScalar, EXTENT bytes) {    int header = superPageHeaderSize() + cellHeaderSize();    int pages = (bytes + header + PAGE_SIZE - 1)>>LOG_PAGE_SIZE;    VM_Address sp = allocSuperPage(pages);    if (sp.isZero()) return sp;    VM_Address cell = sp.add(header);    Memory.zero(cell, bytes);    VM.sysWrite("LargeObjectAllocator returning ", cell);    return cell;  }