int bytes = cursor.diff(start).toInt();
VM_Extent bytes = cursor.diff(start).toWord().toExtent();
  public void release() {    // Unmapping is useful for being a "good citizen" and for debugging    int bytes = cursor.diff(start).toInt();    int pages = Conversions.bytesToPages(bytes);    if (ZERO_ON_RELEASE)         Memory.zero(start, VM_Extent.fromInt(bytes));    if (Options.protectOnRelease)      LazyMmapper.protect(start, pages);    releaseHelp(start, pages);    cursor = start;    //-if RVM_WITH_GCSPY    if (VM_Interface.GCSPY)      Plan.releaseVMResource(start, bytes);    //-endif  }