code: public static void unmap(final FileChannel fileChannel, final long address, final long length)
      {
          try
          {
              MappingMethods.UNMAP_ADDRESS.invoke(fileChannel, address, length);
          }
          catch (final IllegalAccessException | InvocationTargetException ex)
          {
              LangUtil.rethrowUnchecked(ex);
          }
      }
docs: Unmap a region of a file.
  
  @param fileChannel which has been mapped.
  @param address     at which the mapping begins.
  @param length      of the mapped region.