memorySwapUsed(platform = process.platform) {
    switch (platform) {
      case 'darwin':
        return memorySwapUsedDarwin();

      case 'freebsd':
      case 'openbsd':
        return memorySwapUsedBsd();

      case 'linux':
        return memorySwapUsedLinux();

      case 'win32':
        return memorySwapUsedWindows();
    }

    logger.warn(`Swap status is unsupported on the '${platform}' platform.`);

    return null;
  }
Determines the amount of swap/virtual memory currently in use.

@private
@method memorySwapUsed
@param {String=process.platform} platform The current hardware platform.
                                          USED FOR TESTING ONLY.
@return {null|Number} The amount of used swap space, in bytes.  `null` if
                       the used swap space cannot be determined.