title: TCP socket buffer sizes should also be an even multiple of the MSS for the connection
body: <p>There is a paragraph in "unix network programming", says:  </p>
  
  <blockquote>
    <p>To avoid wasting potential buffer space, the TCP socket buffer sizes
    should also be an even multiple of the MSS for the connection. Some
    implementations handle this detail for the application, rounding up
    the socket buffer size after the connection is established (p. 902 of
    TCPv2). This is another reason to set these two socket options before
    establishing a connection. For example, using the default 4.4BSD size
    of 8,192 and assuming an Ethernet with an MSS of 1,460, both socket
    buffers are rounded up to 8,760 (6 x 1,460) when the connection is
    established. This is not a crucial requirement; the additional space
    in the socket buffer above the multiple of the MSS is simply unused.</p>
  </blockquote>
  
  <p>I can not imagine how "<strong>wasting</strong> potential buffer space" happens. Why <strong>waste</strong>?<br>
  What will happen if the buffer size is not an even multiple of the MSS?<br>
  Can anybody help me and explain it? Or can anybody offer an example or scenario?  </p>