title: Linux kernel sendpage function
body: <p>Suppose I have a user space allocated buffer and I want to use sendpage() to send it through NIC.</p>
  
  <p>sendpage supports a zerocopy operation. the following will happen:<br>
  1. get_page - increase reference count<br>
  2. send the page through NIC and receive ACK<br>
  3. put_page  </p>
  
  <p>Is it possible that the pages can be freed or resused before the sendpage actually completes.  </p>
  
  <p>(Considering TCP protocol)  </p>