title: Is it a safe to use Direct-IO write and Page Cache read at the same time?
body: <p>For instance, open a file twice, direct-io writes with one fd, and page cache reads with the other?</p>
  
  <p>How to define <code>safe</code>: Write some data from direct-io fd and then expect to read them <code>immediately</code> from page-cache fd</p>