title: Page Cache for shared memory
body: <p>In the following link within the 4th image from the top:</p>
  
  <p><a href="http://duartes.org/gustavo/blog/post/page-cache-the-affair-between-memory-and-files" rel="nofollow">http://duartes.org/gustavo/blog/post/page-cache-the-affair-between-memory-and-files</a></p>
  
  <ul>
  <li>The scenario depicted, is that of two processes, "render" and "3drender", sharing a file. The author is going about describing how the sharing mechanism, plays along with the page cache.</li>
  <li>Originally render had it's virtual pages mapped onto the page cache.</li>
  <li>In step 4 "render" is allocated a new anonymous page of it's own, which would contain certain changes, that it would want to make to "scene.dat #2".</li>
  <li>Once "render" makes it's changes, how is this change reflected to "3drender" which has continued to point to the page cache page frame containing "scene.dat #2" ?</li>
  <li>Also, shouldn't this change made by "render", make it's way back to the page cache, there by replacing the old page cache copy of "scene.dat #2" ?</li>
  <li>The part that remains unclear to me, is what happens "after" one of the processes writes to a shared page and how this "update" makes it's way to the page cache and disk, such that other processes which share the same file, see this change.</li>
  </ul>
  
  <p>It be great if someone could throw some light.</p>
  
  <p>Thanks,
  VIjay</p>