title: Limit buffer cache used for mmap
body: <p>I have a data structure that I'd like to rework to page out on-demand.  <code>mmap</code> seems like an easy way to run some initial experiments.  However, I want to limit the amount of buffer cache that the <code>mmap</code> uses.  The machine has enough memory to page the entire data structure into cache, but for test reasons (and some production reasons too) I don't want to allow it to do that.</p>
  
  <p>Is there a way to limit the amount of buffer cache used by <code>mmap</code>?</p>
  
  <p>Alternatively, an <code>mmap</code> alternative that can achieve something similar and still limit memory usage would work too.</p>