title: What does docker mean when it says "Memory limited without swap"
body: <p>I'm getting a warning when I run docker:</p>
  
  <blockquote>
    <p>WARNING: Your kernel does not support swap limit capabilities or the cgroup is not mounted. Memory limited without swap.</p>
  </blockquote>
  
  <p>I'm trying to work out what this means, particularly the phrase "Memory limited without swap."</p>
  
  <p>Does this mean that the container can use more memory than you would normally allow it by using the swap space of the host machine? Or does it mean that the container can't use the swap space, even when the host runs out of memory completely? Is it caused by having no swap space configured? Is it irrelevant if you aren't using swap anyway?</p>
  
  <p>Note: I'm not interested in how to fix it - there are lots of results about that on google. I'm interested in what it <em>means</em>, and why it matters.</p>