title: Java heap size not entirely used
body: <p>I'm currently monitoring my running java application with Visual VM: <a href="http://visualvm.java.net/" rel="nofollow noreferrer">http://visualvm.java.net/</a></p>
  
  <p>I'm stressing the memory usage by with -Xmx128m.</p>
  
  <p>When running I see the heap size increasing to 128m (as expected) however the used heap converges to approximately 105m before I run into a java heap space error.</p>
  
  <p><img src="https://i.stack.imgur.com/5jZ1e.png" alt="enter image description here"></p>
  
  <p>Why are these remaining 20m, not used?</p>