title: kvm balloon driver results in different total-memory then requested
body: <p>I have ubuntu and installed on it several qemu-kvm guests, running also ubuntu.</p>
  
  <p>I'm using libvirt to change the guests' memory allocation. But always encounter a constant difference between the requested memory allocation and the actual memory allocation I query from the <code>Total</code> field in the <code>top</code> command inside the guests.</p>
  
  <p>The difference is the same in all the guests, and consistent. 
  In one machine I installed it is 134MB (allocated is less then requested), In another one it is 348MB.</p>
  
  <p>I can live with it, I just don't know the reason. Does someone encounter this kind of problem? Maybe solved it?</p>
  
  <p>Thanks</p>