title: Increase of virtual memory without increse of VmSize
body: <p>I searched for my problem in Google and at this site but i still don't understand the solution.</p>
  
  <p>I have piece of <code>MPI</code> program which <code>RECV</code> some data. Program crashes on big arrays with error of insufficient virtual memory, and so i started to consider <code>/proc/self/status</code> file.</p>
  
  <p>Before <code>MPI_RECV</code> it was:</p>
  
  <pre><code>Name:   model.exe                                                               
  VmPeak:   841640 kB
  VmSize:   841640 kB
  VmHWM:     15100 kB
  VmRSS:     15100 kB
  VmData:   760692 kB
  </code></pre>
  
  <p>And after:</p>
  
  <pre><code>Name:   model.exe                                                            
  VmPeak:   841640 kB
  VmSize:   841640 kB
  VmHWM:    719980 kB
  VmRSS:    719980 kB
  VmData:   760692 kB
  </code></pre>
  
  <p>I test it on Ubuntu and through System Monitor i saw this memory increasing. But i was confused that there are no changes in <code>VmSize</code>(and <code>VmPeak</code>) parameters.</p>
  
  <p>And the question is - what is the indicator of real memory usage? </p>
  
  <p>Does it mean, that true indicator is <code>VmRSS</code>? (and <code>VmSize</code> is only allocated but still not used memory)</p>