title: Sum of RSS memory in ps less than memory actually used
body: <p>We have two machines with identical configuration and use (we have two balanced Siebel application servers in them).</p>
  
  <p>Normally, we have a very similar RAM usage in them (around 7 Gb).
  Recently, we've have a sudden increase of RAM in only one of them and now we have close to 14 Gb utilization of RAM in that machine.</p>
  
  <p>So, for very similar boxes, we have one of them using 7Gb of RAM while the other one is consuming 14 Gb.</p>
  
  <p>Now, using <em>ps aux</em> command to determine which process it's using all this additional memory, we see memory consumption is very similar in both machines. Somehow, we don't see any process that's using those 7 Gb of additional RAM.</p>
  
  <p>Let's see:
  <code>
  Machine 1:
               total       used       free     shared    buffers     cached
  Mem:         15943      15739        204          0        221       1267
  -/+ buffers/cache:      14249       1693
  Swap:         8191          0       8191
  </code></p>
  
  <p>So, we have 14249 Mb usage of RAM.</p>
  
  <p><code>
  Machine 2:
               total       used       free     shared    buffers     cached
  Mem:         15943      15636        306          0        962       6409
  -/+ buffers/cache:       8264       7678
  Swap:         8191          0       8191
  </code></p>
  
  <p>So, we have 8264 Mb usage of RAM.</p>
  
  <p>I guess, the sum of Resident Set Size memory of ps should be equal or bigger to this value. According to <a href="https://stackoverflow.com/questions/7880784/what-is-rss-and-vsz-in-linux-memory-management">this answer</a> is how much memory is allocated to the process and is in RAM (including memory from shared libraries). We don't have any memory in SWAP.</p>
  
  <p>However:</p>
  
  <p>Machine 1:</p>
  
  <p><code>
  ps aux | awk 'BEGIN {sum=0} {sum +=$6} END {print sum/1024}'
  8357.08
  </code></p>
  
  <p>8357.08 &lt; 14249 -> NOK!</p>
  
  <p>Machine 2:</p>
  
  <p><code>
  ps aux | awk 'BEGIN {sum=0} {sum +=$6} END {print sum/1024}'
  8468.63
  </code></p>
  
  <p>8468.63 > 8264 -> OK</p>
  
  <p>What do I get wrong? How can I find where this "missing" memory is?</p>
  
  <p>Thank you in advance</p>