title: max_old_space_size set to 4gb, actually limits to 2GB
body: <p>I'm writing a NodeJS 6.3.1 application under Gentoo Linux 64 bit.
  In this machine I generally have 9GB out of 16GB free memory and 49GB swap space barely used.</p>
  
  <p>I use the following code to the test the memory limit of my node.js application:</p>
  
  <pre><code>var arr = []; 
  var c=0;
  while(arr.push('foo')) {if (++c%100000 == 0) {console.info(process.memoryUsage());}}
  </code></pre>
  
  <p>Running this script with no extra parameters to node, the last memoryUsage line is this:</p>
  
  <pre><code>{ rss: 1032232960, heapTotal: 1015185408, heapUsed: 1008680024 }
  </code></pre>
  
  <p>Now running node.js with <code>--max_old_space_size=4096</code>, the last memoryUsage line is this:</p>
  
  <pre><code>{ rss: 2202341376, heapTotal: 2189082624, heapUsed: 2177311480 }
  </code></pre>
  
  <p>now with 8000 limit:</p>
  
  <pre><code>{ rss: 1934946304, heapTotal: 1921712128, heapUsed: 1909919344 }
  </code></pre>
  
  <p>What am I missing? How can I increase the heap to 4 or 8GB?</p>