title: How to understand iOS memory physical footprint
body: <p>According to this WWDC iOS Memory Deep Dive talk <a href="https://developer.apple.com/videos/play/wwdc2018/416" rel="nofollow noreferrer">https://developer.apple.com/videos/play/wwdc2018/416</a>, memory footprint equals to dirty and swapped size combined. However, when I use <code>vmmap -summary [mempgraph]</code> to inspect my memgraphs, many times they don't add up. In this particular case <a href="https://i.stack.imgur.com/71W9q.png" rel="nofollow noreferrer">vmmap</a>
  , memory footprint = 118.5M while the dirty size is 123.3M. How can footprint be smaller than the dirty size?</p>
  <p>In the same WWDC talk, it's mentioned that <code>heap --sortBySize [memgraph]</code> can be used to inspect heap allocations, and I see from my memgraph that the heap size is about 5M <code>All zones: 110206 nodes (55357344 bytes) </code>, which is much smaller than the <code>MALLOC</code> regions in the vmmap result. Doesn't malloc allocate spaces in the heap?</p>