title: memory leak, size of objects tracked by gc is far less than memory usage of process
body: <p>Our object is a big system.
  As we know there must be some memory leak in it by now. But it is so difficult to find the reason. Everytime memory used by the process reaches gigabytes, the response of it is so slow.
  cpu usage viewed from "top" is alwasy 100%, even the process has no job to do.</p>
  
  <p>We have used objgraph and meliae to debug this problem, nothing to suspect. But we found one weird problem, the total size of objects got by gc.get_objects() is not equal with the memory usage viewed from "top", for example it is 50M, but 150M from "top". </p>
  
  <p>Could anyone give us a direction? Thanks.</p>