title: Twemcache exceeds max memory setting
body: <p>I started twemcache with "twemcache -d -m 20". It should consume no more than 20 MB.
  But according to test, it keeps consuming more memory with "set" then "get". </p>
  
  <pre><code>    import memcache
      mc = memcache.Client(['localhost:11211'])
      i = 0
      while True:
        i+=1
        key = value = str(i)
        mc.set(key, value)
        mc.get(key)
  </code></pre>
  
  <p>I found this because I had a service with -m 4000 and exceeded the cap, and finally killed by os. Anyone know how I can avoid? Thanks in advance.</p>