Weird memory issue

<pre>Hi, I have a very weird memory issue (as you may have guessed from the title :) ). There's a discrepency between the memory accumulated by the various applications (using "ps -eF" to collect that) and the memory reported by system monitor/"free". Basically, I have around 0.5GB of memory that is not occupied by any application, but is not free as well. (It is not used as cache as well) I restarted X (logged out and in again), but it didn't help. free's output: total used free shared buffers cached Mem: 4056964 2874328 1182636 0 481360 592220 -/+ buffers/cache: 1800748 2256216 Swap: 6723160 31412 6691748 and on the other hand: $ ps -eF | grep -v COMMAND | awk '{rsum+=$6}END{print rsum}' 1309016 I'm running Ubuntu 9.10 64bit. I had some zombie processes, but I killed their parent process and that made them go away (and freed up some memory, but not all that's missing) Any ideas how to further debug this would be appreciated. Thanks! </pre>