Comment 351 for bug 620074

Interesting thing is cache usage and inability to drop most of it. From my understanding memory cache can be dropped if it's not dirty (has been "wittenback" to disk) this brought me to this thread about lack of writeback:
http://marc.info/?l=linux-kernel&m=113919849421679&w=2

On the other side /proc/meminfo shows only ~160kB of dirty memory. Cache shows 880868 KB. echo 3 > /proc/sys/drop_caches doesn't do anything. So why cache can't be freed? Is it possible to have cache leak?