İf you profiled yor file app. and every thing is okey. That means you need extra real memory. This is normal behavior. Blowtorch is very rigth.

but you can try vmtune may be. Just very veak oportunity. Look at vmtune man page. I can't remember the parameters now. But you can get faster LRU (Last recently used ) chain.

what happens;
your app needs for memory looks at real memory and can't find and uses swapp . So you must release some memory pages more faster.