purge(8) flushes and clears the disk buffers, which is not the issue that kills me with my old macbook with 4G ram.
It looks like disk cache expiration is slow and tends to kick in when it's a bit too late. With the speed that modern apps chew through memory, I'm sent into a swap thrash and get sluggish response and beachballs.
MemoryKeeper on the App store seems to mostly clear the file cache and do some -fu to compact memory (maybe it's a memory defragment, the docs are a little lacking in technical details.) When I manually run it, everything runs great until the free memory dries up and I'm back in that alloc/swapthrash/cachepurge cycle again.
I wrote a tiny C program for linux to force cache expirations (in a very sloppy but reasonably portable way) back in '98 that I've started using again on osX, it fixes the issue and runs quite a bit quicker than MemoryKeeper. I can make it available if anyone else wants it.
