Tidbit of information I picked up off a Linux forum after finding unzip had pretty much gobbled all memory after decompressing a large archive.
I ran this command to clear the memory cache (via a simple shell: clearmem).
sh -c "sync; echo 3 > /proc/sys/vm/drop_caches"
Before and after printout...
root@rmp5710:/# free
total used free shared buffers
Mem: 229520 225652 3868 0 1740
-/+ buffers: 223912 5608
Swap: 0 0 0
root@rmp5710:/# clearmem
root@rmp5710:/# free
total used free shared buffers
Mem: 229520 15988 213532 0 476
-/+ buffers: 15512 214008
Swap: 0 0 0
Full story can be found here. You might want to read the comments as most were positive though there were some on the negative side. Works well for me with no ill side affects. I now run it as a nightly cron job and at the end of cgi scripts.. those that run unzip or other memory hogs.
http://www.unixmen.com/how-to-clear-memory-cache-on-linux-servers/