ANSWER:

Is it possible to put anything in a ramdisk? Explicit cache if you will. Not sure if what you’re doing suits this, and you have probably thought aboout it, but i’ll throw it out there

Have a look here:
http://www.linuxinsight.com/proc_sys_vm_hierarchy.html

there are a few bits you can tune easily, just by “cat”ing values in.
vfs_cache_pressure & zone_reclaim_mode jumps out, caveat: only one i have ever tuned is swappiness.

by Tom Newton from http://serverfault.com/questions/381877