FS cache hit rate.. How do I find it?

[Naoki <naoki valuecommerce com>]

Howdy,

I'm looking for a method of determining the cache hit rate for block IO
(or indeed any hit rate numbers would be nice).

Anybody know how I can pull this data from the system?

note: There was an oracle patch (loadable kernel module) going around
that does what I want but it's specific to oracle data files.