How to measure the usage of disk cache?

Load Average itself is not very informative about the reasons of overload, so I want an additional characteristic: the percent of disk read operations that are done from cache. To measure it, I probably need: - the amount of data read from cache (or, instead, the amount of data read directly from disk); - the total amount of read data. Both for the certain period of time, f.e., 1 second. Is this information available in procfs/sysfs?