Determine whether memory location is in CPU cache

Question

It is possible for an operating system to determine whether a page of memory is in DRAM or in swap; for example, simply try to access it and if a page fault occurs, it wasn\'t.<

Answer 1

X86 dont know how to tell if address IS in cache BUT here is how to tell if address WAS in cache

rdtsc
save timestamp
mov eax,address
rdtsc read timestamp counter
calculate timestamp difference
if < threshold then was in cache

threshold has to be determined from documentation or empirically

some machines have cache hit/miss counters which would serve equally well