1. How to update Pmiss efficiently? Most allocations should be fast, so it shouldn't be update with every call to allocate(). What I have now is I update every K calls.
A one-pole low pass filter is a very efficient moving average. https://github.com/D-Programming-Language/druntime/blob/6e55b7aaff7566d374c2f253f831d3489e7fd1a5/src/gc/gc.d#L1732
Feed it with 1 on hit and 0 on miss to get Phit on average.
