std.allocator: FreeList uses simple statistics to control number of items

[Etienne Cimon via Digitalmars-d]

What you could do is calculate the average allocation size and std 
deviantions in a moving window, and the z-score for each freelist and 
use this lookup table:

https://www.stat.tamu.edu/~lzhou/stat302/standardnormaltable.pdf

If P < 0.10 (maybe use this as a setting) this means the probability of 
the next allocations going through this freelist is too low and you can 
decide to tighten the freelist and let the deallocations fall through to 
the underlying allocator.