An integer between 0 and 7, inclusive.
count-gen-num-allocation returns the amount of allocated data in generation gen-num. If include-lower-generations is non-nil, the returned value allocation also includes the data in the younger generations.
count-gen-num-allocation is implemented only in 64-bit LispWorks. It is not relevant to the Memory Management API in 32-bit implementations, where you can use room-values instead.
LispWorks User Guide and Reference Manual - 20 Sep 2017