A generation number.
The amount (in bytes) by which the generation is to be enlarged.
The function enlarge-generation enlarges generation gen-num by size bytes. If possible, an existing segment in generation gen-num is enlarged, otherwise a new segment of size size is added to the generation.
enlarge-generation is most useful in non-interactive applications, where relatively long GC delays are not a problem. In this case, enlarging generations 0 and 1 by several Mb may improve the overall performance of the GC.