A generation number.
The amount (in bytes) by which the generation is to be enlarged.
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.
enlarge-generation is implemented only in 32-bit LispWorks. It is not relevant to the Memory Management API in 64-bit implementations. In 64-bit implementations you can use set-default-segment-size.
LispWorks User Guide and Reference Manual - 13 Feb 2015