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.
result is t on success and nil on failure.
This function is useful when it is known that a generation will need to grow. After enlarge-generation is called, the garbage collector is saved the work of deducing that the generation must grow.
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 - 20 Sep 2017