The function returns the previous settings of
minimum-overflow. (see set-gc-parameters for details of these.)
If you use
avoid-gc, use normal-gc later to reset the parameters to their default settings.
avoid-gc 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 to increase the default size of segments in the lower generations (typically generations 0 and 1. This will lead to less frequent garbage collections.
LispWorks User Guide and Reference Manual - 20 Sep 2017