10.3.10.4 Controlling the garbage collector
The functions that are most likely to be useful for controlling the GC are room, check-fragmentation, gc-generation (replacing
mark-and-sweep) and try-move-in-generation.
Other potentially useful functions and macros are
gc-if-needed, enlarge-generation, normal-gc,
with-heavy-allocation and try-compact-in-generation.
LispWorks User Guide and Reference Manual - 22 Dec 2009