10.3.10.1 Determining storage usage
To determine storage usage (useful when benchmarking), use the functions
find-object-size. The function room-values is suitable for programmatic use: it returns the values that room prints.
In 32-bit LispWorks,
memory-growth-margin returns the amount by which the Lisp heap can grow, if
set-maximum-memory has been called.
LispWorks User Guide and Reference Manual - 21 Dec 2011