The function reduce-memory frees memory and tries to reduce the size of the Lisp image, without enlarging it even temporarily. It is implemented only in 32-bit LispWorks.
reduce-memory has the same effect as clean-down, except that clean-down may temporarily increase the size of the image in order to be able to promote from lower generations. reduce-memory never increases the image size, which means that it may fail to promote. This will cause future garbage collections to be slower, until the promotion actually occurs.
reduce-memory is intended to be used when the operating system signals that the memory is low. Using clean-down in this situation may cause a temporary increase in size, which may cause the system to run out of memory, or maybe just kill the Lisp process. In other circumstances clean-down should do a better job (and you might also consider try-move-in-generation).
If full is nil, reduce-memory frees memory and promotes live objects to generation 2. When full is non-nil, reduce-memory frees and promotes to generation 3. The default value of full is nil.
reduce-memory returns the new size of the Lisp image after reduction, in bytes.
nil, which is different from clean-down where it defaults to t.reduce-memory with no argument or nil differs from (clean-down nil) by trying to reduce the memory. (clean-down nil) frees and promotes, but does not try to reduce the size (and may actually increase it).reduce-memory is implemented only in 32-bit LispWorks.LispWorks User Guide and Reference Manual - 13 Feb 2015