Apple's MCL used the MMU for the stock Motorola 68020+ (M68020 + MMU, 68030/40 with included MMU, ...) processors for an efficient GC: the Ephemeral GC, using a table of changed memory pages, which was maintained by the MMU.

This idea was added by Apple to their first ARM CPUs, to get an efficient GC on tiny devices, running either a Lisp dialect or in the product, the Virtual Machine for NewtonScript.

See for some info on the ARM610 and Garbage Collection: https://wiki.preterhuman.net/A_Call_to_ARM

But today's CPUs are very very different: an example is Apples M2 Ultra SOC. We don't have a Lisp implementation which has an even remote idea how to get "full" performance out of the combination of a larger number of Efficient+Performance cores, many GPU cores, Neural processing Unit + media engine + high-bandwidth unified memory. Most current more advanced Lisp engines make only use of a (not so large) count of multiple CPUs (only a few use multiple cores for the GC), some SIMD features, none (AFAIK) make use of the rest...