Go has this problem too but they choose to use a "conservative collector" which will just assume that if something is a word that contains something that happens to be a valid location in memory it considers that location to be alive even if it's actually garbage.

The main drawback is that if you're not sure if something is really a pointer, you cannot relocate objects and compact the heap. Ocaml has a generational collector with a nursery implemented with a semi space collector. A semi space collector performs a collection which involves moving live objects and leaving the garbage behind. This is very efficient because young objects are less likely to survive and thus the amount of work is proportional to the amount of surviving objects and not the garbage.