Comment by blasdel

fork() in Ruby would be much better if MRI's garbage collector wasn't so awful -- because it marks every reachable object in each collection cycle, it's impossible for MRI processes to take advantage of the kernel's copy-on-write memory sharing post-fork. You can't even just let the processes gobble up space and let the kernel's VM sort it out -- anything that gets swapped out will have to be paged back in to be marked by the GC. Churn.