After Acme was written, I replaced most of the buffer management code in Sam with that from Acme, which was more efficient - it did the database stuff in a different order that was one pass quicker. It's possible the old code used an arena allocator, I don't remember, but it's possible you're referring to the code in samterm, which grew up on the Blit and likely had some compacting arena management code in it to keep the memory footprint small. As always, though, my memory may be faulty; it compacts too often.
-rob