Comment by stevekemp

You're probably right, in practice it would be just fine.

That said if you look at a lot of the basic GC approaches you end up either moving all the allocated and live objects, or running through a mark & sweep dance which gives you holes in your allocation region - and causes problems with fragmentation.

Choosing the right kind of GC, knowing your constraints, could probably sidestep these problems, but there seems to be nothing obvious with the simple two-headed bump-allocator decribed in the post, so long as the lifecycles don't change over time - ruining the simplicity of the arena-based approach.