That's not what I said. My point was that an arena allocator has to be managed at a relatively high level. Similarly, an allocator responsible for 0 on free wou

That's not what I said. My point was that an arena allocator has to be managed at a relatively high level. Similarly, an allocator responsible for 0 on free would be managed at a similar level. They are orthogonal concepts as you say, but there's no reason 0 on free can't be managed by an allocator.