I'm completely aware of everything you said, but it's not what I asked. I was very specifically not asking what is theoretically possible but what actually happ

I'm completely aware of everything you said, but it's not what I asked. I was very specifically not asking what is theoretically possible but what actually happens in practice. Because I don't see any evidence that this is actually the case in practice. For a memory allocator that has a legitimate general-purpose deallocator (i.e. ones that are reasonable replacements for malloc/free), my experience says this kind of overhead being worth optimizing is very much hypothetical rather than the reality. Of course for allocators that skip half the steps (e.g. don't bother to return memory dynamically or only work in specific cases) then the story might be very different but it's not really fair to compare them against general purpose ones? Now I'm perfectly happy to accept my imagination/experience is just lacking and that's why I don't see such use cases, but I'm seeing multiple other top comments voicing the same concerns as I am, so I'm mostly suggesting a plausible example to demonstrate this is likely to really help convince people this might be the right thing to focus on.