It's possible, absolutely, but if you allocate N such fragments one after another, do some allocations in them, and then finalize them from first to the last, t

It's possible, absolutely, but if you allocate N such fragments one after another, do some allocations in them, and then finalize them from first to the last, there will be gaps left less than 16 GiB in size, so they could only be reused for small allocations; and IIRC allocators with special support for huge allocations (e.g. using so-called huge pages) do not reuse that memory for "normal-sized" allocations (although I can be wrong on this). So it's a tradeoff: this fragmentation is not that bad but it's still noticeable in a sufficiently long-running program because 16 GiB is 2**34 so you only can make 16 Ki such allocations before you hit the 2**48 limit. And if you could just simply remap them!..