> You allocate a memory arena when the HTTP request comes. From that point on, every "allocation" is equivalent to bumping a pointer in that arena. If the arena gets full, we allocate another and chain it to the previous one, as a linked list.

Didn't you just describe the regular memory management as applied by OS in a process scope? At the completion of the process, all memory allocated by the process is reclaimed.

On some systems this approach is combined with granular quotas to allow multi-process coexistence.

Shifting this sort of memory management over to application scope may yield benefits now, but ultimately it's an OS-level concern.