Eh, nothing stops you from using a single buffer, but with different offsets for each open call. So I don't really see the problem unless you have so much buffer space allocated that it becomes problematic.
A "single buffer, but with different offsets for each open call" is identical to "allocate one buffer per socket" (you "allocated" the per-socket buffer by subdividing a larger allocation). And even if you don't "have so much buffer space allocated that it becomes problematic", it's still a waste of memory.
