Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> Seems a little hackish, though: we'd be reporting an amount of
> freespace that we've deliberately set to an incorrect value. I'm
> almost thinking we should report the freespace that's actually
> available, on the theory that Bload Is Bad (TM).
IIRC, this code is following the very longstanding precedent of
RelationGetBufferForTuple.
regards, tom lane