I might be missing something but why do we need to recheck whether each pages is all-frozen after insertion? I wonder if we can set all-frozen without checking all tuples again in this case.
It's possible that the user may have inserted unfrozen rows (via regular INSERT or COPY without FREEZE option) before inserting frozen rows. So we can't set the all-visible/all-frozen flag unconditionally. I also find it safer to do an explicit check to ensure we never accidentally mark a page as all-frozen. Since the check is performed immediately after the page becomes full and only once per page, there shouldn't be any additional IO cost and the check should be quite fast.
