[DOCS] No, that's backwards.

The documentation at
https://www.postgresql.org/docs/current/static/storage-vm.html says that
the visibility map "keeps track of which pages contain only unfrozen
tuples".

This is wrong; it keeps track of all-frozen pages not all-unfrozen.

Trivial patch attached.
--
Vik Fearing                                          +33 6 46 75 15 36
http://2ndQuadrant.fr     PostgreSQL : Expertise, Formation et Support