So, then, even if there is an overflow of pages with free space, stepping
up the vacuum schedule may help this eventually catch up.
As for an automated way to set this up, if the FSM size cannot be adjusted
without a restart of the postmaster, then on startup, you could take a
number of pages currently with free space or a percentage of the number of
pages, which ever is greater. The percentage could have a default, and
also be configurable.