TRUNCATE pg_largeobject

Is it safe?

This table is around 500GB and because of performance reasons
I slowly moved all large objects to regular files on a NetApp
share.

Now it shows 0 records:

# select count(*) from pg_largeobject;
count
-------
0
(1 row)

but disk space and RAM by the free space map is still occupied.
I'd like to clean it up.
A VACUUM FULL would probably do it, but it would take several
hours with heavy I/O and I'd like to avoid that on a production
server.

Can I safely issue a "TRUNCATE pg_largeobject"?
It is v8.1.9.

Thanks!