How to exclude directory with mandb?

I mounted a relatively slow 9p drive at /mnt/p which is relatively slow (2-4 MiB/s). I run mandb and find that it will access /mnt/p and freeze there:

Processing manual pages under /mnt/p/wr/msys2/mingw64/share/man...
Updating index cache for path `/mnt/p/wr/msys2/mingw64/share/man/man1'. Wait...mandb: warning: /mnt/p/wr/msys2/mingw64/share/man/man1/fsf-funding.7.gz: ignoring bogus filename
mandb: warning: /mnt/p/wr/msys2/mingw64/share/man/man1/gfdl.7.gz: ignoring bogus filename
mandb: warning: /mnt/p/wr/msys2/mingw64/share/man/man1/gpl.7.gz: ignoring bogus filename
Updating index cache for path `/mnt/p/wr/msys2/mingw64/share/man/man3'. Wait...^C

I want to exclude /mnt directory for mandb but I can’t find any information about how to achieve this in mandb’s manpage and google.