root@cs0:~# mdconfig -a -t swap -s 2g
md0
root@cs0:~# gpart create -s gpt md0
md0 created
root@cs0:~# gpart add -t freebsd-swap -s 1g md0
md0p1 added
root@cs0:~# gpart add -t freebsd-swap -l LABELtest md0
md0p2 added
root@cs0:~# gpart show md0
=> 34 4194237 md0 GPT (2.0G)
34 2097152 1 freebsd-swap (1.0G)
2097186 2097085 2 freebsd-swap (1.0G)
root@cs0:~# gpart show -l md0
=> 34 4194237 md0 GPT (2.0G)
34 2097152 1 1 (1.0G)
2097186 2097085 2 LABELtest (1.0G)
root@cs0:~#
PR: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=204737