rm_init(9) on FreeBSD
The text 9d1b2013c68d, as FreeBSD 16.0-CURRENT (2026-10-27), FreeBSD 15.1-RELEASE, FreeBSD 15.0-RELEASE, FreeBSD 14.5-RELEASE, FreeBSD 14.4-RELEASE, FreeBSD 14.3-RELEASE, FreeBSD 14.2-RELEASE, FreeBSD 14.1-RELEASE, FreeBSD 14.0-RELEASE shipped it. The page shows this text now.
kernel reader/writer lock optimized for read-mostly access patterns