unmounting all file systems is too slow

[asomers]

During a reboot, ZFS must unmount all file systems. This is frequently very slow. The problem seems to be that zfs_umount calls zfs_teardown which calls txg_wait_synced. And syncing a transaction is very slow if a scrub or resilver is ongoing. In such cases, I've frequently seen the reboot take tens of minutes, and sometimes hours (assuming I don't hit the power button first). What can we do to speed things up? Manually pausing scrubs before rebooting seems to help, but I can't manually pause a resilver. And I shouldn't have to do it manually. Can we add some kind of pre-shutdown hook that suspends all scrubs and resilvers? Or somehow batch multiple unmounts together and only wait on a single TXG sync?

FreeBSD 14, amd64, if it matters.