how to set vfs.zfs.arc.max in 15-current ?

[void]

Is there a new way to set arc.max in 15-current?

It's no longer settable (except to "0") in main-n265801 (Oct 7th)
while multiuser.

# sysctl vfs.zfs.arc.max=8589934592
vfs.zfs.arc.max: 0
sysctl: vfs.zfs.arc.max=8589934592: Invalid argument

--