Hi, This affects amd64, alpha and aarch64, but only 1 and 2 CPU systems so far. Any more and it's still off by default. Only the default has changed so the sysctl (vm.ubc_direct) still works for turning it on and off manually.
This works great for me on amd64 but needs some tweaks to handle many CPUs. I have some ideas on that one and hopefully will have something to try soon. Cheers, Andrew