i386 PAE kernel works fine on 10-stable

[Ian Lepore]

This is an out of the blue FYI post to let people know that despite all
the misinformation you'll run across if you search for information on
FreeBSD PAE support, it (still) works just fine.  I've been using it
(for reasons related to our build system and products at $work) since
2006, and I can say unequivocally that it works fine on 6.x, 8.x, and
now 10.x (and presumably on the odd-numbered releases too but I've never
tried those).

In my most recent testing with 10-stable, I found it was compatible with
drm2 and radeonkms drivers and I was able to run Xorg and gnome just
fine.  All my devices, and apps, and even the linuxulator worked just
fine.

One thing that changed somewhere between 8.4 and 10.1 is that I had to
add a kernel tuning option to my kernel config:

  option  KVA_PAGES=768	    # Default is 512

I suspect that the most frequent use of PAE is on laptops that have 4gb
and the default tuning is adequate for that.  My desktop machine has
12gb and I needed to bump up that value to avoid errors related to being
unable to create new kernel stacks.

-- Ian