Increasing KVM on amd64

[Artem Belevich]

Alan,

Thanks a lot for the patch. I've applied it to RELENG_7 and it seems
to work great - "make -j8 buildworld" succeeds, linux emulation seems
to work well enough to run linux-sun-jdk14 binaries, ZFS ARC size is
bigger, too. So far I didn't see any ZFS-related KVM shortages either.

The only problem is that everything is fine as long as vm.kmem_size is
set to less or equal to 4096M. As soon as I set it to 4100M or
anything larger, kernel crashes on startup. I'm unable to capture
exact crash messages as they keep scrolling really fast on the screen
for a few seconds until the box reboots. Unfortunately  the box does
not have built-in serial ports, so the messages are gone before I can
see them. :-(

Is there a way to bump up KVM size even further - beyond 6GB? I've got
a box with 8GB or RAM and would like let ZFS ARC use most of it which
would require pretty large vm.kmem_max to fit it in.

Thanks,
--Artem