4.9 boot problem on em0 platform.

[Don Bowman]

> From: Deepak Jain [mailto:deepak at ai.net]
> As a part of tracking down a performance issue, I tried building a 
> custom kernel (with just IPFW, DUMMYNET added, NMBCLUSTERS, 
> commenting 
> out MATH_EMULATE, INET6, I386, I486). The system is currently 
> running a 
> kernel from a similar machine with the same settings.  The 
> machine does 
> run on this kernel:  4.9-RELEASE FreeBSD 4.9-RELEASE #8, with 
> the above 
> options, but I have not been able to compile a 4.9-RELEASE #2 
> (which is 
> the source tree on the machine) kernel that has an identical 
> config file.
> 
> So, when it builds itself from -RELEASE sources, it hangs at:
> 
> "pmap_mapdev: Couldn't alloc kernel virtual memory" I couldn't find a 
> reference to anything recent. Nothing non-default (from a GENERIC 
> kernel) with respect to ACPI has been touched. I see a reference to 
> -CURRENT from 9/03, but that's it.

Just a guess, but i think you've bumped nmbclusters or nmbufs up
too much (or perhaps maxsockets, maxfds, ...) and have run out of
KVA.

You can tune clusters & mbufs in loader.conf without recompiling
kernel. You will want to see what vm.zone_kmem_pages, vm.zone_kmem_kvaspace
are showing you, vmstat -z, vmstat -m, etc.

You may want to alter VM_KMEM_SIZE_SCALE to e.g. '2' if you are
trying to put more into the kernel mem space.