Locking a file backed mdconfig into memory

[Matthew D Fleming]

On Fri, Jun 04, 2010 at 08:20:49AM -0400, John Baldwin wrote:
> Hmmm, I would just try increasing NKPT then.  You might have to poke 
> around in sys/amd64 to see what the default size is and how to tune 
> it.

When Isilon did the stable/7 merge and amd64 default NKPT changed from 
240 to 32 amd64 started having weird pmap issues during boot.  At panic 
time the stack wasn't very useful, and I didn't finish debugging the 
issue since eventually I just had to get something working.  We just 
reverted NKPT to 240 and it worked for us.  I didn't see an anything in 
optsions.amd64 so I hard-coded it in amd64/include/pmap.h.

Supposedly amd64 can deal with a small NKPT and grow dynamically, but it 
didn't seem to work for us. :-( Perhaps when we do the next merge 
project I'll have a few days to devote to debugging the root cause.

Thanks,
matthew