Matthew D Fleming wrote:
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.
NKPT controls the number of page table pages that are initially
allocated at the bottom of the top 2GB of the kernel address space.
However, the vast majority of the kernel address space, 510GB in FreeBSD
>=7.3, is below these page table pages. The page table pages for this
region are dynamically allocated as needed.
If you're booting a kernel and modules greater than 64GB in size, then I
can certainly see why you would need to increase NKPT.
John, is there some way to know at boot time how big the kernel and
modules were? Then, we could probably eliminate NKPT.
Alan
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