Hello,

For the past few days, I've been pouring over source in the NetBSD tree
trying to figure out stuff about proper values for NKMEMPAGES (I sent an
email about the default values to tech-kern and port-m68k).

I've had softdep problems on m68k, but almost none on i386 (but not none).
I never imagined a connection between NKMEMPAGES and softdeps, but I came
across some emails from tech-smp from the end of August, 2000, that
discussed increasing NKMEMPAGES to account for really heavy softdep usage.

m68k and VAX machines have really modest values for the defaults of
NKMEMPAGES; could someone who knows a lot about the internals of the VM
system elabourate on whether this could have anything to do with softdeps
being problematic on m68k and VAX?

It does seem a little weird that NKMEMPAGES is static or in a really small
range on these systems no matter how much memory is available. NKMEMPAGES
is supposed to be physical ram / 4 / page size, or 64 NKMEMPAGES per
megabyte for 4k pages.

Here is a clip from my email to tech-kern:

(Number of NKMEMPAGES, and page size)
Amiga:          384 (8k)
Atari:          384 (8k)
hp300:          1536 to 2048 (4k)
luna68k         768 (4k)
mac68k:         768 (4k)
mvme68k:        1024 to 1536 (4k)
news68k:        1024 (4k)
next68k:        1024 (4k)
sun3:           384 (8k)
x68k:           768 to 1024 (4k)

Compare this to PowerPC, Alpha, and i386 (up to 32768); are they really
THAT different?

With memory as cheap as it is, I have most of my m68k machines maxed out -
I have several Quadras with 136 megs, three Amigas with 144 megs, one
Amiga with 256. I even have 104 megs in my VAX (1024 pages, 4k sized
pages)

If this doesn't get changed in the sources, then could someone at least
tell me what a good guideline might be?


The original post:

I've looked into the default values for NKMEMPAGES for all of the
architectures NetBSD supports, and I'm a little puzzled. According to the
comments in the code, the number of NKMEMPAGES is calculated by physical
ram size times some machine dependent code.

Looking at i386 machines, this is true: a machine with 192 megs of memory
has 12260 vm.nkmempages; a machine with 256 megs has 16280.

But Amigas have 384 always, whether 16 or 256 megs.

John Klos