I tried to increase the size of the buffer cache, using the following
kernel config options:

options NBUF=512
options BUFPAGES=512

So instead of getting 204 pages using 835584 bytes, I should get
512 pages using 2097152 bytes.  However, from what I can tell, this
does not work properly.  I've traced the "problem" to this line of
code in machdep.c:


        if (bufpages == 0)
                if (physmem < btoc(2 * 1024 * 1024))
                        bufpages = physmem / 10 / CLSIZE;
                else
                        bufpages = (btoc(2 * 1024 * 1024) + physmem) / 20 / CLS>

        bufpages = min(NKMEMCLUSTERS * 2 / 5, bufpages);
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

What is this NKMEMCLUSTERS constant?  Where does it get set?  Why does
it override the BUFPAGES option?

here is the brief description in the options man page:

     options NKMEMCLUSTERS=value
     number of slots in the kernel submap "kmem_map".  [Better description,
     please? Chris CGD had some comments that I didn't understand.] Default is
     <look this up>.  Increase this value if you get "out of space in
     kmem_map" panics.


So, what's going on here?

Sean

---
Sean Sweda
sweda@ibl.org                     http://www.ibl.org/~sweda 
sweda@netcommandos.com            http://advantage.netcommandos.com