Puzzling VM behavior in 6.3

[Guy Helmer]

I'm trying to track down a performance regression in a memory-hungry 
application that seems to be related to switching from FreeBSD 6 as of 
2007-01-04 (6.2-ish) to a checkout as of 2007-10-04 (6.3-ish).  With 
these two systems running identical software under load side-by-side on 
identical hardware, we've observed that the disk is busier on the 6.3 
system under the same load, but there shouldn't be much file activity 
other than logging and the swap usage stays at 0.

In trying to track this down, we've found the most significant 
differences are in statistics from parts of the VM system.  A partial 
snapshot of "systat -vm" shows this:

6-STABLE 2007-10-04 sample
Mem:KB    REAL            VIRTUAL                       VN PAGER   SWAP
PAGER
        Tot   Share      Tot    Share    Free           in   out     in
out
Act 2174196   16428  2489520    29168  166416  count
All 2340816   28304  6887896    45636          pages

6-STABLE 2007-01-04 sample
Mem:KB    REAL            VIRTUAL                     VN PAGER  SWAP PAGER
        Tot   Share      Tot    Share    Free         in  out     in  out
Act 2092808   15184  2439012    25424  202272 count
All 3949748   20856157408972    34392         pages

We've also noticed large differences in some sysctl vm stats:
					6-STABLE 2007-01-04	6-STABLE 2007-10-04
vm.stats.vm.v_forkpages: 		660926510		1607169036
vm.stats.vm.v_pdpages: 			608941			1793198

Does this information give anyone a clue as to where I should look next?

Thanks for any help,
Guy

-- 
Guy Helmer, Ph.D.
Chief System Architect
Palisade Systems, Inc.