increasing PMAP_SHPGPERPROC (was: FreeBSD 5.4 or 6.0 as postgresql-server)

[Claus Guttesen]

> > I'd be interested in your experiences w/6.0.  Would you mind testing
> > the onboard bge nics at the kind of loads that was causing them to
> > puke under 5.4?  I've got same system and as of yet not encountered
> > issues w/ the onboard bge nics.  The machine is also at the latest
> > BIOS, however, so that may contribute as well.

I just put our new db-server in production and so far everything works
fine, including the two build-in bge-nics. When load hit the server
the following showed up in /var/log/messages:

kernel: collecting pv entries -- suggest increasing PMAP_SHPGPERPROC

The default value is found in /usr/src/sys/amd64/conf/NOTES and says:

# The value below is the one more than the default.
#
options         PMAP_SHPGPERPROC=201

But I can't find any rule of thumb on what value to raise it to, 402,
512, just above it says:

# Set the number of PV entries per process.  Increasing this can
# stop panics related to heavy use of shared memory.  However, that can
# (combined with large amounts of physical memory) cause panics at
# boot time due the kernel running out of VM space.

regards
Claus