kernel: Approaching the limit on PV entries...

[Bob Johnson]

A web server with several jailed copies of Apache is having problems
that seem to be caused by incorrect IPFW rules, but in the process of
working on that, I find in the log the following repeated many times:

Oct  8 23:29:50 spider kernel: Approaching the limit on PV entries,
consider increasing either the vm.pmap.shpgperproc or the
vm.pmap.pv_entry_max sysctl.
Oct  8 23:30:52 spider kernel: Approaching the limit on PV entries,
consider increasing either the vm.pmap.shpgperproc or the
vm.pmap.pv_entry_max sysctl.

sysctl gives me:

# sysctl vm.pmap
vm.pmap.pmap_collect_active: 0
vm.pmap.pmap_collect_inactive: 0
vm.pmap.pv_entry_spare: 45818
vm.pmap.pv_entry_allocs: 595716945
vm.pmap.pv_entry_frees: 595133939
vm.pmap.pc_chunk_tryfail: 0
vm.pmap.pc_chunk_frees: 3543052
vm.pmap.pc_chunk_allocs: 3546795
vm.pmap.pc_chunk_count: 3743
vm.pmap.pv_entry_count: 583006
vm.pmap.shpgperproc: 200
vm.pmap.pv_entry_max: 2243305

The system:
FreeBSD .... 7.0-RELEASE-p5 FreeBSD 7.0-RELEASE-p5 #0: Wed Oct  1
07:51:58 UTC 2008
root at amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC  amd64

Can someone briefly explain what this is telling me and how to decide
which sysctl to increase? I have found some old postings that predate
the sysctls that suggested increasing shpgperproc in the kernel
configuration, about 50 at a time until the problem goes away, but I
still have no clue what that is accomplishing.

Also, the system has been rebooted since I collected those messages,
and they aren't happening any more, but I expect they will reappear
eventually. Until then I probably can't actually test anything.

Thanks for your time,

-- Bob Johnson
   fbsdlists at gmail.com