kernel: Approaching the limit on PV entries...

[Paul A. Procacci]

Bob Johnson wrote:
> 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
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>   
For what it's worth, I just came across a machine with the same exact 
problem, except when I do finally run out of entries, I get a kernel panic.

FBSD 7-RELEASE-p4

~Paul