Approaching the limit on PV entries

[Mark Saad]

Hello All
 I want to get to the bottom of a warning in dmesg. On 7.2-RELEASE and
7.3-RELEASE I have seen the following warning in dmesg.

Approaching the limit on PV entries, consider increasing either the
vm.pmap.shpgperproc or the vm.pmap.pv_entry_max sysctl.

So looking around I see a few posts here and there about how to tune
the sysctls to address the warning however I am not 100% sure what
each value does.
It appears changing vm.pmap.shpgperproc affects the value of
vm.pmap.pv_entry_max . Can someone explain the relationship of the two
sysctls. Also
what pitfalls of changing them are. Also why would setting
kern.ipc.shm_use_phys=1  effect the pv entries. Is this supposed to
lower the pv entries ?

Some details on the systems where I saw this.

FreeBSD 7.3-RELEASE-p5 amd64
2G RAM + 2G SWAP
1 single core opteron
Superpages are enabled
The servers are high traffic web-servers serving static content.

tunings

kern.ipc.maxsockbuf=2097152
kern.ipc.nmbclusters=32768
kern.ipc.somaxconn=1024
kern.maxfiles=131072
kern.maxfilesperproc=32768
net.inet.tcp.inflight.enable=0
net.inet.tcp.path_mtu_discovery=0
net.inet.tcp.recvbuf_max=2097152
net.inet.tcp.sendbuf_max=2097152
net.isr.direct=1
vm.pmap.shpgperproc=600
vfs.read_max=64



http://lists.freebsd.org/pipermail/freebsd-hackers/2009-December/030193.html
http://lists.freebsd.org/pipermail/freebsd-hackers/2009-July/029076.html
http://forums.freebsd.org/showthread.php?t=17786

-- 
mark saad | nonesuch at longcount.org