vm.pmap.shpgperproc syslog messages

[D Hill]

On Wed, 4 Jun 2008 at 18:46 -0500, tinguely at casselton.net confabulated:

>>  I just noticed today I'm starting to get messages in ../messages stating:
>>
>>     Approaching the limit on PV entries, consider increasing either the
>>     vm.pmap.shpgperproc or the vm.pmap.pv_entry_max sysctl.
>>
>>  I did some searching and don't really know what is going on. I did a
>>  search using sysctl for all pmap knobs and this is what they are
>>  currently:
>>
>>     vm.pmap.pmap_collect_active: 0
>>     vm.pmap.pmap_collect_inactive: 0
>>     vm.pmap.pv_entry_spare: 51310
>>     vm.pmap.pv_entry_allocs: 67575721858
>>     vm.pmap.pv_entry_frees: 67574088800
>>     vm.pmap.pc_chunk_tryfail: 0
>>     vm.pmap.pc_chunk_frees: 416252902
>>     vm.pmap.pc_chunk_allocs: 416262928
>>     vm.pmap.pc_chunk_count: 10026
>>     vm.pmap.pv_entry_count: 1633059
>>     vm.pmap.shpgperproc: 500
>>     vm.pmap.pv_entry_max: 6125408
>>
>>  I did increased vm.pmap.shpgperproc to 500 from 200 and immediately saw
>>  vm.pmap.pv_entry_max increase as well.
>>
>>  This server is a Dell PowerEdge 6850 with four 3.0Gz dual core Zeon
>>  processors and 12Gb ram. The server's only purpose is a spam filter. It is
>>  running SpamAssassin, ClamAV, Postfix and MySQL. The server is pretty
>>  memory intensive. Active memory usually doesn't drop below 8Gb.
>>  SpamAssassin usually has roughly 24 children running all the time
>>  consuming ~120Mb per child. MySQL is currently taking ~5.5Gb.
>>
>>  Can someone shed light on what is going on or what needs to be tweaked?
>
> pv_entry are entries that are used to keep track of which processes are
> sharing a physical page.
>
> pv_entry are allocated in groups (chunks to fill a page) - 168 for the AMD64.
>
> The more RAM and processes that you have, the more probably that the pages
> are shared in multiple processes and more pv_entrys are needed.
>
> It looks like you are well below the pv_entry_max with shpgperproc at 500.

I figured out what was going on when the messages hit the ../messages log. 
I have a cronjob that executes a MySQL script to optimize tables. It was 
during that time when the syslog messages were logged. Since increasing 
vm.pmap.shpgperproc yesterday, I haven't seen anything in the logs.

Thanks for the response.