Approaching the limit on PV entries

[John Baldwin]

On Tuesday, March 20, 2012 11:37:57 am Sergey Kandaurov wrote:
> On 22 November 2011 19:29, Mark Saad <nonesuch at longcount.org> wrote:
> > Hello All
> 
> [found this mail in my drafts, not sure if my answer is still useful]
> 
> >  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
> 
> This is how they are calculated.
> 
> pv_entry_max = shpgperproc * maxproc + cnt.v_page_count;
> 
> and, respectively,
> 
> shpgperproc = (pv_entry_max - cnt.v_page_count) / maxproc;
> 
> So, changing one sysctl will change another and vice versa.
> 
> > what pitfalls of changing them are.
> 
> Not known to me (on amd64 platform).
> I have had vm.pmap.shpgperproc=15000 on 8.1 amd64 with 4G RAM
> to make some badly written commercial software to work until it
> was decommissioned to the scrap.

FYI, Alan just removed this warning and the associated sysctls from HEAD 
yesterday because they were made obsolete several years ago.  I think they are 
obsolete even on 7.  Certainly on 8.

-- 
John Baldwin