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List:       freebsd-hackers
Subject:    Re: Approaching the limit on PV entries
From:       Mark Saad <nonesuch () longcount ! org>
Date:       2012-03-22 17:48:29
Message-ID: CAMXt9NbY9Opz6r2JpLrOGEZ3nU3amc5-5xLcKA0CyFq19mMZBg () mail ! gmail ! com
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On Thu, Mar 22, 2012 at 8:03 AM, John Baldwin <jhb@freebsd.org> wrote:
> On Wednesday, March 21, 2012 4:20:17 pm Mark Saad wrote:
>> On Wed, Mar 21, 2012 at 12:39 PM, Sergey Kandaurov <pluknet@gmail.com> wrote:
>> > On 21 March 2012 19:19, John Baldwin <jhb@freebsd.org> wrote:
>> >> On Tuesday, March 20, 2012 11:37:57 am Sergey Kandaurov wrote:
>> >>> On 22 November 2011 19:29, Mark Saad <nonesuch@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.
>> >
>> > Yep, and since switching to direct map (somewhere around 7.x on amd64?)
>> > made PV entry limit factually obsolete, this is really cool.
>> >
>> > --
>> > wbr,
>> > pluknet
>>
>> Interesting so this warning is relevant in 7.x ?
>
> No, looks like it was obsolete starting with 7.0.
>
> --
> John Baldwin

Any chance it could be mfc'ed to 7-STABLE ?

-- 
mark saad | nonesuch@longcount.org
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