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Date: Thu, 10 May 2012 14:33:12 -0400
From: Charles Owens <cowens@greatbaysoftware.com>
Organization: Great Bay Software
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Cc: Adam Vande More <amvandemore@gmail.com>, Alan Cox <alan.l.cox@gmail.com>,
	freebsd-stable@freebsd.org
Subject: Re: superpages not solving "PV entries" limit warning
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On 5/10/12 12:37 PM, Alan Cox wrote:
> On Thu, May 10, 2012 at 10:52 AM, Charles Owens 
> <cowens@greatbaysoftware.com <mailto:cowens@greatbaysoftware.com>> wrote:
>
>     That's very helpful!  I had read about that and wondered if it
>     applied to i386.
>
>     Should I have expected "superpages" to completely cure the
>     condition... or does it just help?  Should I now be looking at
>     tuning the related pmap sysctls to give further relief?
>
>
> Superpages won't cure the problem due to the nature of your workload.  
> After a fork, writes to portions of the address space that are both 
> superpages and copy-on-write will trigger demotion, or 
> re-instantiation of the 4KB page granularity PV entries.  Ultimately, 
> repromotion to superpages may occur, but in the meantime, your peak 
> usage of PV entries is only slightly reduced.
>
> The bottom line is that you'll need to resort to tuning.
>
> Alan

Ok.  Very good.


Lastly, since we're talking about this (for the future) -- is enabling 
of superpages generally recommended for amd64?

Thanks,

Charles