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Date: Sun, 28 Jun 2009 19:41:14 -0500
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From: Alan Cox <alan.l.cox@gmail.com>
To: Nathanael Hoyle <nhoyle@hoyletech.com>
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Cc: Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>,
	freebsd-hackers@freebsd.org
Subject: Re: large pages (amd64)
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On Sun, Jun 28, 2009 at 7:14 PM, Nathanael Hoyle <nhoyle@hoyletech.com>wrote:

> Wojciech Puchar wrote:
>
>> i enabled
>> vm.pmap.pg_ps_enabled: 1
>>
>>
>> could you please explain what exactly this values means?
>> because i don't understand why promotions-demotions!=mappings
>>
>> vm.pmap.pde.promotions: 2703
>> vm.pmap.pde.p_failures: 6290
>> vm.pmap.pde.mappings: 610
>> vm.pmap.pde.demotions: 289
>>
>>
>>
>>
>> other question - tried enabling it on my i386 laptop (256 megs ram),
>> always mappings==0, while promitions>demotions>0.
>>
>> certainly there are apps that could be put on big pages, gimp editing 40MB
>> bitmap for example
>>
>
> Just to be clear, since you say i386 (I presume you mean architecture), I
> believe the Physical Address Extensions which allowed 2MB Page Size bit to
> be set was introduced with Pentium Pro. Processors prior to this were
> limited to standard 4KB pages.
>

No.  Many of those processors supported 4MB pages.

Regards,
Alan