large pages (amd64)

[Nathanael Hoyle]

Alan Cox wrote:
> On Sun, Jun 28, 2009 at 7:14 PM, Nathanael Hoyle <nhoyle at 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
> _______________________________________________
>   
Having been corrected by both you and Joerg (thank you!), I went back to 
re-verify my understanding. It appears that while I was slightly mixing 
PAE in with PSE, PSE support for 4MB pages was introduced 'silently' 
with the Pentium, and documented first with the Pentium Pro.  I haven't 
found anything that points to earlier inclusion. Certainly the 80386 
processor specifically, I am fairly confident would be limited to the 
4KB pages.

Agreed? Or are you aware of earlier usage than the Pentium for 4MB pages?

Thanks,
-Nathanael