linux-kernel - Re: pud_bad vs pud

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Message-ID: <20090205215050.GB28097@elte.hu>
Date:	Thu, 5 Feb 2009 22:50:50 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Hugh Dickins <hugh@...itas.com>,
	William Lee Irwin III <wli@...ementarian.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: pud_bad vs pud_bad


* Jeremy Fitzhardinge <jeremy@...p.org> wrote:

>> I sincerely hope 0!  I shed no tears at losing support for NUMAQ, but why 
>> should we be forced to double all the 32-bit ptes?  You want us all to be 
>> using NX?  Or you just want to cut your test/edit matrix - that I can 
>> well understand!
>
> Yes, that's the gist of it.  We could simplify things by having only one 
> pte format and only have to parameterise with 3/4 level pagetables.  We'd 
> lose support for non-PAE cpus, including the first Pentium M (which is 
> probably still in fairly wide use, unfortunately).

We'd also lose a fair bit of performance (not to mention the pagetable 
footprint doubling that Hugh already mentioned) on 32-bit PAE capable 
systems that dont actually have RAM above 4G physical.

Bad idea really ...

	Ingo
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