linux-kernel - Re: [PATCh] x86: overmapped fix when 4K pages on tail

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Message-ID: <874p6t25n5.fsf@basil.nowhere.org>
Date:	Sun, 13 Jul 2008 16:57:50 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Yinghai Lu <yhlu.kernel@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCh] x86: overmapped fix when 4K pages on tail - 64bit

Arjan van de Ven <arjan@...radead.org> writes:

> On Wed, 9 Jul 2008 20:15:02 -0700
> Yinghai Lu <yhlu.kernel@...il.com> wrote:
>
>> 
>> 
>> fix phys_pmd_init to make sure not to return big value than end.
>> 
>> also print out range split:1G/2M/4K
>> 
>> Signed-off-by: Yinghai Lu <yhlu.kernel@...il.com>
>
>
> Making an accurate mapping solves a lot of potentially nasty/tricky
> corner cases, so I like the approach

It also means that e.g. on a 1GB system the direct mapping will 
never use 1GB pages.

And the CPU has to handle this anyways because all the old 
kernels overmap and no x86 CPU can drop support for all old
kernels.

In the end it means only large systems will benefit from 1GB
pages, which seems wrong to me.

-Andi
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