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

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Date:	Sun, 13 Jul 2008 11:17:45 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Andi Kleen" <andi@...stfloor.org>
Cc:	"Arjan van de Ven" <arjan@...radead.org>,
	"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

On Sun, Jul 13, 2008 at 7:57 AM, Andi Kleen <andi@...stfloor.org> wrote:
> 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.

with this patch, my 256g system still use gbpages for 1g-3g, 4g-256g

YH
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