linux-kernel - Re: [PATCH 2/2] x86 e820: Introduce memmap=resetusablemap for kdump usage

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Message-ID: <51073207.7040607@zytor.com>
Date:	Mon, 28 Jan 2013 18:20:55 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Thomas Renninger <trenn@...e.de>, x86@...nel.org,
	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
	vgoyal@...hat.com, horms@...ge.net.au
Subject: Re: [PATCH 2/2] x86 e820: Introduce memmap=resetusablemap for kdump
 usage

On 01/28/2013 06:19 PM, Yinghai Lu wrote:
> On Mon, Jan 28, 2013 at 6:11 PM, H. Peter Anvin <hpa@...or.com> wrote:
>> On 01/28/2013 06:10 PM, Yinghai Lu wrote:
>>>
>>>
>>> kexec-tools will change that to E820_KDUMP_RESERVED (or other good name).
>>>
>>> We only need to update kernel to get old max_pfn by
>>> checking E820_KDUMP_RESERVED.
>>>
>>
>> OK, I have asked this before, but I still have not gotten any acceptable
>> answer:
>>
>> Why do we still have max_*_pfn at all?  Shouldn't it all be based on
>> memblocks by now?
>
> saved_max_pfn is used for kdump:
> drivers/char/mem.c::read_oldmem will stop there.
> ...
>          while (count) {
>                  pfn = *ppos / PAGE_SIZE;
>                  if (pfn > saved_max_pfn)
>                          return read;
> ...

That is a non-answer.

Why do we have *any* instances of max_pfn or max_low_pfn in the kernel 
anymore?

	-hpa


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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