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

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Message-ID: <CAE9FiQVG4ShGKSdjzYhQaXNNhS=MVNJg=QqG1yW-mAUscErXMA@mail.gmail.com>
Date:	Mon, 28 Jan 2013 18:19:07 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
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 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;
...
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