linux-kernel - Re: [PATCH] x86_64: setup saved_max

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Date:	Fri, 3 Nov 2006 03:05:08 +0900
From:	"Magnus Damm" <magnus.damm@...il.com>
To:	"Mel Gorman" <mel@....ul.ie>
Cc:	"Magnus Damm" <magnus@...inux.co.jp>, linux-kernel@...r.kernel.org,
	"Vivek Goyal" <vgoyal@...ibm.com>, "Andi Kleen" <ak@....de>,
	fastboot@...ts.osdl.org
Subject: Re: [PATCH] x86_64: setup saved_max_pfn correctly (kdump)

Hi Mel,

Thanks for your input! Great work with the add_active_range() code.

On 11/3/06, Mel Gorman <mel@....ul.ie> wrote:
> Hey Magnus,
>
> I see what you are doing and why. However if you look in
> arch/x86_64/kernel/setup.c, you'll see
>
>          parse_early_param();
>
>          finish_e820_parsing();
>
>          e820_register_active_regions(0, 0, -1UL);
>
> If you just called e820_register_active_regions(0, 0, -1UL) before
> parse_early_param(), would it still fix the problem without having to call
> e820_register_active_regions(0, 0, -1UL) twice?

Well, I guess it is possible to move the
e820_register_active_regions() up, but I'm not sure if that would give
us anything.

We need to call e820_register_active_regions() before e820_end_of_ram,
that's for sure, but the "exactmap" code in parse_memmap_opt() sets
e820.nr_map to 0 after the call to e820_end_of_ram(). Then it adds a
new set of user-supplied ranges to the e820 map which then need to be
registered using e820_register_active_regions().

So yeah, we can move the function up above parse_early_param() but
then we need to insert another call to e820_register_active_regions()
somewhere after all user-supplied ranges have been added.

Another solution could be to rewrite e820_end_of_ram() to instead scan
e820.map[] backwards from e820.nr_map - 1 to locate the last ram page.
But can you do that in two lines of code? =)

Thanks!

/ magnus
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