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

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Message-ID: <20061102182011.GE8074@in.ibm.com>
Date:	Thu, 2 Nov 2006 13:20:11 -0500
From:	Vivek Goyal <vgoyal@...ibm.com>
To:	Magnus Damm <magnus.damm@...il.com>
Cc:	Mel Gorman <mel@....ul.ie>, Magnus Damm <magnus@...inux.co.jp>,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@....de>,
	fastboot@...ts.osdl.org
Subject: Re: [PATCH] x86_64: setup saved_max_pfn correctly (kdump)

On Fri, Nov 03, 2006 at 03:05:08AM +0900, Magnus Damm wrote:
> 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? =)
> 

Is there are reason that why e820_end_of_ram() should be looking at active
regions instead of dicrectly probing e820 memory map? If no, then modifying
e820_end_of_ram() wil save us extra calls.

Thanks
Vivek
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