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

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Message-ID: <Pine.LNX.4.64.0611022240350.27544@skynet.skynet.ie>
Date:	Thu, 2 Nov 2006 22:41:32 +0000 (GMT)
From:	Mel Gorman <mel@....ul.ie>
To:	Magnus Damm <magnus.damm@...il.com>
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)

On Fri, 3 Nov 2006, Magnus Damm wrote:

> Hi Mel,
>
> Thanks for your input! Great work with the add_active_range() code.
>

Thanks

> 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.
>

Ah right, I see the problem now and why you need to do things that way in 
your patch. Sorry about that.

> 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? =)
>

Nope. As the path you are doing this in is not time-critical, the patch is 
fine to me.

> Thanks!
>
> / magnus
>

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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