linux-kernel - Re: [Patch 6/8] powerpc: add CONFIG_KEXEC_AUTO

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Message-ID: <20090825102422.GA14591@in.ibm.com>
Date:	Tue, 25 Aug 2009 15:54:22 +0530
From:	"M. Mohan Kumar" <mohan@...ibm.com>
To:	Amerigo Wang <amwang@...hat.com>
Cc:	Michael Ellerman <michael@...erman.id.au>,
	linux-kernel@...r.kernel.org, tony.luck@...el.com,
	linux-ia64@...r.kernel.org, Neil Horman <nhorman@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	kamezawa.hiroyu@...fujitsu.com, Andi Kleen <andi@...stfloor.org>,
	akpm@...ux-foundation.org, bernhard.walle@....de,
	Fenghua Yu <fenghua.yu@...el.com>, Ingo Molnar <mingo@...e.hu>,
	Anton Vorontsov <avorontsov@...mvista.com>
Subject: Re: [Patch 6/8] powerpc: add CONFIG_KEXEC_AUTO_RESERVE

On Tue, Aug 25, 2009 at 02:37:12PM +0800, Amerigo Wang wrote:
> M. Mohan Kumar wrote:
>> On Mon, Aug 24, 2009 at 11:44:03PM +1000, Michael Ellerman wrote:
>>   
>>> On Fri, 2009-08-21 at 02:55 -0400, Amerigo Wang wrote:
>>>     
     
>>> That aside, I don't see how this will be useful in practice, if it only
>>> works for memory sizes over 4G? Or are we saying that people with less
>>> than 4G don't need crash kernels? If we're not saying that, those users,
>>> or those users' distros, still need to do some logic to work out if they
>>> have < 4GB of memory and if so pick a crash kernel size. So why can't
>>> they pick the size in the > 4GB case also?
>>>     
>>
>> True, I wanted to test the patch and when tested on a ppc64 machine which
>> has RAM less than 4GB, I have to modify arch_default_crash_size routine to
>> return 256MB (I didn't have a PPC64 machine with more than 4GB RAM handy).
>> So its better to consider machines with less than 4GB RAM also.
>>   
>
> OK, how about 2G on ppc? Is it safe to reserve 256M when I have 2G?

I would prefer 2G-4G 128MB.

>
>> PPC64 crashkernel base is always 32MB. So at least ppc64 code should have
>> its own arch_default_crash_base to return 32MB to avoid the kernel warning
>> message "Crash kernel location must be 0x2000000"
>>   
> Hmm, good point, how about KDUMP_KERNELBASE? It looks fine for both ppc  
> and ppc64.

Yes, you can use KDUMP_KERNELBASE for arch_default_crash_base

Regards,
M. Mohan Kumar
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