linux-kernel - Re: [Patch 0/8] V5 Implement crashkernel=auto

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Date:	Mon, 31 Aug 2009 11:27:07 +0800
From:	Amerigo Wang <amwang@...hat.com>
To:	michael@...erman.id.au
CC:	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>,
	"M. Mohan Kumar" <mohan@...ibm.com>, 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 0/8] V5 Implement crashkernel=auto

Michael Ellerman wrote:
> On Wed, 2009-08-26 at 23:15 -0400, Amerigo Wang wrote:
>   
>> V4 -> V5:
>>  - Rename the global functions, as suggested by Andrew.
>>  - Save some macros, as suggested by Andrew.
>>  - Change the high threshold, from 32G to 4G.
>>  - Change the low threshold on ppc, suggested by ppc developers.
>>  - Make the mm part as a seperate function, suggest by Eric.
>>  - Make the IA64 code more readable.
>>  - Reorder the patchset again, since review from mm people is done.
>>
>> V3 -> V4:
>>  - Reorder the patches.
>>  - Really free the reserved memory, instead of remapping it.
>>    (Thanks to KAMEZAWA Hiroyuki!)
>>  - Release the reserved memory resource when the size is 0.
>>  - Use strict_strtoul() instead of simple_strtoul().
>>
>> V2 -> V3:
>>  - Use more clever way to calculate reserved memory size, especially for IA64.
>>  - Add that patch that implements shrinking reserved memory
>>
>> V1 -> V2:
>>  - Use include/asm-generic/kexec.h, suggested by Neil.
>>  - Rename a local variable, suggested by Fenghua.
>>  - Fix some style problems found by checkpatch.pl.
>>  - Unify the Kconfig docs.
>>
>> This series of patch implements automatically reserved memory for crashkernel,
>> by introducing a new boot option "crashkernel=auto". This idea is from Neil.
>>
>> In case of breaking user-space applications, it modifies this boot option after
>> it decides how much memory should be reserved.
>>
>> On different arch, the threshold and reserved memory size is different. Please
>> refer patch 7/8 which contains an update for the documentation.
>>
>> Patch 8/8 implements shrinking reserved memory at run-time, which is useful
>> when more than enough memory is reserved automatically.
>>
>> This patchset _is_ already tested on x86_64, IA64 and ppc64.
>>     
>
> I don't want to sound like a micro-kernel zealot, I'm not, but I'm still
> unconvinced as to why the auto logic needs to go in the kernel. What is
> the compelling reason that the kernel needs to do this calculation vs
> some userspace tool? We already have the syntax that allows defining a
> different crash size depending on the size of RAM.
>   

Take a look at the x86 part, it can not be done _directly_ in kernel 
command line with the syntax.

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