linux-kernel - RE: [RFC Patch 2/2] kexec: allow to shrink reserved memory

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Date:	Tue, 11 Aug 2009 13:55:16 -0700
From:	"Yu, Fenghua" <fenghua.yu@...el.com>
To:	'Neil Horman' <nhorman@...hat.com>,
	'Amerigo Wang' <amwang@...hat.com>
CC:	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
	"'linux-ia64@...r.kernel.org'" <linux-ia64@...r.kernel.org>,
	"'Eric W. Biederman'" <ebiederm@...ssion.com>,
	'Andi Kleen' <andi@...stfloor.org>,
	"'akpm@...ux-foundation.org'" <akpm@...ux-foundation.org>,
	'Ingo Molnar' <mingo@...e.hu>
Subject: RE: [RFC Patch 2/2] kexec: allow to shrink reserved memory

>On Tue, Aug 11, 2009 at 06:39:32AM -0400, Amerigo Wang wrote:
>>
>> This patch implements shrinking the reserved memory for crash kernel,
>> if it is more than enough.
>>
>> For example, if you have already reserved 128M, now you just want 100M,
>> you can do:
>>
>> # echo $((100*1024*1024)) > /sys/kernel/kexec_crash_size
>>
>> Signed-off-by: WANG Cong <amwang@...hat.com>
>> Cc: Neil Horman <nhorman@...hat.com>
>> Cc: Eric W. Biederman <ebiederm@...ssion.com>
>> Cc: Andi Kleen <andi@...stfloor.org>
>>
>
>Since the reserved area is also used for heap in the new kernel, isn't this
>mechanism going to guarantee a non-bootable kernel.  It seems like it
>shrinks
>the reserved area to the size of the image, leaving no additional memory
>for
>heap allocations during the kernels boot.  Or am I missing something?

I think this mechanism need user to have the intelligence to decide the size of memory reserved for crashed kernel. The crash kernel size should include all space a crashed kernel need. This mechanism just does whatever crashed kernel size the user specifies.

Thanks.

-Fenghua
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