linux-kernel - Re: [Patch 8/8] kexec: allow to shrink reserved memory

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Date:	Tue, 18 Aug 2009 14:31:23 +0800
From:	Amerigo Wang <amwang@...hat.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel@...r.kernel.org, tony.luck@...el.com,
	linux-ia64@...r.kernel.org, linux-mm@...ck.org,
	Neil Horman <nhorman@...hat.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 8/8] kexec: allow to shrink reserved memory

KAMEZAWA Hiroyuki wrote:
> On Mon, 17 Aug 2009 17:50:21 +0800
> Amerigo Wang <amwang@...hat.com> wrote:
>
>   
>> Eric W. Biederman wrote:
>>     
>>> Amerigo Wang <amwang@...hat.com> writes:
>>>
>>>   
>>>       
>>>> Not that simple, marking it as "__init" means it uses some "__init" data which
>>>> will be dropped after initialization.
>>>>     
>>>>         
>>> If we start with the assumption that we will be reserving to much and
>>> will free the memory once we know how much we really need I see a very
>>> simple way to go about this. We ensure that the reservation of crash
>>> kernel memory is done through a normal allocation so that we have
>>> struct page entries for every page.  On 32bit x86 that is an extra 1MB
>>> for a 128MB allocation.
>>>
>>> Then when it comes time to release that memory we clear whatever magic
>>> flags we have on the page (like PG_reserve) and call free_page.
>>>   
>>>       
>> Hmm, my MM knowledge is not good enough to judge if this works...
>> I need to check more MM source code.
>>
>> Can any MM people help?
>>
>>     
> Hm, memory-hotplug guy is here.
>   

Hi, thank you!
> Can I have a question ?
>
>   - How crash kernel's memory is preserved at boot ?
>   

Use bootmem, I think.

>     It's hidden from the system before mem_init() ?
>   

Not sure, but probably yes. It is reserved in setup_arch() which is 
before mm_init() which calls mem_init().

Do you have any advice to free that reserved memory after boot? :)

Thanks.



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