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

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Date:	Thu, 20 Aug 2009 17:15:56 +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 Wed, 19 Aug 2009 10:41:13 +0800
> Amerigo Wang <amwang@...hat.com> wrote:
>
>   
>> KAMEZAWA Hiroyuki wrote:
>>     
>>> On Tue, 18 Aug 2009 18:35:32 +0800
>>> Amerigo Wang <amwang@...hat.com> wrote:
>>>
>>>   
>>>       
>>>> KAMEZAWA Hiroyuki wrote:
>>>>     
>>>>         
>>>>> On Tue, 18 Aug 2009 14:31:23 +0800
>>>>> Amerigo Wang <amwang@...hat.com> wrote:
>>>>>   
>>>>>       
>>>>>           
>>>>>>>     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? :)
>>>>>>
>>>>>>     
>>>>>>         
>>>>>>             
>>>>> Let's see arch/x86/mm/init.c::free_initmem()
>>>>>
>>>>> Maybe it's all you want.
>>>>>
>>>>> 	- ClearPageReserved()
>>>>> 	- init_page_count()
>>>>> 	- free_page()
>>>>> 	- totalram_pages++
>>>>>   
>>>>>       
>>>>>           
>>>> Just FYI: calling ClearPageReserved() caused an oops: "Unable to handle 
>>>> paging request".
>>>>
>>>> I am trying to figure out why...
>>>>
>>>>     
>>>>         
>>> Hmm...then....memmap is not there.
>>> pfn_valid() check will help you. What arch ? x86-64 ?
>>>   
>>>       
>> Hmm, yes, x86_64, but this code is arch-independent, I mean it should 
>> work or not work on all arch, no?
>>
>> So I am afraid we need to use other API to free it...
>>
>>     
> The, problem is whether memmap is there or not. That's all.
> plz see init sequence and check there are memmap.
> If memory-for-crash is obtained via bootmem,
> Don't you try to free memory hole ?
>   

Hi,

It looks like that mem_map has 'struct page' for the reserved memory, I 
checked my "early_node_map[] active PFN ranges" output, the reserved 
memory area for crash kernel is right in one range. Am I missing 
something here?

I don't know why that oops comes out, maybe because of no PTE for thoese 
pages?

Thanks.


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