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

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Message-ID: <4A8A6B8F.7000604@redhat.com>
Date:	Tue, 18 Aug 2009 16:51:27 +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 Tue, 18 Aug 2009 14:31:23 +0800
> Amerigo Wang <amwang@...hat.com> wrote:
>   
>> Hi, thank you!
>>     
>>> Can I have a question ?
>>>
>>>   - How crash kernel's memory is preserved at boot ?
>>>   
>>>       
>> Use bootmem, I think.
>>
>>     
> I see.
>
> In x86,
>  
>   setup_arch()
> 	-> reserve_crashkernel()
> 		-> find_and_reserve_crashkernel()
> 			-> reserve_bootmem_generic()
>
> Then, all "active range" is already registered and there are memmap.
>
>
>   
>>>     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++
>
> But it has no argumetns. Maybe you need your own function or modification.
> online_pages() does very similar. But, hmm,.. writing something open coded one
> for crashkernel is not very bad, I think.
>   

Nice help!

Yeah, I think we can make that be a generic wrapper function so that 
both free_initmem() and shrink_crash_memory() can use it.

Then I will update and resend the whole patchset.

Thank you!



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