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

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Message-ID: <4A8927DD.6060209@redhat.com>
Date:	Mon, 17 Aug 2009 17:50:21 +0800
From:	Amerigo Wang <amwang@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	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

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?

Thanks.

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