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

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Date:	Tue, 18 Aug 2009 17:25:52 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Amerigo Wang <amwang@...hat.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

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.

Thanks,
-Kame







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