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

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Message-Id: <20090819171346.aadfeb2c.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Wed, 19 Aug 2009 17:13:46 +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 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 ?


Thanks,
-Kame




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