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

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Date:	Fri, 21 Aug 2009 11:03:09 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Amerigo Wang <xiyou.wangcong@...il.com>
Cc:	Amerigo Wang <amwang@...hat.com>,
	"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 Fri, 21 Aug 2009 09:59:27 +0800
Amerigo Wang <xiyou.wangcong@...il.com> wrote:

> On Fri, Aug 21, 2009 at 09:34:52AM +0900, KAMEZAWA Hiroyuki wrote:
> >On Thu, 20 Aug 2009 17:15:56 +0800
> >Amerigo Wang <amwang@...hat.com> wrote:
> >    
> >> > 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?
> >> 
> >Hmm ? Could you show me the code you use ?
> 
> (Sorry that I reply to you with my gmail, my work email can't send out
> this message, probably because one of the destinations is broken...
> I am the same person, don't be confused. :-)
> 
> Sure. Below is it:
> 
> +    for (addr = end + 1; addr < crashk_res.end; addr += PAGE_SIZE) {
> +        printk(KERN_DEBUG "PFN is valid? %d\n", pfn_valid(addr>>PAGE_SHIFT));
> +        ClearPageReserved(virt_to_page(addr));
> +        init_page_count(virt_to_page(addr));
> +        free_page(addr);
> +        totalram_pages++;
> +    }
> 
> 
> pfn_valid() returns 1, and oops happens at ClearPageReserved().
> ('addr' is right between crashk_res.start and crashk_res.end)

Confused, 
  if    pfn_valid(addr >> PAGE_SHIFT) == true 

you should do
	ClearPageReserved(pfn_to_page(addr >> PAGE_SHIFT));

because addr is physical address, not virtual.
I guess crashk_res.end is physical address....

Thanks,
-Kame


> 
> Thank you!
> 

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