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

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Message-ID: <20090821024736.GB4447@cr0.nay.redhat.com>
Date:	Fri, 21 Aug 2009 10:47:36 +0800
From:	Amerigo Wang <xiyou.wangcong@...il.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Amerigo Wang <xiyou.wangcong@...il.com>,
	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, Aug 21, 2009 at 11:03:09AM +0900, KAMEZAWA Hiroyuki wrote:
>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....

Excellent! You are right!

In fact, when I read the kexec code at the first time, I thought
'crashk_res' should hold physical address too, but after reading
more code I dropped that idea, so I am wrong. :-/

I will resend the whole patchset soon. It works now!

Thanks for your nice help, Hiroyuki!

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