linux-kernel - Re: [RFC v8 PATCH 13/20] memory-hotplug: check page type in get_page

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Message-ID: <50457983.1050304@cn.fujitsu.com>
Date:	Tue, 04 Sep 2012 11:46:11 +0800
From:	Wen Congyang <wency@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	isimatu.yasuaki@...fujitsu.com
CC:	x86@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-acpi@...r.kernel.org,
	linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
	linux-ia64@...r.kernel.org, cmetcalf@...era.com,
	sparclinux@...r.kernel.org, rientjes@...gle.com, liuj97@...il.com,
	len.brown@...el.com, benh@...nel.crashing.org, paulus@...ba.org,
	cl@...ux.com, minchan.kim@...il.com, kosaki.motohiro@...fujitsu.com
Subject: Re: [RFC v8 PATCH 13/20] memory-hotplug: check page type in get_page_bootmem

Hi, isimatu-san

At 09/01/2012 05:30 AM, Andrew Morton Wrote:
> On Tue, 28 Aug 2012 18:00:20 +0800
> wency@...fujitsu.com wrote:
> 
>> From: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
>>
>> There is a possibility that get_page_bootmem() is called to the same page many
>> times. So when get_page_bootmem is called to the same page, the function only
>> increments page->_count.
> 
> I really don't understand this explanation, even after having looked at
> the code.  Can you please have another attempt at the changelog?

What is the problem that you want to fix? The function get_page_bootmem()
may be called to the same page more than once, but I don't find any problem
about current implementation.

Thanks
Wen Congyang

> 
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -95,10 +95,17 @@ static void release_memory_resource(struct resource *res)
>>  static void get_page_bootmem(unsigned long info,  struct page *page,
>>  			     unsigned long type)
>>  {
>> -	page->lru.next = (struct list_head *) type;
>> -	SetPagePrivate(page);
>> -	set_page_private(page, info);
>> -	atomic_inc(&page->_count);
>> +	unsigned long page_type;
>> +
>> +	page_type = (unsigned long) page->lru.next;
>> +	if (page_type < MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE ||
>> +	    page_type > MEMORY_HOTPLUG_MAX_BOOTMEM_TYPE){
>> +		page->lru.next = (struct list_head *) type;
>> +		SetPagePrivate(page);
>> +		set_page_private(page, info);
>> +		atomic_inc(&page->_count);
>> +	} else
>> +		atomic_inc(&page->_count);
>>  }
> 
> And a code comment which explains what is going on would be good.  As
> is always the case ;)
> 
> 

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