linux-kernel - Re: [PATCH 5/10] memory-hotplug : memory-hotplug: check page type in get_page

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Date:	Fri, 19 Oct 2012 09:55:28 +0800
From:	Wen Congyang <wency@...fujitsu.com>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
CC:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>, 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, cl@...ux.com, minchan.kim@...il.com,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 5/10] memory-hotplug : memory-hotplug: check page type
 in get_page_bootmem

At 10/19/2012 08:49 AM, Yasuaki Ishimatsu Wrote:
> Hi Kosaki,
> 
> Sorry for late reply.
> 
> 2012/10/13 4:28, KOSAKI Motohiro wrote:
>> On Thu, Oct 4, 2012 at 10:32 PM, Yasuaki Ishimatsu
>> <isimatu.yasuaki@...fujitsu.com> wrote:
>>> The function get_page_bootmem() may be called more than one time to
>>> the same
>>> page. There is no need to set page's type, private if the function is
>>> not
>>> the first time called to the page.
>>>
>>> Note: the patch is just optimization and does not fix any problem.
>>>
>>> CC: David Rientjes <rientjes@...gle.com>
>>> CC: Jiang Liu <liuj97@...il.com>
>>> CC: Len Brown <len.brown@...el.com>
>>> CC: Christoph Lameter <cl@...ux.com>
>>> Cc: Minchan Kim <minchan.kim@...il.com>
>>> CC: Andrew Morton <akpm@...ux-foundation.org>
>>> CC: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
>>> CC: Wen Congyang <wency@...fujitsu.com>
>>> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
>>> ---
>>>   mm/memory_hotplug.c |   15 +++++++++++----
>>>   1 file changed, 11 insertions(+), 4 deletions(-)
>>>
>>> Index: linux-3.6/mm/memory_hotplug.c
>>> ===================================================================
>>> --- linux-3.6.orig/mm/memory_hotplug.c  2012-10-04 18:29:58.284676075
>>> +0900
>>> +++ linux-3.6/mm/memory_hotplug.c       2012-10-04 18:30:03.454680542
>>> +0900
>>> @@ -95,10 +95,17 @@ static void release_memory_resource(stru
>>>   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 I understand correctly, page->lru.next might be uninitialized yet.
> 
> Ah yes. I was misunderstanding...
> 
> Hi Wen,
> 
> When you update the physical hot remove patch-set, please drop the patch.

OK

Thanks
Wen Congyang

> 
> Thanks,
> Yasuaki Ishimatsu   
>> Moreover, I have no seen any good effect in this patch. I don't
>> understand
>> why we need to increase code complexity.
>>
>>
>>
>>> +       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);
>>>   }
>>>
>>>   /* reference to __meminit __free_pages_bootmem is valid
>>>
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> 
> 
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