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 09:49:24 +0900
From:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	<wency@...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>,
	<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

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.

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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