Subject: Re: [RFC v9 PATCH 13/21] memory-hotplug: check page type in get_page_bootmem

From: Yasuaki Ishimatsu <[email-masked]>
Date: Mon, 1 Oct 2012 12:03:01 +0900

Hi Chen,

2012/09/29 11:15, Ni zhan Chen wrote:
> On 09/05/2012 05:25 PM, [email-masked] wrote:
>> From: Yasuaki Ishimatsu <[email-masked]>
>>
>> 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.
>
> Hi Yasuaki,
>
> this patch is reasonable to me. I have another question associated to get_page_bootmem(), the question is from another fujitsu guy's patch changelog [commit : 04753278769f3], the changelog said  that:
>
>   1) When the memmap of removing section is allocated on other
>       section by bootmem, it should/can be free.
>   2) When the memmap of removing section is allocated on the
>       same section, it shouldn't be freed. Because the section has to be
>       logical memory offlined already and all pages must be isolated against
>       page allocater. If it is freed, page allocator may use it which will
>       be removed physically soon.
>
> but I don't see his patch guarantee 2), it means that his patch doesn't guarantee the memmap of removing section which is allocated on other section by bootmem doesn't be freed. Hopefully get your explaination in details, thanks in advance. :-)

In my understanding, the patch does not guarantee it.
Please see [commit : 0c0a4a517a31e]. free_map_bootmem() in the commit
guarantees it.

Thanks,
Yasuaki Ishimatsu

>
>>
>> CC: David Rientjes <[email-masked]>
>> CC: Jiang Liu <[email-masked]>
>> CC: Len Brown <[email-masked]>
>> CC: Benjamin Herrenschmidt <[email-masked]>
>> CC: Paul Mackerras <[email-masked]>
>> CC: Christoph Lameter <[email-masked]>
>> Cc: Minchan Kim <[email-masked]>
>> CC: Andrew Morton <[email-masked]>
>> CC: KOSAKI Motohiro <[email-masked]>
>> CC: Wen Congyang <[email-masked]>
>> Signed-off-by: Yasuaki Ishimatsu <[email-masked]>
>> ---
>>   mm/memory_hotplug.c |   15 +++++++++++----
>>   1 files changed, 11 insertions(+), 4 deletions(-)
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index d736df3..26a5012 100644
>> --- 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);
>>   }
>>   /* reference to __meminit __free_pages_bootmem is valid
>