Re: [PATCH] mm: Fix for PG_reserved page flag clearing

[Masayoshi Mizuma <msys.mizuma@gmail.com>]

Hello Michal, 

Mon, 19 Feb 2018 18:19:16 +0100 Michal Hocko wrote:
> On Mon 19-02-18 12:06:14, Masayoshi Mizuma wrote:
>> From: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
>>
>> struct page is inizialized as zero in __init_single_page().
>> If the page is offlined page, PG_reserved flag is set in early boot
>> time before __init_single_page(), so we should not clear the flag.
>>
>> The real problem is that we can not online the offlined page
>> through following sysfs operation because offlined page is
>> expected PG_reserved flag is set. 
>> It is not needed the initialization, so remove it simply.
>>
>>   Code:
>>
>>   static int online_pages_range(unsigned long start_pfn, 
>>   ...
>>           if (PageReserved(pfn_to_page(start_pfn))) <= HERE!!
>>                   for (i = 0; i < nr_pages; i++) {
>>                           page = pfn_to_page(start_pfn + i);
>>                           (*online_page_callback)(page);
>>                           onlined_pages++;
>>   sysfs operation:
>>
>>   # echo online > /sys/devices/system/node/node2/memory12288/online
>>   # cat /sys/devices/system/node/node2/memory12288/online 
>>   1
>>   # cat /sys/devices/system/node/node2/meminfo 
>>   Node 2 MemTotal:              0 kB
> 
> Nack. The patch is simply wrong. We do need to zero page for the boot
> pages. I believe the fix you are looking for is 9bb5a391f9a5 ("mm,
> memory_hotplug: fix memmap initialization"). Or do you still see a
> problem with this patch applied?

I have confirmed the problem is fixed by your patch 9bb5a391f9a5.
(I had tested it in 4.15.2, so I did not notice your patch, sorry)

Thank you for the fix!

- Masayoshi

> 
>> Fixes: f7f99100d8d9 ("mm: stop zeroing memory during allocation in vmemmap")
>> Signed-off-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
>> ---
>>  mm/page_alloc.c | 1 -
>>  1 file changed, 1 deletion(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 76c9688..3260cd2 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -1179,7 +1179,6 @@ static void free_one_page(struct zone *zone,
>>  static void __meminit __init_single_page(struct page *page, unsigned long pfn,
>>  				unsigned long zone, int nid)
>>  {
>> -	mm_zero_struct_page(page);
>>  	set_page_links(page, zone, nid, pfn);
>>  	init_page_count(page);
>>  	page_mapcount_reset(page);
>> -- 
>> 2.16.1
>>
>> - Masayoshi
> 

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