linux-kernel - Re: [RFC PATCH] mm/page_alloc: fix counting of free pages after take off from buddy

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Date:   Fri, 30 Apr 2021 17:43:40 +0800
From:   Ding Hui <dinghui@...gfor.com.cn>
To:     David Hildenbrand <david@...hat.com>, akpm@...ux-foundation.org,
        naoya.horiguchi@....com, osalvador@...e.de
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] mm/page_alloc: fix counting of free pages after take
 off from buddy

On 2021/4/28 22:54, David Hildenbrand wrote:
> On 21.04.21 04:04, Ding Hui wrote:
>> Recently we found there is a lot MemFree left in /proc/meminfo after
>> do a lot of pages soft offline.
>>
>> I think it's incorrect since NR_FREE_PAGES should not contain HWPoison 
>> pages.
>> After take_page_off_buddy, the page is no longer belong to buddy
>> allocator, and will not be used any more, but we maybe missed accounting
>> NR_FREE_PAGES in this situation.
>>
>> Signed-off-by: Ding Hui <dinghui@...gfor.com.cn>
>> ---
>>   mm/page_alloc.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index cfc72873961d..8d65b62784d8 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -8947,6 +8947,7 @@ bool take_page_off_buddy(struct page *page)
>>               del_page_from_free_list(page_head, zone, page_order);
>>               break_down_buddy_pages(zone, page_head, page, 0,
>>                           page_order, migratetype);
>> +            __mod_zone_page_state(zone, NR_FREE_PAGES, -1);
>>               ret = true;
>>               break;
>>           }
>>
> 
> Should this use __mod_zone_freepage_state() instead?
> 

Yes, you're right.
I'll use it in v2.

-- 
Thanks,
- Ding Hui