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

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Message-ID: <dd242708-e3f5-ab9f-64d4-9efe3b7168ce@redhat.com>
Date:   Wed, 28 Apr 2021 16:54:59 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Ding Hui <dinghui@...gfor.com.cn>, 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 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?


-- 
Thanks,

David / dhildenb