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

[David Hildenbrand]

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@xxxxxxxxxxxxxx>
> ---
>   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