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

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Message-Id: <20210421020426.5914-1-dinghui@sangfor.com.cn>
Date:   Wed, 21 Apr 2021 10:04:26 +0800
From:   Ding Hui <dinghui@...gfor.com.cn>
To:     akpm@...ux-foundation.org, naoya.horiguchi@....com,
        osalvador@...e.de
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Ding Hui <dinghui@...gfor.com.cn>
Subject: [RFC PATCH] mm/page_alloc: fix counting of free pages after take off from buddy

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;
 		}
-- 
2.17.1