linux-kernel - [Resend PATCH 5/6] mm/thp: remove code path which never got into

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Message-Id: <1597144232-11370-5-git-send-email-alex.shi@linux.alibaba.com>
Date:   Tue, 11 Aug 2020 19:10:31 +0800
From:   Alex Shi <alex.shi@...ux.alibaba.com>
To:     akpm@...ux-foundation.org
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Johannes Weiner <hannes@...xchg.org>,
        Matthew Wilcox <willy@...radead.org>,
        Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [Resend PATCH 5/6] mm/thp: remove code path which never got into

split_huge_page() will never call on a page which isn't on lru list, so
this code never got a chance to run, and should not be run, to add tail
pages on a lru list which head page isn't there.

Although the bug was never triggered, it'better be removed for code
correctness, and add a warn for unexpected calling.

Signed-off-by: Alex Shi <alex.shi@...ux.alibaba.com>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Cc: Kirill A. Shutemov <kirill@...temov.name>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org
---
 mm/huge_memory.c | 13 ++-----------
 1 file changed, 2 insertions(+), 11 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 8cecd39bd8b7..d55e3006c63f 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2332,17 +2332,8 @@ static void lru_add_page_tail(struct page *head, struct page *page_tail,
 		/* page reclaim is reclaiming a huge page */
 		get_page(page_tail);
 		list_add_tail(&page_tail->lru, list);
-	} else {
-		/*
-		 * Head page has not yet been counted, as an hpage,
-		 * so we must account for each subpage individually.
-		 *
-		 * Put page_tail on the list at the correct position
-		 * so they all end up in order.
-		 */
-		add_page_to_lru_list_tail(page_tail, lruvec,
-					  page_lru(page_tail));
-	}
+	} else
+		VM_WARN_ON(!PageLRU(head));
 }
 
 static void __split_huge_page_tail(struct page *head, int tail,
-- 
1.8.3.1