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From:   Miaohe Lin <linmiaohe@huawei.com>
To:     <akpm@linux-foundation.org>
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        <willy@infradead.org>, <yang.shi@linux.alibaba.com>,
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        <linmiaohe@huawei.com>
Subject: [PATCH 5/5] mm/huge_memory.c: don't discard hugepage if other processes are mapping it
Date:   Tue, 27 Apr 2021 21:32:14 +0800
Message-ID: <20210427133214.2270207-6-linmiaohe@huawei.com>
In-Reply-To: <20210427133214.2270207-1-linmiaohe@huawei.com>
References: <20210427133214.2270207-1-linmiaohe@huawei.com>
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If other processes are mapping any other subpages of the hugepage, i.e. in
pte-mapped thp case, page_mapcount() will return 1 incorrectly. Then we
would discard the page while other processes are still mapping it. Fix it
by using total_mapcount() which can tell whether other processes are still
mapping it.

Fixes: b8d3c4c3009d ("mm/huge_memory.c: don't split THP page when MADV_FREE syscall is called")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 mm/huge_memory.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index f652be6ecca3..d14fecb8cd00 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1604,7 +1604,7 @@ bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 	 * If other processes are mapping this page, we couldn't discard
 	 * the page unless they all do MADV_FREE so let's skip the page.
 	 */
-	if (page_mapcount(page) != 1)
+	if (total_mapcount(page) != 1)
 		goto out;
 
 	if (!trylock_page(page))
-- 
2.23.0