linux-kernel - [PATCH v3 5/5] mm/huge_memory.c: don't discard hugepage if other processes are mapping it

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Date:   Tue, 11 May 2021 21:48:57 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     <akpm@...ux-foundation.org>
CC:     <ziy@...dia.com>, <william.kucharski@...cle.com>,
        <willy@...radead.org>, <yang.shi@...ux.alibaba.com>,
        <aneesh.kumar@...ux.ibm.com>, <rcampbell@...dia.com>,
        <songliubraving@...com>, <kirill.shutemov@...ux.intel.com>,
        <riel@...riel.com>, <hannes@...xchg.org>, <minchan@...nel.org>,
        <hughd@...gle.com>, <adobriyan@...il.com>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <linux-fsdevel@...r.kernel.org>, <linmiaohe@...wei.com>
Subject: [PATCH v3 5/5] mm/huge_memory.c: don't discard hugepage if other processes are mapping it

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")
Reviewed-by: Yang Shi <shy828301@...il.com>
Signed-off-by: Miaohe Lin <linmiaohe@...wei.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 b8e67332806f..24647fe076b8 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1610,7 +1610,7 @@ 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