linux-kernel - [PATCH 4.19 222/421] mm/huge_memory.c: dont discard hugepage if other processes are mapping it

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Message-Id: <20210719144954.033617970@linuxfoundation.org>
Date:   Mon, 19 Jul 2021 16:50:33 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Yang Shi <shy828301@...il.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        David Hildenbrand <david@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        Minchan Kim <minchan@...nel.org>,
        Ralph Campbell <rcampbell@...dia.com>,
        Rik van Riel <riel@...riel.com>,
        Song Liu <songliubraving@...com>,
        William Kucharski <william.kucharski@...cle.com>,
        Zi Yan <ziy@...dia.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 222/421] mm/huge_memory.c: dont discard hugepage if other processes are mapping it

From: Miaohe Lin <linmiaohe@...wei.com>

[ Upstream commit babbbdd08af98a59089334eb3effbed5a7a0cf7f ]

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.

Link: https://lkml.kernel.org/r/20210511134857.1581273-6-linmiaohe@huawei.com
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>
Cc: Alexey Dobriyan <adobriyan@...il.com>
Cc: "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>
Cc: Anshuman Khandual <anshuman.khandual@....com>
Cc: David Hildenbrand <david@...hat.com>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Minchan Kim <minchan@...nel.org>
Cc: Ralph Campbell <rcampbell@...dia.com>
Cc: Rik van Riel <riel@...riel.com>
Cc: Song Liu <songliubraving@...com>
Cc: William Kucharski <william.kucharski@...cle.com>
Cc: Zi Yan <ziy@...dia.com>
Cc: Mike Kravetz <mike.kravetz@...cle.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 4400957d8e4e..800d7de32af8 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1692,7 +1692,7 @@ 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))
-- 
2.30.2