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    Subject[PATCH 5.13 766/800] mm/huge_memory.c: dont discard hugepage if other processes are mapping it
    Date
    From: Miaohe Lin <linmiaohe@huawei.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@gmail.com>
    Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
    Cc: Alexey Dobriyan <adobriyan@gmail.com>
    Cc: "Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>
    Cc: Anshuman Khandual <anshuman.khandual@arm.com>
    Cc: David Hildenbrand <david@redhat.com>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Cc: Matthew Wilcox <willy@infradead.org>
    Cc: Minchan Kim <minchan@kernel.org>
    Cc: Ralph Campbell <rcampbell@nvidia.com>
    Cc: Rik van Riel <riel@surriel.com>
    Cc: Song Liu <songliubraving@fb.com>
    Cc: William Kucharski <william.kucharski@oracle.com>
    Cc: Zi Yan <ziy@nvidia.com>
    Cc: Mike Kravetz <mike.kravetz@oracle.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Sasha Levin <sashal@kernel.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 2496f787a829..8857ef1543eb 100644
    --- a/mm/huge_memory.c
    +++ b/mm/huge_memory.c
    @@ -1613,7 +1613,7 @@ 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


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