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.

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>

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 7972baa..7ccea3e 100644 (file)
--- 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))