From: Miaohe Lin <linmiaohe@xxxxxxxxxx> Subject: 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@xxxxxxxxxx Fixes: b8d3c4c3009d ("mm/huge_memory.c: don't split THP page when MADV_FREE syscall is called") Reviewed-by: Yang Shi <shy828301@xxxxxxxxx> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx> Cc: "Aneesh Kumar K . V" <aneesh.kumar@xxxxxxxxxxxxx> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx> Cc: David Hildenbrand <david@xxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Cc: Ralph Campbell <rcampbell@xxxxxxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxxx> Cc: Song Liu <songliubraving@xxxxxx> Cc: William Kucharski <william.kucharski@xxxxxxxxxx> Cc: Zi Yan <ziy@xxxxxxxxxx> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/huge_memory.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/huge_memory.c~mm-huge_memoryc-dont-discard-hugepage-if-other-processes-are-mapping-it +++ a/mm/huge_memory.c @@ -1613,7 +1613,7 @@ bool madvise_free_huge_pmd(struct mmu_ga * 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)) _
