[016/192] mm/huge_memory.c: don't discard hugepage if other processes are mapping it

Commit Message

Andrew Morton July 1, 2021, 1:47 a.m. UTC

From: Miaohe Lin <[e-mail]>
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/[e-mail]
Fixes: b8d3c4c3009d ("mm/huge_memory.c: don't split THP page when MADV_FREE syscall is called")
Reviewed-by: Yang Shi <[e-mail]>
Signed-off-by: Miaohe Lin <[e-mail]>
Cc: Alexey Dobriyan <[e-mail]>
Cc: "Aneesh Kumar K . V" <[e-mail]>
Cc: Anshuman Khandual <[e-mail]>
Cc: David Hildenbrand <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Kirill A. Shutemov <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: Minchan Kim <[e-mail]>
Cc: Ralph Campbell <[e-mail]>
Cc: Rik van Riel <[e-mail]>
Cc: Song Liu <[e-mail]>
Cc: William Kucharski <[e-mail]>
Cc: Zi Yan <[e-mail]>
Cc: Mike Kravetz <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/huge_memory.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Patch

--- 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))