Commit bd55b0c2 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

mm/thp: ClearPageDoubleMap in first page_add_file_rmap() 

PageDoubleMap is maintained differently for anon and for shmem+file: the
shmem+file one was never cleared, because a safe place to do so could
not be found; so it would blight future use of the cached hugepage until
evicted.

See https://lore.kernel.org/lkml/1571938066-29031-1-git-send-email-yang.shi@linux.alibaba.com/

But page_add_file_rmap() does provide a safe place to do so (though later
than one might wish): allowing testing to return to an initial state
without a damaging drop_caches.

Link: https://lkml.kernel.org/r/61c5cf99-a962-9a25-597a-53ab1bd8fbc0@google.com


Fixes: 9a73f61b ("thp, mlock: do not mlock PTE-mapped file huge pages")
Signed-off-by: default avatarHugh Dickins <hughd@google.com>
Reviewed-by: default avatarYang Shi <shy828301@gmail.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 734c1570

mm/rmap.c

+11 −0
Original line number Diff line number Diff line
@@ -1252,6 +1252,17 @@ void page_add_file_rmap(struct page *page, bool compound) 
		}

		if (!atomic_inc_and_test(compound_mapcount_ptr(page)))

			goto out;



		/*

		 * It is racy to ClearPageDoubleMap in page_remove_file_rmap();

		 * but page lock is held by all page_add_file_rmap() compound

		 * callers, and SetPageDoubleMap below warns if !PageLocked:

		 * so here is a place that DoubleMap can be safely cleared.

		 */

		VM_WARN_ON_ONCE(!PageLocked(page));

		if (nr == nr_pages && PageDoubleMap(page))

			ClearPageDoubleMap(page);



		if (PageSwapBacked(page))

			__mod_lruvec_page_state(page, NR_SHMEM_PMDMAPPED,

						nr_pages);