From: Hugh Dickins hughd@google.com
commit bd55b0c2d64e84a75575f548a33a3dfecc135b65 upstream.
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@linu...
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: 9a73f61bdb8a ("thp, mlock: do not mlock PTE-mapped file huge pages") Signed-off-by: Hugh Dickins hughd@google.com Reviewed-by: Yang Shi shy828301@gmail.com Cc: "Kirill A. Shutemov" kirill.shutemov@linux.intel.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/rmap.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
diff --git a/mm/rmap.c b/mm/rmap.c index 9e27f9f038d3..444d0d958aff 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -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);