On Mon, Jun 24, 2019 at 12:44:41PM +0800, Huang, Ying wrote: > Ming Lei <[email protected]> writes: > > > Hi Huang Ying, > > > > On Mon, Jun 24, 2019 at 10:23:36AM +0800, Huang, Ying wrote: > >> From: Huang Ying <[email protected]> > >> > >> 0-Day test system reported some OOM regressions for several > >> THP (Transparent Huge Page) swap test cases. These regressions are > >> bisected to 6861428921b5 ("block: always define BIO_MAX_PAGES as > >> 256"). In the commit, BIO_MAX_PAGES is set to 256 even when THP swap > >> is enabled. So the bio_alloc(gfp_flags, 512) in get_swap_bio() may > >> fail when swapping out THP. That causes the OOM. > >> > >> As in the patch description of 6861428921b5 ("block: always define > >> BIO_MAX_PAGES as 256"), THP swap should use multi-page bvec to write > >> THP to swap space. So the issue is fixed via doing that in > >> get_swap_bio(). > >> > >> BTW: I remember I have checked the THP swap code when > >> 6861428921b5 ("block: always define BIO_MAX_PAGES as 256") was merged, > >> and thought the THP swap code needn't to be changed. But apparently, > >> I was wrong. I should have done this at that time. > >> > >> Fixes: 6861428921b5 ("block: always define BIO_MAX_PAGES as 256") > >> Signed-off-by: "Huang, Ying" <[email protected]> > >> Cc: Ming Lei <[email protected]> > >> Cc: Michal Hocko <[email protected]> > >> Cc: Johannes Weiner <[email protected]> > >> Cc: Hugh Dickins <[email protected]> > >> Cc: Minchan Kim <[email protected]> > >> Cc: Rik van Riel <[email protected]> > >> Cc: Daniel Jordan <[email protected]> > >> --- > >> mm/page_io.c | 7 ++----- > >> 1 file changed, 2 insertions(+), 5 deletions(-) > >> > >> diff --git a/mm/page_io.c b/mm/page_io.c > >> index 2e8019d0e048..4ab997f84061 100644 > >> --- a/mm/page_io.c > >> +++ b/mm/page_io.c > >> @@ -29,10 +29,9 @@ > >> static struct bio *get_swap_bio(gfp_t gfp_flags, > >> struct page *page, bio_end_io_t end_io) > >> { > >> - int i, nr = hpage_nr_pages(page); > >> struct bio *bio; > >> > >> - bio = bio_alloc(gfp_flags, nr); > >> + bio = bio_alloc(gfp_flags, 1); > >> if (bio) { > >> struct block_device *bdev; > >> > >> @@ -41,9 +40,7 @@ static struct bio *get_swap_bio(gfp_t gfp_flags, > >> bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9; > >> bio->bi_end_io = end_io; > >> > >> - for (i = 0; i < nr; i++) > >> - bio_add_page(bio, page + i, PAGE_SIZE, 0); > > > > bio_add_page() supposes to work, just wondering why it doesn't recently. > > Yes. Just checked and bio_add_page() works too. I should have used > that. The problem isn't bio_add_page(), but bio_alloc(), because nr == > 512 > 256, mempool cannot be used during swapout, so swapout will fail.
Then we can pass 1 to bio_alloc(), together with single bio_add_page() for making the code more readable. thanks, Ming
