From: Huang Ying <ying.hu...@intel.com> 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" <ying.hu...@intel.com> Cc: Ming Lei <ming....@redhat.com> Cc: Michal Hocko <mho...@kernel.org> Cc: Johannes Weiner <han...@cmpxchg.org> Cc: Hugh Dickins <hu...@google.com> Cc: Minchan Kim <minc...@kernel.org> Cc: Rik van Riel <r...@redhat.com> Cc: Daniel Jordan <daniel.m.jor...@oracle.com> Changelogs: V2: - Replace __bio_add_page() with bio_add_page() per Ming's comments. --- 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..189415852077 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); - VM_BUG_ON(bio->bi_iter.bi_size != PAGE_SIZE * nr); + bio_add_page(bio, page, PAGE_SIZE * hpage_nr_pages(page), 0); } return bio; } -- 2.20.1