From: Huang Ying <ying.huang@xxxxxxxxx>
Subject: mm, swap: fix THP swap out
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.
Link: http://lkml.kernel.org/r/20190624075515.31040-1-ying.huang@xxxxxxxxx
Fixes: 6861428921b5 ("block: always define BIO_MAX_PAGES as 256")
Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_io.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
--- a/mm/page_io.c~mm-swap-fix-thp-swap-out
+++ a/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 gf
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;
}
_
