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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 6861428921 ("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 6861428921 ("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 6861428921
("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: 6861428921 ("block: always define BIO_MAX_PAGES as 256")
Signed-off-by: "Huang, Ying" <>
Reviewed-by: Ming Lei <>
Cc: Michal Hocko <>
Cc: Johannes Weiner <>
Cc: Hugh Dickins <>
Cc: Minchan Kim <>
Cc: Rik van Riel <>
Cc: Daniel Jordan <>
Cc: Jens Axboe <>
Cc: <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
Huang Ying 2 years ago
committed by Linus Torvalds
  1. 7


@ -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;