Hi Huang Ying,
On Mon, Jun 24, 2019 at 10:23:36AM +0800, Huang, Ying wrote:
> From: Huang Ying <ying.huang@xxxxxxxxx>
>
> 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.huang@xxxxxxxxx>
> Cc: 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>
> ---
> 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.
Could you share me one test case for reproducing it?
> - 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;
Actually the above code can be simplified as:
diff --git a/mm/page_io.c b/mm/page_io.c
index 2e8019d0e048..c20b4189d0a1 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -29,7 +29,7 @@
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);
+ int nr = hpage_nr_pages(page);
struct bio *bio;
bio = bio_alloc(gfp_flags, nr);
@@ -41,8 +41,7 @@ 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(bio, page, PAGE_SIZE * nr, 0);
VM_BUG_ON(bio->bi_iter.bi_size != PAGE_SIZE * nr);
}
return bio;
Thanks,
Ming
