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/[email protected]
Fixes: 6861428921b5 ("block: always define BIO_MAX_PAGES as 256")
Signed-off-by: "Huang, Ying" <[email protected]>
Reviewed-by: 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]>
Cc: Jens Axboe <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions