[PATCH] mm: bio_alloc never fails when set GFP_NOIO, GFP_KERNEL

From: Xianting Tian
Date: Tue Oct 20 2020 - 23:21:55 EST


bio_alloc with __GFP_DIRECT_RECLAIM(which is included in GFP_NOIO,
GFP_KERNEL) never fails, as stated in the comments of bio_alloc_bioset.

So we can remove multiple unneeded null checks of bio_alloc and simplify
the code.

We have done it in fs/ext4/readpage.c, fs/ext4/page-io.c, fs/direct-io.c,
and so forth.

Signed-off-by: Xianting Tian <tian.xianting@xxxxxxx>
---
mm/page_io.c | 31 +++++++++++--------------------
1 file changed, 11 insertions(+), 20 deletions(-)

diff --git a/mm/page_io.c b/mm/page_io.c
index e485a6e8a..9215bb356 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -30,18 +30,20 @@ static struct bio *get_swap_bio(gfp_t gfp_flags,
struct page *page, bio_end_io_t end_io)
{
struct bio *bio;
+ struct block_device *bdev;

+ /*
+ * bio_alloc will _always_ be able to allocate a bio if
+ * __GFP_DIRECT_RECLAIM is set, see comments for bio_alloc_bioset().
+ */
bio = bio_alloc(gfp_flags, 1);
- if (bio) {
- struct block_device *bdev;
+ bio->bi_iter.bi_sector = map_swap_page(page, &bdev);
+ bio_set_dev(bio, bdev);
+ bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9;
+ bio->bi_end_io = end_io;

- bio->bi_iter.bi_sector = map_swap_page(page, &bdev);
- bio_set_dev(bio, bdev);
- bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9;
- bio->bi_end_io = end_io;
+ bio_add_page(bio, page, thp_size(page), 0);

- bio_add_page(bio, page, thp_size(page), 0);
- }
return bio;
}

@@ -351,19 +353,13 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,

ret = 0;
bio = get_swap_bio(GFP_NOIO, page, end_write_func);
- if (bio == NULL) {
- set_page_dirty(page);
- unlock_page(page);
- ret = -ENOMEM;
- goto out;
- }
bio->bi_opf = REQ_OP_WRITE | REQ_SWAP | wbc_to_write_flags(wbc);
bio_associate_blkg_from_page(bio, page);
count_swpout_vm_event(page);
set_page_writeback(page);
unlock_page(page);
submit_bio(bio);
-out:
+
return ret;
}

@@ -416,11 +412,6 @@ int swap_readpage(struct page *page, bool synchronous)

ret = 0;
bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
- if (bio == NULL) {
- unlock_page(page);
- ret = -ENOMEM;
- goto out;
- }
disk = bio->bi_disk;
/*
* Keep this task valid during swap readpage because the oom killer may
--
2.17.1