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

[Xianting Tian]

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.xiant...@h3c.com>
---
 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