On Wed, 21 Oct 2020 11:11:28 +0800 Xianting Tian <tian.xianting@xxxxxxx> wrote:
> 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.
>
(cc Jens)
> --- 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
I'm reluctant to remove these checks - yours is a fairly subtle
discovery and things might change in the future. Intentionally or
otherwise!
