mm: remove get_swap_bio

Just reuse the block_device and sector from the swap_info structure,
just as used by the SWP_SYNCHRONOUS path.  Also remove the checks for
NULL returns from bio_alloc as that can't happen for sleeping
allocations.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Acked-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/swap.h

@@ -468,7 +468,6 @@ extern int free_swap_and_cache(swp_entry_t);
 int swap_type_of(dev_t device, sector_t offset);
 int find_first_swap(dev_t *device);
 extern unsigned int count_swap_pages(int, int);
-extern sector_t map_swap_page(struct page *, struct block_device **);
 extern sector_t swapdev_block(int, pgoff_t);
 extern int page_swapcount(struct page *);
 extern int __swap_count(swp_entry_t entry);

mm/page_io.c

@@ -26,25 +26,6 @@
 #include <linux/uio.h>
 #include <linux/sched/task.h>
 
-static struct bio *get_swap_bio(gfp_t gfp_flags,
-				struct page *page, bio_end_io_t end_io)
-{
-	struct bio *bio;
-
-	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_add_page(bio, page, thp_size(page), 0);
-	}
-	return bio;
-}
-
 void end_swap_bio_write(struct bio *bio)
 {
 	struct page *page = bio_first_page_all(bio);
@@ -361,13 +342,13 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
 		return 0;
 	}
 
-	bio = get_swap_bio(GFP_NOIO, page, end_write_func);
-	if (bio == NULL) {
-		set_page_dirty(page);
-		unlock_page(page);
-		return -ENOMEM;
-	}
+	bio = bio_alloc(GFP_NOIO, 1);
+	bio_set_dev(bio, sis->bdev);
+	bio->bi_iter.bi_sector = swap_page_sector(page);
 	bio->bi_opf = REQ_OP_WRITE | REQ_SWAP | wbc_to_write_flags(wbc);
+	bio->bi_end_io = end_write_func;
+	bio_add_page(bio, page, thp_size(page), 0);
+
 	bio_associate_blkg_from_page(bio, page);
 	count_swpout_vm_event(page);
 	set_page_writeback(page);
@@ -427,18 +408,18 @@ 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;
-	}
+	bio = bio_alloc(GFP_KERNEL, 1);
+	bio_set_dev(bio, sis->bdev);
+	bio->bi_opf = REQ_OP_READ;
+	bio->bi_iter.bi_sector = swap_page_sector(page);
+	bio->bi_end_io = end_swap_bio_read;
+	bio_add_page(bio, page, thp_size(page), 0);
+
 	disk = bio->bi_bdev->bd_disk;
 	/*
 	 * Keep this task valid during swap readpage because the oom killer may
 	 * attempt to access it in the page fault retry time check.
 	 */
-	bio_set_op_attrs(bio, REQ_OP_READ, 0);
 	if (synchronous) {
 		bio->bi_opf |= REQ_HIPRI;
 		get_task_struct(current);

mm/swapfile.c

@@ -2301,16 +2301,6 @@ static sector_t map_swap_entry(swp_entry_t entry, struct block_device **bdev)
 	return se->start_block + (offset - se->start_page);
 }
 
-/*
- * Returns the page offset into bdev for the specified page's swap entry.
- */
-sector_t map_swap_page(struct page *page, struct block_device **bdev)
-{
-	swp_entry_t entry;
-	entry.val = page_private(page);
-	return map_swap_entry(entry, bdev);
-}
-
 /*
  * Free all of a swapdev's extent information
  */