[PATCH 3/3] Revert "mm: remove get_swap_bio"

[Chris Wilson]

This reverts commit 48d15436fde6feebcded7bd0fdc8ea4a9181b8fa.
---
 include/linux/swap.h |  1 +
 mm/page_io.c         | 45 +++++++++++++++++++++++++++++++-------------
 mm/swapfile.c        | 10 ++++++++++
 3 files changed, 43 insertions(+), 13 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 32f665b1ee85..71166bc10d17 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -472,6 +472,7 @@ 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);
diff --git a/mm/page_io.c b/mm/page_io.c
index 485fa5cca4a2..64466571c700 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -26,6 +26,25 @@
 #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);
@@ -342,13 +361,13 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
 		return 0;
 	}
 
-	bio = bio_alloc(GFP_NOIO, 1);
-	bio_set_dev(bio, sis->bdev);
-	bio->bi_iter.bi_sector = swap_page_sector(page);
+	bio = get_swap_bio(GFP_NOIO, page, end_write_func);
+	if (bio == NULL) {
+		set_page_dirty(page);
+		unlock_page(page);
+		return -ENOMEM;
+	}
 	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);
@@ -408,18 +427,18 @@ int swap_readpage(struct page *page, bool synchronous)
 	}
 
 	ret = 0;
-	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);
-
+	bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
+	if (bio == NULL) {
+		unlock_page(page);
+		ret = -ENOMEM;
+		goto out;
+	}
 	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);
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 7b9a033783f8..7a2ca11706db 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2302,6 +2302,16 @@ 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
  */
-- 
2.20.1