zram: pass a page to read_from_bdev

read_from_bdev always reads a whole page, so pass a page to it instead of
the bvec and remove the now pointless zram_bvec_read_from_bdev wrapper.

Link: https://lkml.kernel.org/r/20230411171459.567614-15-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

drivers/block/zram/zram_drv.c

@@ -588,7 +588,7 @@ static void zram_page_end_io(struct bio *bio)
 /*
  * Returns 1 if the submission is successful.
  */
-static int read_from_bdev_async(struct zram *zram, struct bio_vec *bvec,
+static int read_from_bdev_async(struct zram *zram, struct page *page,
 			unsigned long entry, struct bio *parent)
 {
 	struct bio *bio;
@@ -599,7 +599,7 @@ static int read_from_bdev_async(struct zram *zram, struct bio_vec *bvec,
 		return -ENOMEM;
 
 	bio->bi_iter.bi_sector = entry * (PAGE_SIZE >> 9);
-	if (!bio_add_page(bio, bvec->bv_page, bvec->bv_len, bvec->bv_offset)) {
+	if (!bio_add_page(bio, page, PAGE_SIZE, 0)) {
 		bio_put(bio);
 		return -EIO;
 	}
@@ -795,7 +795,7 @@ struct zram_work {
 	struct zram *zram;
 	unsigned long entry;
 	struct bio *bio;
-	struct bio_vec bvec;
+	struct page *page;
 };
 
 static void zram_sync_read(struct work_struct *work)
@@ -805,20 +805,20 @@ static void zram_sync_read(struct work_struct *work)
 	unsigned long entry = zw->entry;
 	struct bio *bio = zw->bio;
 
-	read_from_bdev_async(zram, &zw->bvec, entry, bio);
+	read_from_bdev_async(zram, zw->page, entry, bio);
 }
 
 /*
  * Block layer want one ->submit_bio to be active at a time, so if we use
  * chained IO with parent IO in same context, it's a deadlock. To avoid that,
  * use a worker thread context.
  */
-static int read_from_bdev_sync(struct zram *zram, struct bio_vec *bvec,
+static int read_from_bdev_sync(struct zram *zram, struct page *page,
 				unsigned long entry, struct bio *bio)
 {
 	struct zram_work work;
 
-	work.bvec = *bvec;
+	work.page = page;
 	work.zram = zram;
 	work.entry = entry;
 	work.bio = bio;
@@ -831,20 +831,20 @@ static int read_from_bdev_sync(struct zram *zram, struct bio_vec *bvec,
 	return 1;
 }
 
-static int read_from_bdev(struct zram *zram, struct bio_vec *bvec,
+static int read_from_bdev(struct zram *zram, struct page *page,
 			unsigned long entry, struct bio *parent, bool sync)
 {
 	atomic64_inc(&zram->stats.bd_reads);
 	if (sync) {
 		if (WARN_ON_ONCE(!IS_ENABLED(ZRAM_PARTIAL_IO)))
 			return -EIO;
-		return read_from_bdev_sync(zram, bvec, entry, parent);
+		return read_from_bdev_sync(zram, page, entry, parent);
 	}
-	return read_from_bdev_async(zram, bvec, entry, parent);
+	return read_from_bdev_async(zram, page, entry, parent);
 }
 #else
 static inline void reset_bdev(struct zram *zram) {};
-static int read_from_bdev(struct zram *zram, struct bio_vec *bvec,
+static int read_from_bdev(struct zram *zram, struct page *page,
 			unsigned long entry, struct bio *parent, bool sync)
 {
 	return -EIO;
@@ -1328,20 +1328,6 @@ static void zram_free_page(struct zram *zram, size_t index)
 		~(1UL << ZRAM_LOCK | 1UL << ZRAM_UNDER_WB));
 }
 
-/*
- * Reads a page from the writeback devices. Corresponding ZRAM slot
- * should be unlocked.
- */
-static int zram_bvec_read_from_bdev(struct zram *zram, struct page *page,
-				    u32 index, struct bio *bio, bool partial_io)
-{
-	struct bio_vec bvec;
-
-	bvec_set_page(&bvec, page, PAGE_SIZE, 0);
-	return read_from_bdev(zram, &bvec, zram_get_element(zram, index), bio,
-			      partial_io);
-}
-
 /*
  * Reads (decompresses if needed) a page from zspool (zsmalloc).
  * Corresponding ZRAM slot should be locked.
@@ -1402,11 +1388,14 @@ static int zram_read_page(struct zram *zram, struct page *page, u32 index,
 		ret = zram_read_from_zspool(zram, page, index);
 		zram_slot_unlock(zram, index);
 	} else {
-		/* Slot should be unlocked before the function call */
+		/*
+		 * The slot should be unlocked before reading from the backing
+		 * device.
+		 */
 		zram_slot_unlock(zram, index);
 
-		ret = zram_bvec_read_from_bdev(zram, page, index, bio,
-					       partial_io);
+		ret = read_from_bdev(zram, page, zram_get_element(zram, index),
+				     bio, partial_io);
 	}
 
 	/* Should NEVER happen. Return bio error if it does. */