zram: refactor zram_bdev_write

Split the read/modify/write case into a separate helper.

Link: https://lkml.kernel.org/r/20230411171459.567614-14-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

drivers/block/zram/zram_drv.c

@@ -1568,33 +1568,33 @@ static int zram_write_page(struct zram *zram, struct page *page, u32 index)
 	return ret;
 }
 
-static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
-				u32 index, int offset, struct bio *bio)
+/*
+ * This is a partial IO. Read the full page before writing the changes.
+ */
+static int zram_bvec_write_partial(struct zram *zram, struct bio_vec *bvec,
+				   u32 index, int offset, struct bio *bio)
 {
-	struct page *page = bvec->bv_page;
+	struct page *page = alloc_page(GFP_NOIO);
 	int ret;
 
-	if (is_partial_io(bvec)) {
-		/*
-		 * This is a partial IO. We need to read the full page
-		 * before to write the changes.
-		 */
-		page = alloc_page(GFP_NOIO);
-		if (!page)
-			return -ENOMEM;
-
-		ret = zram_read_page(zram, page, index, bio, true);
-		if (ret)
-			goto out;
+	if (!page)
+		return -ENOMEM;
 
+	ret = zram_read_page(zram, page, index, bio, true);
+	if (!ret) {
 		memcpy_from_bvec(page_address(page) + offset, bvec);
+		ret = zram_write_page(zram, page, index);
 	}
+	__free_page(page);
+	return ret;
+}
 
-	ret = zram_write_page(zram, page, index);
-out:
+static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
+			   u32 index, int offset, struct bio *bio)
+{
 	if (is_partial_io(bvec))
-		__free_page(page);
-	return ret;
+		return zram_bvec_write_partial(zram, bvec, index, offset, bio);
+	return zram_write_page(zram, bvec->bv_page, index);
 }
 
 #ifdef CONFIG_ZRAM_MULTI_COMP