f2fs: move bio_private allocation out of f2fs_bio_alloc()

bio->bi_private is not always needed. As in the reading data path,
end_read_io does not need bio_private for further using, so moving
bio_private allocation out of f2fs_bio_alloc(). Alloc it in the
submit_write_page(), and ignore it in the f2fs_readpage().
Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/data.c

@@ -365,7 +365,6 @@ static void read_end_io(struct bio *bio, int err)
 		}
 		unlock_page(page);
 	} while (bvec >= bio->bi_io_vec);
-	kfree(bio->bi_private);
 	bio_put(bio);
 }
 

fs/f2fs/segment.c

@@ -611,18 +611,12 @@ static void f2fs_end_io_write(struct bio *bio, int err)
 struct bio *f2fs_bio_alloc(struct block_device *bdev, int npages)
 {
 	struct bio *bio;
-	struct bio_private *priv;
-retry:
-	priv = kmalloc(sizeof(struct bio_private), GFP_NOFS);
-	if (!priv) {
-		cond_resched();
-		goto retry;
-	}
 
 	/* No failure on bio allocation */
 	bio = bio_alloc(GFP_NOIO, npages);
 	bio->bi_bdev = bdev;
-	bio->bi_private = priv;
+	bio->bi_private = NULL;
+
 	return bio;
 }
 
@@ -681,8 +675,17 @@ static void submit_write_page(struct f2fs_sb_info *sbi, struct page *page,
 		do_submit_bio(sbi, type, false);
 alloc_new:
 	if (sbi->bio[type] == NULL) {
+		struct bio_private *priv;
+retry:
+		priv = kmalloc(sizeof(struct bio_private), GFP_NOFS);
+		if (!priv) {
+			cond_resched();
+			goto retry;
+		}
+
 		sbi->bio[type] = f2fs_bio_alloc(bdev, max_hw_blocks(sbi));
 		sbi->bio[type]->bi_sector = SECTOR_FROM_BLOCK(sbi, blk_addr);
+		sbi->bio[type]->bi_private = priv;
 		/*
 		 * The end_io will be assigned at the sumbission phase.
 		 * Until then, let bio_add_page() merge consecutive IOs as much