btrfs: add support for passing in write hints for buffered writes

Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Chris Mason <clm@fb.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/btrfs/extent_io.c

@@ -2830,6 +2830,7 @@ static int submit_extent_page(int op, int op_flags, struct extent_io_tree *tree,
 	bio_add_page(bio, page, page_size, offset);
 	bio->bi_end_io = end_io_func;
 	bio->bi_private = tree;
+	bio->bi_write_hint = page->mapping->host->i_write_hint;
 	bio_set_op_attrs(bio, op, op_flags);
 	if (wbc) {
 		wbc_init_bio(wbc, bio);