ext4: pass write-hint for buffered IO

Commit 4498135 ("block, fs: Restore the per-bio/request data
lifetime fields") restored write-hint support in ext4. But that is
applicable only for direct IO. This patch supports passing
write-hint for buffered IO from ext4 file system to block layer
by filling bi_write_hint of struct bio in io_submit_add_bh().

Signed-off-by: j.xia <j.xia@samsung.com>
Link: https://patch.msgid.link/20240919020341.2657646-1-j.xia@samsung.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Author: tracy2015

fs/ext4/page-io.c

@@ -417,8 +417,10 @@ static void io_submit_add_bh(struct ext4_io_submit *io,
 submit_and_retry:
 		ext4_io_submit(io);
 	}
-	if (io->io_bio == NULL)
+	if (io->io_bio == NULL) {
 		io_submit_init_bio(io, bh);
+		io->io_bio->bi_write_hint = inode->i_write_hint;
+	}
 	if (!bio_add_folio(io->io_bio, io_folio, bh->b_size, bh_offset(bh)))
 		goto submit_and_retry;
 	wbc_account_cgroup_owner(io->io_wbc, &folio->page, bh->b_size);