btrfs: zoned: don't clear dirty flag of extent buffer

One a zoned filesystem, never clear the dirty flag of an extent buffer,
but instead mark it as zeroout.

On writeout, when encountering a marked extent_buffer, zero it out.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/disk-io.c

@@ -254,8 +254,13 @@ blk_status_t btree_csum_one_bio(struct btrfs_bio *bbio)
 	if (WARN_ON_ONCE(bbio->bio.bi_iter.bi_size != eb->len))
 		return BLK_STS_IOERR;
 
+	/*
+	 * If an extent_buffer is marked as EXTENT_BUFFER_ZONED_ZEROOUT, don't
+	 * checksum it but zero-out its content. This is done to preserve
+	 * ordering of I/O without unnecessarily writing out data.
+	 */
 	if (test_bit(EXTENT_BUFFER_ZONED_ZEROOUT, &eb->bflags)) {
-		WARN_ON_ONCE(found_start != 0);
+		memzero_extent_buffer(eb, 0, eb->len);
 		return BLK_STS_OK;
 	}
 

fs/btrfs/extent_io.c

@@ -3761,6 +3761,20 @@ void btrfs_clear_buffer_dirty(struct btrfs_trans_handle *trans,
 	if (trans && btrfs_header_generation(eb) != trans->transid)
 		return;
 
+	/*
+	 * Instead of clearing the dirty flag off of the buffer, mark it as
+	 * EXTENT_BUFFER_ZONED_ZEROOUT. This allows us to preserve
+	 * write-ordering in zoned mode, without the need to later re-dirty
+	 * the extent_buffer.
+	 *
+	 * The actual zeroout of the buffer will happen later in
+	 * btree_csum_one_bio.
+	 */
+	if (btrfs_is_zoned(fs_info)) {
+		set_bit(EXTENT_BUFFER_ZONED_ZEROOUT, &eb->bflags);
+		return;
+	}
+
 	if (!test_and_clear_bit(EXTENT_BUFFER_DIRTY, &eb->bflags))
 		return;
 
@@ -4152,8 +4166,6 @@ static void __write_extent_buffer(const struct extent_buffer *eb,
 	/* For unmapped (dummy) ebs, no need to check their uptodate status. */
 	const bool check_uptodate = !test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags);
 
-	WARN_ON(test_bit(EXTENT_BUFFER_ZONED_ZEROOUT, &eb->bflags));
-
 	if (check_eb_range(eb, start, len))
 		return;
 

fs/btrfs/zoned.c

@@ -1713,7 +1713,8 @@ void btrfs_redirty_list_add(struct btrfs_transaction *trans,
 	    btrfs_header_flag(eb, BTRFS_HEADER_FLAG_WRITTEN))
 		return;
 
-	ASSERT(!test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
+	ASSERT(test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
+	ASSERT(test_bit(EXTENT_BUFFER_ZONED_ZEROOUT, &eb->bflags));
 
 	memzero_extent_buffer(eb, 0, eb->len);
 	set_bit(EXTENT_BUFFER_ZONED_ZEROOUT, &eb->bflags);