bcache: print written and keys in trace_bcache_btree_write

It's useful to dump written block and keys on btree write, this patch
add them into trace_bcache_btree_write.

Signed-off-by: Guoju Fang <fangguoju@gmail.com>
Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/trace/events/bcache.h

@@ -275,7 +275,8 @@ TRACE_EVENT(bcache_btree_write,
 		__entry->keys	= b->keys.set[b->keys.nsets].data->keys;
 	),
 
-	TP_printk("bucket %zu", __entry->bucket)
+	TP_printk("bucket %zu written block %u + %u",
+		__entry->bucket, __entry->block, __entry->keys)
 );
 
 DEFINE_EVENT(btree_node, bcache_btree_node_alloc,