[PATCH 3/3] virtio_balloon: add tracepoints for free page hinting and migration

@@ -803,6 +803,7 @@ static void virtio_balloon_report_free_page(struct virtio_balloon *vb)
 {
 	int err;
 	struct device *dev = &vb->vdev->dev;
+	unsigned int cmd_id = virtio_balloon_cmd_id_received(vb);
 
 	/* Start by sending the received cmd id to host with an outbuf. */
 	err = send_cmd_id_start(vb);

@@ -817,6 +818,9 @@ static void virtio_balloon_report_free_page(struct virtio_balloon *vb)
 	err = send_cmd_id_stop(vb);
 	if (unlikely(err))
 		dev_err(dev, "Failed to send a stop id, err = %d\n", err);
+
+	trace_virtio_balloon_free_page_hint(cmd_id,
+					    READ_ONCE(vb->num_free_page_blocks));
 }
 
 static void report_free_page_func(struct work_struct *work)

@@ -869,8 +873,11 @@ static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
 	 * recursion in the case it ends up triggering memory compaction
 	 * while it is attempting to inflate the ballon.
 	 */
-	if (!mutex_trylock(&vb->balloon_lock))
+	if (!mutex_trylock(&vb->balloon_lock)) {
+		trace_virtio_balloon_migrate(page_to_pfn(page),
+					     page_to_pfn(newpage), -EAGAIN);
 		return -EAGAIN;
+	}
 
 	/* balloon's page migration 1st step  -- inflate "newpage" */
 	vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;

@@ -883,6 +890,8 @@ static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
 	tell_host(vb, vb->deflate_vq);
 
 	mutex_unlock(&vb->balloon_lock);
+
+	trace_virtio_balloon_migrate(page_to_pfn(page), page_to_pfn(newpage), 0);
 	return 0;
 }
 #endif /* CONFIG_BALLOON_MIGRATION */

@@ -103,6 +103,54 @@ TRACE_EVENT(virtio_balloon_host_ack,
 		  __get_str(vq_name), __entry->num_pfns, __entry->latency_ns)
 );
 
+TRACE_EVENT(virtio_balloon_free_page_hint,
+
+	/*
+	 * outstanding_blocks is the number of hint blocks still owned by the
+	 * balloon (handed to the host but not yet reclaimed via a DONE/STOP
+	 * command) at the end of the reporting round.  A high value means the
+	 * host did not fully drain the round.
+	 */
+	TP_PROTO(u32 cmd_id, unsigned long outstanding_blocks),
+
+	TP_ARGS(cmd_id, outstanding_blocks),
+
+	TP_STRUCT__entry(
+		__field(u32, cmd_id)
+		__field(unsigned long, outstanding_blocks)
+	),
+
+	TP_fast_assign(
+		__entry->cmd_id = cmd_id;
+		__entry->outstanding_blocks = outstanding_blocks;
+	),
+
+	TP_printk("cmd_id=%u outstanding_blocks=%lu",
+		  __entry->cmd_id, __entry->outstanding_blocks)
+);
+
+TRACE_EVENT(virtio_balloon_migrate,
+
+	TP_PROTO(unsigned long old_pfn, unsigned long new_pfn, long ret),
+
+	TP_ARGS(old_pfn, new_pfn, ret),
+
+	TP_STRUCT__entry(
+		__field(unsigned long, old_pfn)
+		__field(unsigned long, new_pfn)
+		__field(long, ret)
+	),
+
+	TP_fast_assign(
+		__entry->old_pfn = old_pfn;
+		__entry->new_pfn = new_pfn;
+		__entry->ret = ret;
+	),
+
+	TP_printk("old_pfn=0x%lx new_pfn=0x%lx ret=%ld",
+		  __entry->old_pfn, __entry->new_pfn, __entry->ret)
+);
+
 #endif /* _TRACE_VIRTIO_BALLOON_H */
 
 /* This part must be outside protection */