On Tue, Mar 10, 2020 at 12:12:50PM +0100, David Hildenbrand wrote:

quoted

quoted

 static void virtio_balloon_unregister_shrinker(struct virtio_balloon *vb)

@@ -971,7 +950,22 @@ static int virtballoon_probe(struct virtio_device *vdev)
 						  VIRTIO_BALLOON_CMD_ID_STOP);
 		spin_lock_init(&vb->free_page_list_lock);
 		INIT_LIST_HEAD(&vb->free_page_list);
+		/*
+		 * We're allowed to reuse any free pages, even if they are
+		 * still to be processed by the host.
+		 */
+		err = virtio_balloon_register_shrinker(vb);
+		if (err)
+			goto out_del_balloon_wq;
 	}
+	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) {
+		vb->oom_nb.notifier_call = virtio_balloon_oom_notify;
+		vb->oom_nb.priority = VIRTIO_BALLOON_OOM_NOTIFY_PRIORITY;
+		err = register_oom_notifier(&vb->oom_nb);
+		if (err < 0)
+			goto out_unregister_shrinker;
+	}
+

Let's decide whether we want an empty line after }, or not, and stick to
it. I prefer an empty line but no biggie as long as we are consistent.

Can add one.

quoted

quoted

 	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) {
 		/* Start with poison val of 0 representing general init */
 		__u32 poison_val = 0;

@@ -986,15 +980,6 @@ static int virtballoon_probe(struct virtio_device *vdev)
 		virtio_cwrite(vb->vdev, struct virtio_balloon_config,
 			      poison_val, &poison_val);
 	}
-	/*
-	 * We continue to use VIRTIO_BALLOON_F_DEFLATE_ON_OOM to decide if a
-	 * shrinker needs to be registered to relieve memory pressure.
-	 */
-	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) {
-		err = virtio_balloon_register_shrinker(vb);
-		if (err)
-			goto out_del_balloon_wq;
-	}
 
 	vb->pr_dev_info.report = virtballoon_free_page_report;
 	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) {

@@ -1003,12 +988,12 @@ static int virtballoon_probe(struct virtio_device *vdev)
 		capacity = virtqueue_get_vring_size(vb->reporting_vq);
 		if (capacity < PAGE_REPORTING_CAPACITY) {
 			err = -ENOSPC;
-			goto out_unregister_shrinker;
+			goto out_unregister_oom;
 		}
 
 		err = page_reporting_register(&vb->pr_dev_info);
 		if (err)
-			goto out_unregister_shrinker;
+			goto out_unregister_oom;
 	}
 
 	virtio_device_ready(vdev);

@@ -1017,8 +1002,11 @@ static int virtballoon_probe(struct virtio_device *vdev)
 		virtballoon_changed(vdev);
 	return 0;
 
+out_unregister_oom:
+	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
+		unregister_oom_notifier(&vb->oom_nb);
 out_unregister_shrinker:
-	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
+	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
 		virtio_balloon_unregister_shrinker(vb);

What's with vdev versus vb->vdev here?
I suggest we keep using vb->vdev to make the patch minimal if we can.
Same elsewhere.

As we touch this line either way, does it really make a difference? No
strong opinion. Can just do a vb->vdev and clean this up globally later.

Let's just be consistent. I guess that means keep using vb->vdev
everywhere.

-- 
Thanks,

David / dhildenb