Re: [PATCH v2] virtio-balloon: Switch back to OOM handler for VIRTIO_BALLOON_F_DEFLATE_ON_OOM

David Hildenbrand
2020-03-10T11:20:52Z

On 10.03.20 12:19, Michael S. Tsirkin wrote:
> On Tue, Mar 10, 2020 at 12:12:50PM +0100, David Hildenbrand wrote:
>>>> 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.
>>
>>>
>>>> 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.

It's already really inconsistent, so I'll use vb->vdev in this patch and
cleanup the other users later.

--
Thanks,

David / dhildenb