linux-kernel - Re: [PATCH v2] virtio-balloon: Switch back to OOM handler for VIRTIO_BALLOON_F_DEFLATE_ON

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Date:   Tue, 10 Mar 2020 07:19:13 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        virtualization@...ts.linux-foundation.org,
        Jason Wang <jasowang@...hat.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Tyler Sanderson <tysand@...gle.com>,
        Wei Wang <wei.w.wang@...el.com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Nadav Amit <namit@...are.com>,
        Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2] virtio-balloon: Switch back to OOM handler for
 VIRTIO_BALLOON_F_DEFLATE_ON_OOM

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.

> -- 
> Thanks,
> 
> David / dhildenb