linux-kernel - Re: [PATCH RFC] virtio_balloon: refill by config handler

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Date:	Tue, 5 Jan 2016 17:31:36 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Petr Mladek <pmladek@...e.com>
Cc:	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Jeff Epler <jepler@...ythonic.net>, Tejun Heo <tj@...nel.org>,
	Jiri Kosina <jkosina@...e.cz>
Subject: Re: [PATCH RFC] virtio_balloon: refill by config handler

On Tue, Jan 05, 2016 at 03:37:33PM +0100, Petr Mladek wrote:
> On Fri 2016-01-01 12:13:48, Michael S. Tsirkin wrote:
> > Peter Mladek reported that balloon might never refill completely after
> > restore.  This is because fill_balloon is only called once there.
> > Calling fill_balloon repeatedly seems too aggressive,
> > especially in light of the fact that it sleeps on failure: let's
> > wake the config change handler and fill it asynchronously.
> > 
> > Reported-by: Petr Mladek <pmladek@...e.com>
> > Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> > ---
> > 
> > I was unable to test this - for some reason my test VM
> > doesn't resume (with or without the patch).
> > Petr, does this work for you?
> 
> Ah, I have just realized that the problem happens only after the
> conversion to the workqueue. It works without this patch with the
> current code. The balloon kthread is waken when released from
> __refrigerator().

In fact, maybe we should drop fill_balloon and
update_balloon_size here?
Resume will finish faster ...

> I am sorry for the noise. I wanted to split the conversion to
> workqueues into two patches to make it better readable. We need to
> queue the balloon resizing work here. I wrongly assumed that the
> original kthread must have the same problem.
> 
> Best Regards,
> Petr
> 
> >  drivers/virtio/virtio_balloon.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> > index 7efc329..ee29473 100644
> > --- a/drivers/virtio/virtio_balloon.c
> > +++ b/drivers/virtio/virtio_balloon.c
> > @@ -589,7 +589,7 @@ static int virtballoon_restore(struct virtio_device *vdev)
> >  
> >  	virtio_device_ready(vdev);
> >  
> > -	fill_balloon(vb, towards_target(vb));
> > +	wake_up(&vb->config_change);
> >  	update_balloon_size(vb);
> >  	return 0;
> >  }
> > -- 
> > MST
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