linux-kernel - Re: [RFC 1/2] virtio_balloon: move balloon

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Date:	Fri, 10 May 2013 08:52:26 -0400
From:	Luiz Capitulino <lcapitulino@...hat.com>
To:	Rafael Aquini <aquini@...hat.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, riel@...hat.com, mst@...hat.com,
	amit.shah@...hat.com, anton@...msg.org
Subject: Re: [RFC 1/2] virtio_balloon: move balloon_lock mutex to callers

On Thu, 9 May 2013 18:03:09 -0300
Rafael Aquini <aquini@...hat.com> wrote:

> On Thu, May 09, 2013 at 10:53:48AM -0400, Luiz Capitulino wrote:
> > This commit moves the balloon_lock mutex out of the fill_balloon()
> > and leak_balloon() functions to their callers.
> > 
> > The reason for this change is that the next commit will introduce
> > a shrinker callback for the balloon driver, which will also call
> > leak_balloon() but will require different locking semantics.
> > 
> > Signed-off-by: Luiz Capitulino <lcapitulino@...hat.com>
> > ---
> >  drivers/virtio/virtio_balloon.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> > index bd3ae32..9d5fe2b 100644
> > --- a/drivers/virtio/virtio_balloon.c
> > +++ b/drivers/virtio/virtio_balloon.c
> > @@ -133,7 +133,6 @@ static void fill_balloon(struct virtio_balloon *vb, size_t num)
> >  	/* We can only do one array worth at a time. */
> >  	num = min(num, ARRAY_SIZE(vb->pfns));
> >  
> > -	mutex_lock(&vb->balloon_lock);
> >  	for (vb->num_pfns = 0; vb->num_pfns < num;
> >  	     vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
> >  		struct page *page = balloon_page_enqueue(vb_dev_info);
> > @@ -154,7 +153,6 @@ static void fill_balloon(struct virtio_balloon *vb, size_t num)
> >  	/* Did we get any? */
> >  	if (vb->num_pfns != 0)
> >  		tell_host(vb, vb->inflate_vq);
> > -	mutex_unlock(&vb->balloon_lock);
> >  }
> >  
> >  static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
> > @@ -176,7 +174,6 @@ static void leak_balloon(struct virtio_balloon *vb, size_t num)
> >  	/* We can only do one array worth at a time. */
> >  	num = min(num, ARRAY_SIZE(vb->pfns));
> >  
> > -	mutex_lock(&vb->balloon_lock);
> >  	for (vb->num_pfns = 0; vb->num_pfns < num;
> >  	     vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
> >  		page = balloon_page_dequeue(vb_dev_info);
> > @@ -192,7 +189,6 @@ static void leak_balloon(struct virtio_balloon *vb, size_t num)
> >  	 * is true, we *have* to do it in this order
> >  	 */
> >  	tell_host(vb, vb->deflate_vq);
> > -	mutex_unlock(&vb->balloon_lock);
> >  	release_pages_by_pfn(vb->pfns, vb->num_pfns);
> >  }
> >  
> > @@ -305,11 +301,13 @@ static int balloon(void *_vballoon)
> >  					 || freezing(current));
> >  		if (vb->need_stats_update)
> >  			stats_handle_request(vb);
> > +		mutex_lock(&vb->balloon_lock);
> >  		if (diff > 0)
> >  			fill_balloon(vb, diff);
> >  		else if (diff < 0)
> >  			leak_balloon(vb, -diff);
> >  		update_balloon_size(vb);
> > +		mutex_unlock(&vb->balloon_lock);
> >  	}
> >  	return 0;
> >  }
> > @@ -490,9 +488,11 @@ out:
> >  static void remove_common(struct virtio_balloon *vb)
> >  {
> >  	/* There might be pages left in the balloon: free them. */
> > +	mutex_lock(&vb->balloon_lock);
> >  	while (vb->num_pages)
> >  		leak_balloon(vb, vb->num_pages);
> >  	update_balloon_size(vb);
> > +	mutex_unlock(&vb->balloon_lock);
> 
> I think you will need to introduce the same change as above to virtballoon_restore()

Thanks Rafael, I've fixed it in my tree.
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