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

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Date:	Thu, 9 May 2013 18:03:09 -0300
From:	Rafael Aquini <aquini@...hat.com>
To:	Luiz Capitulino <lcapitulino@...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, 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()


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