Re: [PATCH v24 2/2] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

[Wei Wang <wei.w.wang@intel.com>]

On 01/25/2018 01:15 AM, Michael S. Tsirkin wrote:
> On Wed, Jan 24, 2018 at 06:42:42PM +0800, Wei Wang wrote:
> +
> +static void report_free_page_func(struct work_struct *work)
> +{
> +	struct virtio_balloon *vb;
> +	unsigned long flags;
> +
> +	vb = container_of(work, struct virtio_balloon, report_free_page_work);
> +
> +	/* Start by sending the obtained cmd id to the host with an outbuf */
> +	send_cmd_id(vb, &vb->start_cmd_id);
> +
> +	/*
> +	 * Set start_cmd_id to VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID to
> +	 * indicate a new request can be queued.
> +	 */
> +	spin_lock_irqsave(&vb->stop_update_lock, flags);
> +	vb->start_cmd_id = cpu_to_virtio32(vb->vdev,
> +				VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID);
> +	spin_unlock_irqrestore(&vb->stop_update_lock, flags);
> +
> +	walk_free_mem_block(vb, 0, &virtio_balloon_send_free_pages);
> Can you teach walk_free_mem_block to return the && of all
> return calls, so caller knows whether it completed?

There will be two cases that can cause walk_free_mem_block to return 
without completing:
1) host requests to stop in advance
2) vq->broken

How about letting walk_free_mem_block simply return the value returned 
by its callback (i.e. virtio_balloon_send_free_pages)?

For host requests to stop, it returns "1", and the above only bails out 
when walk_free_mem_block return a "< 0" value.

Best,
Wei