Re: [virtio-dev] Re: [PATCH v4 3/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

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

On 03/14/2018 12:49 AM, Michael S. Tsirkin wrote:
> On Wed, Mar 07, 2018 at 08:34:24PM +0800, Wei Wang wrote:
>
> > Signed-off-by: Wei Wang <wei.w.wang@intel.com>
> > Signed-off-by: Liang Li <liang.z.li@intel.com>
> > CC: Michael S. Tsirkin <mst@redhat.com>
> > CC: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > CC: Juan Quintela <quintela@redhat.com>
> I find it suspicious that neither unrealize nor reset
> functions have been touched at all.
> Are you sure you have thought through scenarious like
> hot-unplug or disabling the device by guest?
>    

OK. I think we can call balloon_free_page_stop in unrealize and reset.


>   
> +static void *virtio_balloon_poll_free_page_hints(void *opaque)
> +{
> +    VirtQueueElement *elem;
> +    VirtIOBalloon *dev = opaque;
> +    VirtQueue *vq = dev->free_page_vq;
> +    uint32_t id;
> +    size_t size;
> What makes it safe to poke at this device from multiple threads?
> I think that it would be safer to do it from e.g. BH.

Actually the free_page_optimization thread is the only user of 
free_page_vq, and there is only one optimization thread each time. Would 
this be safe enough?

Best,
Wei