Re: [Qemu-devel] [PATCH v7 4/5] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

[Wei Wang]

On 05/29/2018 11:24 PM, Michael S. Tsirkin wrote:
> On Tue, Apr 24, 2018 at 02:13:47PM +0800, Wei Wang wrote:
> > +/*
> > + * Balloon will report pages which were free at the time of this call. As the
> > + * reporting happens asynchronously, dirty bit logging must be enabled before
> > + * this call is made.
> > + */
> > +void balloon_free_page_start(void)
> > +{
> > +    balloon_free_page_start_fn(balloon_opaque);
> > +}
> Please create notifier support, not a single global.

OK. The start is called at the end of bitmap_sync, and the stop is 
called at the beginning of bitmap_sync. In this case, we will need to 
add two migration states, MIGRATION_STATUS_BEFORE_BITMAP_SYNC and 
MIGRATION_STATUS_AFTER_BITMAP_SYNC, right?


> +static void virtio_balloon_poll_free_page_hints(void *opaque)
> +{
> +    VirtQueueElement *elem;
> +    VirtIOBalloon *dev = opaque;
> +    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> +    VirtQueue *vq = dev->free_page_vq;
> +    uint32_t id;
> +    size_t size;
> +
> +    while (1) {
> +        qemu_mutex_lock(&dev->free_page_lock);
> +        while (dev->block_iothread) {
> +            qemu_cond_wait(&dev->free_page_cond, &dev->free_page_lock);
> +        }
> +
> +        /*
> +         * If the migration thread actively stops the reporting, exit
> +         * immediately.
> +         */
> +        if (dev->free_page_report_status == FREE_PAGE_REPORT_S_STOP) {
> Please refactor this : move loop body into a function so
> you can do lock/unlock in a single place.

Sounds good.

> +
> +static bool virtio_balloon_free_page_support(void *opaque)
> +{
> +    VirtIOBalloon *s = opaque;
> +    VirtIODevice *vdev = VIRTIO_DEVICE(s);
> +
> +    return virtio_vdev_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT);
> or if poison is negotiated.

Will make it
return virtio_vdev_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT) && 
!virtio_vdev_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)


Best,
Wei