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

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, May 30, 2018 at 05:12:09PM +0800, Wei Wang wrote:
> 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?

If that's the way you do it, you need to ask migration guys, not me.

> 
> > 
> > +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)


I mean the reverse:
	virtio_vdev_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT) ||
	virtio_vdev_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)


If poison has been negotiated you must migrate the
guest supplied value even if you don't use it for hints.


> 
> 
> Best,
> Wei