Re: [QEMU Patch 2/2] virtio-balloon: support for handling page reporting

[Alexander Duyck <alexander.duyck@gmail.com>]

On Mon, Aug 12, 2019 at 6:14 AM Nitesh Narayan Lal <nitesh@redhat.com> wrote:
>
> Page reporting is a feature which enables the virtual machine to report
> chunk of free pages to the hypervisor.
> This patch enables QEMU to process these reports from the VM and discard the
> unused memory range.
>
> Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>
> ---
>  hw/virtio/virtio-balloon.c         | 41 ++++++++++++++++++++++++++++++
>  include/hw/virtio/virtio-balloon.h |  2 +-
>  2 files changed, 42 insertions(+), 1 deletion(-)
>
> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> index 25de154307..1132e47ee0 100644
> --- a/hw/virtio/virtio-balloon.c
> +++ b/hw/virtio/virtio-balloon.c
> @@ -320,6 +320,39 @@ static void balloon_stats_set_poll_interval(Object *obj, Visitor *v,
>      balloon_stats_change_timer(s, 0);
>  }
>
> +static void virtio_balloon_handle_reporting(VirtIODevice *vdev, VirtQueue *vq)
> +{
> +    VirtQueueElement *elem;
> +
> +    while ((elem = virtqueue_pop(vq, sizeof(VirtQueueElement)))) {
> +        unsigned int i;
> +
> +        for (i = 0; i < elem->in_num; i++) {
> +            void *gaddr = elem->in_sg[i].iov_base;
> +            size_t size = elem->in_sg[i].iov_len;
> +            ram_addr_t ram_offset;
> +            size_t rb_page_size;
> +           RAMBlock *rb;
> +
> +            if (qemu_balloon_is_inhibited())
> +                continue;
> +
> +            rb = qemu_ram_block_from_host(gaddr, false, &ram_offset);
> +            rb_page_size = qemu_ram_pagesize(rb);
> +
> +            /* For now we will simply ignore unaligned memory regions */
> +            if ((ram_offset | size) & (rb_page_size - 1))
> +                continue;
> +
> +            ram_block_discard_range(rb, ram_offset, size);
> +        }
> +
> +        virtqueue_push(vq, elem, 0);
> +        virtio_notify(vdev, vq);
> +        g_free(elem);
> +    }
> +}
> +

No offense, but I am a bit annoyed. If you are going to copy my code
you should at least keep up with the fixes. You are missing all of the
stuff to handle the poison value. If you are going to just duplicate
my setup you might as well have just pulled the QEMU patches from the
last submission I did. Then this would have at least has the fix for
the page poisoning. Also it wouldn't hurt to mention that you are
basing it off of the patch set I submitted since it hasn't been
accepted yet.

>  static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
>  {
>      VirtIOBalloon *s = VIRTIO_BALLOON(vdev);
> @@ -792,6 +825,12 @@ static void virtio_balloon_device_realize(DeviceState *dev, Error **errp)
>      s->dvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output);
>      s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats);
>
> +    if (virtio_has_feature(s->host_features,
> +                           VIRTIO_BALLOON_F_REPORTING)) {
> +        s->reporting_vq = virtio_add_queue(vdev, 16,
> +                                          virtio_balloon_handle_reporting);
> +    }
> +
>      if (virtio_has_feature(s->host_features,
>                             VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
>          s->free_page_vq = virtio_add_queue(vdev, VIRTQUEUE_MAX_SIZE,
> @@ -912,6 +951,8 @@ static Property virtio_balloon_properties[] = {
>       * is disabled, resulting in QEMU 3.1 migration incompatibility.  This
>       * property retains this quirk for QEMU 4.1 machine types.
>       */
> +    DEFINE_PROP_BIT("free-page-reporting", VirtIOBalloon, host_features,
> +                    VIRTIO_BALLOON_F_REPORTING, true),
>      DEFINE_PROP_BOOL("qemu-4-0-config-size", VirtIOBalloon,
>                       qemu_4_0_config_size, false),
>      DEFINE_PROP_LINK("iothread", VirtIOBalloon, iothread, TYPE_IOTHREAD,
> diff --git a/include/hw/virtio/virtio-balloon.h b/include/hw/virtio/virtio-balloon.h
> index d1c968d237..15a05e6435 100644
> --- a/include/hw/virtio/virtio-balloon.h
> +++ b/include/hw/virtio/virtio-balloon.h
> @@ -42,7 +42,7 @@ enum virtio_balloon_free_page_report_status {
>
>  typedef struct VirtIOBalloon {
>      VirtIODevice parent_obj;
> -    VirtQueue *ivq, *dvq, *svq, *free_page_vq;
> +    VirtQueue *ivq, *dvq, *svq, *free_page_vq, *reporting_vq;
>      uint32_t free_page_report_status;
>      uint32_t num_pages;
>      uint32_t actual;
> --
> 2.21.0
>q