Re: [PATCH v14 5/5] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_VQ

Michael S. Tsirkin
2017-08-18T02:13:17Z

On Thu, Aug 17, 2017 at 11:26:56AM +0800, Wei Wang wrote:
> Add a new vq to report hints of guest free pages to the host.

Please add some text here explaining the report_free_page_signal
thing.

I also really think we need some kind of ID in the
buffer to do a handshake. whenever id changes you
add another outbuf.

>
> Signed-off-by: Wei Wang <wei.w.wang@intel.com>
> Signed-off-by: Liang Li <liang.z.li@intel.com>
> ---
> drivers/virtio/virtio_balloon.c | 167 +++++++++++++++++++++++++++++++-----
> include/uapi/linux/virtio_balloon.h | 1 +
> 2 files changed, 147 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 72041b4..e6755bc 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -54,11 +54,12 @@ static struct vfsmount *balloon_mnt;
>
> struct virtio_balloon {
> struct virtio_device *vdev;
> - struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
> + struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *free_page_vq;
>
> /* The balloon servicing is delegated to a freezable workqueue. */
> struct work_struct update_balloon_stats_work;
> struct work_struct update_balloon_size_work;
> + struct work_struct report_free_page_work;
>
> /* Prevent updating balloon when it is being canceled. */
> spinlock_t stop_update_lock;
> @@ -90,6 +91,13 @@ struct virtio_balloon {
> /* Memory statistics */
> struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
>
> + /*
> + * Used by the device and driver to signal each other.
> + * device->driver: start the free page report.
> + * driver->device: end the free page report.
> + */
> + __virtio32 report_free_page_signal;

Weird - all I can see is driver writing 0 there, then adding
it as out buf.

> +
> /* To register callback in oom notifier call chain */
> struct notifier_block nb;
> };
> @@ -174,6 +182,17 @@ static void send_balloon_page_sg(struct virtio_balloon *vb,
> } while (unlikely(ret == -ENOSPC));
> }
>
> +static void send_free_page_sg(struct virtqueue *vq, void *addr, uint32_t size)
> +{
> + unsigned int len;
> +
> + add_one_sg(vq, addr, size);
> + virtqueue_kick(vq);
> + /* Release entries if there are */
> + while (virtqueue_get_buf(vq, &len))
> + ;
> +}
> +
> /*
> * Send balloon pages in sgs to host. The balloon pages are recorded in the
> * page xbitmap. Each bit in the bitmap corresponds to a page of PAGE_SIZE.
> @@ -511,42 +530,143 @@ static void update_balloon_size_func(struct work_struct *work)
> queue_work(system_freezable_wq, work);
> }
>
> +static void virtio_balloon_send_free_pages(void *opaque, unsigned long pfn,
> + unsigned long nr_pages)
> +{
> + struct virtio_balloon *vb = (struct virtio_balloon *)opaque;
> + void *addr = (void *)pfn_to_kaddr(pfn);
> + uint32_t len = nr_pages << PAGE_SHIFT;
> +
> + send_free_page_sg(vb->free_page_vq, addr, len);
> +}
> +
> +static void report_free_page_completion(struct virtio_balloon *vb)
> +{
> + struct virtqueue *vq = vb->free_page_vq;
> + struct scatterlist sg;
> + unsigned int len;
> + int ret;
> +
> + sg_init_one(&sg, &vb->report_free_page_signal, sizeof(__virtio32));

sizeof vb->report_free_page_signal is better.

> +retry:
> + ret = virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
> + virtqueue_kick(vq);
> + if (unlikely(ret == -ENOSPC)) {

what if there's another error?

> + wait_event(vb->acked, virtqueue_get_buf(vq, &len));
> + goto retry;
> + }

what is this trickery doing? needs more comments or
a simplification.

> +}
> +
> +static void report_free_page(struct work_struct *work)
> +{
> + struct virtio_balloon *vb;
> +
> + vb = container_of(work, struct virtio_balloon, report_free_page_work);
> + walk_free_mem_block(vb, 0, &virtio_balloon_send_free_pages);

That's a lot of work here. And system_wq documentation says:
*
* system_wq is the one used by schedule[_delayed]_work[_on]().
* Multi-CPU multi-threaded. There are users which expect relatively
* short queue flush time. Don't queue works which can run for too
* long.

You might want to create your own wq, maybe even with WQ_CPU_INTENSIVE.

> + report_free_page_completion(vb);

So first you get list of pages, then an outbuf telling you
what they are in end of. I think it's backwards.
Add an outbuf first followed by inbufs that tell you
what they are.

> +}
> +
> +static void free_page_request(struct virtqueue *vq)
> +{
> + struct virtio_balloon *vb = vq->vdev->priv;
> +
> + queue_work(system_freezable_wq, &vb->report_free_page_work);
> +}
> +
> static int init_vqs(struct virtio_balloon *vb)
> {
> - struct virtqueue *vqs[3];
> - vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
> - static const char * const names[] = { "inflate", "deflate", "stats" };
> - int err, nvqs;
> + struct virtqueue **vqs;
> + vq_callback_t **callbacks;
> + const char **names;
> + struct scatterlist sg;
> + int i, nvqs, err = -ENOMEM;
> +
> + /* Inflateq and deflateq are used unconditionally */
> + nvqs = 2;
> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ))
> + nvqs++;
> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_VQ))
> + nvqs++;
> +
> + /* Allocate space for find_vqs parameters */
> + vqs = kcalloc(nvqs, sizeof(*vqs), GFP_KERNEL);
> + if (!vqs)
> + goto err_vq;
> + callbacks = kmalloc_array(nvqs, sizeof(*callbacks), GFP_KERNEL);
> + if (!callbacks)
> + goto err_callback;
> + names = kmalloc_array(nvqs, sizeof(*names), GFP_KERNEL);
> + if (!names)
> + goto err_names;
> +
> + callbacks[0] = balloon_ack;
> + names[0] = "inflate";
> + callbacks[1] = balloon_ack;
> + names[1] = "deflate";
> +
> + i = 2;
> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
> + callbacks[i] = stats_request;
> + names[i] = "stats";
> + i++;
> + }
>
> - /*
> - * We expect two virtqueues: inflate and deflate, and
> - * optionally stat.
> - */
> - nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
> - err = virtio_find_vqs(vb->vdev, nvqs, vqs, callbacks, names, NULL);
> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_VQ)) {
> + callbacks[i] = free_page_request;
> + names[i] = "free_page_vq";
> + }
> +
> + err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks, names,
> + NULL, NULL);
> if (err)
> - return err;
> + goto err_find;
>
> vb->inflate_vq = vqs[0];
> vb->deflate_vq = vqs[1];
> + i = 2;
> if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
> - struct scatterlist sg;
> - unsigned int num_stats;
> - vb->stats_vq = vqs[2];
> -
> + vb->stats_vq = vqs[i++];
> /*
> * Prime this virtqueue with one buffer so the hypervisor can
> * use it to signal us later (it can't be broken yet!).
> */
> - num_stats = update_balloon_stats(vb);
> -
> - sg_init_one(&sg, vb->stats, sizeof(vb->stats[0]) * num_stats);
> + sg_init_one(&sg, vb->stats, sizeof(vb->stats));
> if (virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb, GFP_KERNEL)
> - < 0)
> - BUG();
> + < 0) {
> + dev_warn(&vb->vdev->dev, "%s: add stat_vq failed\n",
> + __func__);
> + goto err_find;
> + }
> virtqueue_kick(vb->stats_vq);
> }
> +
> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_VQ)) {
> + vb->free_page_vq = vqs[i];
> + vb->report_free_page_signal = 0;
> + sg_init_one(&sg, &vb->report_free_page_signal,
> + sizeof(__virtio32));
> + if (virtqueue_add_outbuf(vb->free_page_vq, &sg, 1, vb,
> + GFP_KERNEL) < 0) {
> + dev_warn(&vb->vdev->dev, "%s: add signal buf failed\n",
> + __func__);
> + goto err_find;
> + }
> + virtqueue_kick(vb->free_page_vq);
> + }
> +
> + kfree(names);
> + kfree(callbacks);
> + kfree(vqs);
> return 0;
> +
> +err_find:
> + kfree(names);
> +err_names:
> + kfree(callbacks);
> +err_callback:
> + kfree(vqs);
> +err_vq:
> + return err;
> }
>
> #ifdef CONFIG_BALLOON_COMPACTION
> @@ -675,6 +795,9 @@ static int virtballoon_probe(struct virtio_device *vdev)
> if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_SG))
> xb_init(&vb->page_xb);
>
> + if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_VQ))
> + INIT_WORK(&vb->report_free_page_work, report_free_page);
> +
> vb->nb.notifier_call = virtballoon_oom_notify;
> vb->nb.priority = VIRTBALLOON_OOM_NOTIFY_PRIORITY;
> err = register_oom_notifier(&vb->nb);
> @@ -739,6 +862,7 @@ static void virtballoon_remove(struct virtio_device *vdev)
> spin_unlock_irq(&vb->stop_update_lock);
> cancel_work_sync(&vb->update_balloon_size_work);
> cancel_work_sync(&vb->update_balloon_stats_work);
> + cancel_work_sync(&vb->report_free_page_work);
>
> remove_common(vb);
> #ifdef CONFIG_BALLOON_COMPACTION
> @@ -792,6 +916,7 @@ static unsigned int features[] = {
> VIRTIO_BALLOON_F_STATS_VQ,
> VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
> VIRTIO_BALLOON_F_SG,
> + VIRTIO_BALLOON_F_FREE_PAGE_VQ,
> };
>
> static struct virtio_driver virtio_balloon_driver = {
> diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
> index 37780a7..8214f84 100644
> --- a/include/uapi/linux/virtio_balloon.h
> +++ b/include/uapi/linux/virtio_balloon.h
> @@ -35,6 +35,7 @@
> #define VIRTIO_BALLOON_F_STATS_VQ 1 /* Memory Stats virtqueue */
> #define VIRTIO_BALLOON_F_DEFLATE_ON_OOM 2 /* Deflate balloon on OOM */
> #define VIRTIO_BALLOON_F_SG 3 /* Use sg instead of PFN lists */
> +#define VIRTIO_BALLOON_F_FREE_PAGE_VQ 4 /* Virtqueue to report free pages */
>
> /* Size of a PFN in the balloon interface. */
> #define VIRTIO_BALLOON_PFN_SHIFT 12
> --
> 2.7.4