Re: [PATCH v13 5/5] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_VQ

[Pankaj Gupta]

> 
> Add a new vq to report hints of guest free pages to the host.
> 
> Signed-off-by: Wei Wang <wei.w.wang@xxxxxxxxx>
> Signed-off-by: Liang Li <liang.z.li@xxxxxxxxx>
> ---
>  drivers/virtio/virtio_balloon.c     | 164
>  ++++++++++++++++++++++++++++++------
>  include/uapi/linux/virtio_balloon.h |   1 +
>  2 files changed, 140 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c
> b/drivers/virtio/virtio_balloon.c
> index 29aca0c..29c4a61 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;
> +
>          /* To register callback in oom notifier call chain */
>          struct notifier_block nb;
>  };
> @@ -146,7 +154,7 @@ static void set_page_pfns(struct virtio_balloon *vb,
>  }
>  
>  static void send_one_sg(struct virtio_balloon *vb, struct virtqueue *vq,
> -                        void *addr, uint32_t size)
> +                        void *addr, uint32_t size, bool busywait)
>  {
>          struct scatterlist sg;
>          unsigned int len;
> @@ -165,7 +173,12 @@ static void send_one_sg(struct virtio_balloon *vb,
> struct virtqueue *vq,
>                          cpu_relax();
>          }
>          virtqueue_kick(vq);
> -        wait_event(vb->acked, virtqueue_get_buf(vq, &len));
> +        if (busywait)
> +                while (!virtqueue_get_buf(vq, &len) &&
> +                       !virtqueue_is_broken(vq))
> +                        cpu_relax();
> +        else
> +                wait_event(vb->acked, virtqueue_get_buf(vq, &len));
>  }
>  
>  /*
> @@ -197,11 +210,11 @@ static void tell_host_sgs(struct virtio_balloon *vb,
>                  sg_addr = pfn_to_kaddr(sg_pfn_start);
>                  sg_len = (sg_pfn_end - sg_pfn_start) << PAGE_SHIFT;
>                  while (sg_len > sg_max_len) {
> -                        send_one_sg(vb, vq, sg_addr, sg_max_len);
> +                        send_one_sg(vb, vq, sg_addr, sg_max_len, 0);
>                          sg_addr += sg_max_len;
>                          sg_len -= sg_max_len;
>                  }
> -                send_one_sg(vb, vq, sg_addr, sg_len);
> +                send_one_sg(vb, vq, sg_addr, sg_len, 0);
>                  xb_zero(&vb->page_xb, sg_pfn_start, sg_pfn_end);
>                  sg_pfn_start = sg_pfn_end + 1;
>          }
> @@ -503,42 +516,138 @@ 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 = pfn_to_kaddr(pfn);
> +        uint32_t len = nr_pages << PAGE_SHIFT;
> +
> +        send_one_sg(vb, vb->free_page_vq, addr, len, 1);
> +}
> +
> +static void report_free_page_completion(struct virtio_balloon *vb)
> +{
> +        struct virtqueue *vq = vb->free_page_vq;
> +        struct scatterlist sg;
> +        unsigned int len;
> +
> +        sg_init_one(&sg, &vb->report_free_page_signal, sizeof(__virtio32));
> +        while (unlikely(virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL)
> +                        == -ENOSPC)) {
> +                virtqueue_kick(vq);
> +                while (!virtqueue_get_buf(vq, &len) &&
> +                       !virtqueue_is_broken(vq))
> +                        cpu_relax();
> +        }
> +        virtqueue_kick(vq);
> +}
> +
> +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, 1, &virtio_balloon_send_free_pages);
> +        report_free_page_completion(vb);
> +}
> +
> +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);
                    
       is size here (integer) intentional?

> +        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;

just thinking if memory for callbacks[3] & names[3] is allocated?

> +                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();
>                  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 fail\n",
> +                                 __func__);
> +                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
> @@ -590,7 +699,7 @@ static int virtballoon_migratepage(struct
> balloon_dev_info *vb_dev_info,
>          spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
>          if (use_sg) {
>                  send_one_sg(vb, vb->inflate_vq, page_address(newpage),
> -                            PAGE_SIZE);
> +                            PAGE_SIZE, 0);
>          } else {
>                  vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
>                  set_page_pfns(vb, vb->pfns, newpage);
> @@ -600,7 +709,7 @@ static int virtballoon_migratepage(struct
> balloon_dev_info *vb_dev_info,
>          balloon_page_delete(page);
>          if (use_sg) {
>                  send_one_sg(vb, vb->deflate_vq, page_address(page),
> -                            PAGE_SIZE);
> +                            PAGE_SIZE, 0);
>          } else {
>                  vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
>                  set_page_pfns(vb, vb->pfns, page);
> @@ -667,6 +776,9 @@ 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);
> @@ -731,6 +843,7 @@ 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);
>  
>          xb_empty(&vb->page_xb);
>          remove_common(vb);
> @@ -785,6 +898,7 @@ 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
> 
>