Re: [Qemu-devel] [PATCH kernel 2/2] virtio-balloon: extend balloon driver to support the new feature

[Michael S. Tsirkin]

On Tue, Apr 19, 2016 at 10:34:34PM +0800, Liang Li wrote:
> Extend the virtio balloon to support the new feature
> VIRTIO_BALLOON_F_GET_FREE_PAGES, so that we can use it to send
> the free page bitmap from guest to QEMU, the free page bitmap will
> be used for live migration optimization.
> 
> Signed-off-by: Liang Li <address@hidden>

Two points:
- please post description of your interface proposals
  to virtio tc comment list
- please split this up
        - feature to use a bitmap for inflate/deflate
        - a 3rd vq which does inflate/deflate in one go

  there seems no reason to use bitmap for free pages
  but not for inflate/deflate

> ---
>  drivers/virtio/virtio_balloon.c     | 100 
> ++++++++++++++++++++++++++++++++++--
>  include/uapi/linux/virtio_balloon.h |   1 +
>  2 files changed, 96 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 7b6d74f..cf17694 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -45,9 +45,17 @@ static int oom_pages = OOM_VBALLOON_DEFAULT_PAGES;
>  module_param(oom_pages, int, S_IRUSR | S_IWUSR);
>  MODULE_PARM_DESC(oom_pages, "pages to free on OOM");
>  
> +extern void get_free_pages(unsigned long *free_page_bitmap,
> +                             unsigned long len, int drop);
> +extern unsigned long get_max_pfn(void);
> +
> +struct cache_drop_ctrl {
> +     u64 ctrl;
> +};
> +
>  struct virtio_balloon {
>       struct virtio_device *vdev;
> -     struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
> +     struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *free_pages_vq;
>  
>       /* The balloon servicing is delegated to a freezable workqueue. */
>       struct work_struct update_balloon_stats_work;
> @@ -77,6 +85,10 @@ struct virtio_balloon {
>       unsigned int num_pfns;
>       u32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];
>  
> +     unsigned long *free_pages;
> +     unsigned long bmap_len;
> +     struct cache_drop_ctrl cache_drop;
> +
>       /* Memory statistics */
>       struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
>  
> @@ -256,6 +268,64 @@ static void update_balloon_stats(struct virtio_balloon 
> *vb)
>                               pages_to_bytes(available));
>  }
>  
> +static void update_free_pages_stats(struct virtio_balloon *vb)
> +{
> +     unsigned long bitmap_bytes, max_pfn;
> +
> +     max_pfn = get_max_pfn();
> +     bitmap_bytes = ALIGN(max_pfn, BITS_PER_LONG) / 8;
> +
> +     if (!vb->free_pages)
> +             vb->free_pages = kzalloc(bitmap_bytes, GFP_KERNEL);
> +     else {
> +             if (bitmap_bytes < vb->bmap_len)
> +                     memset(vb->free_pages, 0, bitmap_bytes);
> +             else {
> +                     kfree(vb->free_pages);
> +                     vb->free_pages = kzalloc(bitmap_bytes, GFP_KERNEL);
> +             }
> +     }
> +     if (!vb->free_pages) {
> +             vb->bmap_len = 0;
> +             return;
> +     }
> +
> +     vb->bmap_len = bitmap_bytes;
> +     get_free_pages(vb->free_pages, max_pfn, vb->cache_drop.ctrl);
> +}
> +
> +static void free_pages_handle_rq(struct virtio_balloon *vb)
> +{
> +     struct virtqueue *vq;
> +     struct scatterlist sg[2];
> +     unsigned int len;
> +     struct cache_drop_ctl *ptr_cache_drop;
> +     struct scatterlist sg_in;
> +
> +     vq = vb->free_pages_vq;
> +     ptr_cache_drop = virtqueue_get_buf(vq, &len);
> +
> +     if (!ptr_cache_drop || len != sizeof(vb->cache_drop))
> +             return;
> +     update_free_pages_stats(vb);
> +     sg_init_table(sg, 2);
> +     sg_set_buf(&sg[0], &(vb->bmap_len), sizeof(vb->bmap_len));
> +     sg_set_buf(&sg[1], vb->free_pages, vb->bmap_len);
> +
> +     sg_init_one(&sg_in, &vb->cache_drop, sizeof(vb->cache_drop));
> +
> +     virtqueue_add_outbuf(vq, &sg[0], 2, vb, GFP_KERNEL);
> +     virtqueue_add_inbuf(vq, &sg_in, 1, &vb->cache_drop, GFP_KERNEL);
> +     virtqueue_kick(vq);
> +}
> +
> +static void free_pages_rq(struct virtqueue *vq)
> +{
> +     struct virtio_balloon *vb = vq->vdev->priv;
> +
> +     free_pages_handle_rq(vb);
> +}
> +
>  /*
>   * While most virtqueues communicate guest-initiated requests to the 
> hypervisor,
>   * the stats queue operates in reverse.  The driver initializes the virtqueue
> @@ -392,16 +462,22 @@ static void update_balloon_size_func(struct work_struct 
> *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" };
> +     struct virtqueue *vqs[4];
> +     vq_callback_t *callbacks[] = { balloon_ack, balloon_ack,
> +                                      stats_request, free_pages_rq };
> +     const char *names[] = { "inflate", "deflate", "stats", "free_pages" };
>       int err, nvqs;
>  
>       /*
>        * We expect two virtqueues: inflate and deflate, and
>        * optionally stat.
>        */
> -     nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
> +     if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_GET_FREE_PAGES))
> +             nvqs = 4;
> +     else
> +             nvqs = virtio_has_feature(vb->vdev,
> +                                       VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
> +
>       err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks, names);
>       if (err)
>               return err;
> @@ -422,6 +498,16 @@ static int init_vqs(struct virtio_balloon *vb)
>                       BUG();
>               virtqueue_kick(vb->stats_vq);
>       }
> +     if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_GET_FREE_PAGES)) {
> +             struct scatterlist sg_in;
> +
> +             vb->free_pages_vq = vqs[3];
> +             sg_init_one(&sg_in, &vb->cache_drop, sizeof(vb->cache_drop));
> +             if (virtqueue_add_inbuf(vb->free_pages_vq, &sg_in, 1,
> +                 &vb->cache_drop, GFP_KERNEL) < 0)
> +                     BUG();
> +             virtqueue_kick(vb->free_pages_vq);
> +     }
>       return 0;
>  }
>  
> @@ -505,6 +591,8 @@ static int virtballoon_probe(struct virtio_device *vdev)
>               goto out;
>       }
>  
> +     vb->bmap_len = 0;
> +     vb->free_pages = NULL;
>       INIT_WORK(&vb->update_balloon_stats_work, update_balloon_stats_func);
>       INIT_WORK(&vb->update_balloon_size_work, update_balloon_size_func);
>       spin_lock_init(&vb->stop_update_lock);
> @@ -567,6 +655,7 @@ static void virtballoon_remove(struct virtio_device *vdev)
>       cancel_work_sync(&vb->update_balloon_stats_work);
>  
>       remove_common(vb);
> +     kfree(vb->free_pages);
>       kfree(vb);
>  }
>  
> @@ -605,6 +694,7 @@ static unsigned int features[] = {
>       VIRTIO_BALLOON_F_MUST_TELL_HOST,
>       VIRTIO_BALLOON_F_STATS_VQ,
>       VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
> +     VIRTIO_BALLOON_F_GET_FREE_PAGES,
>  };
>  
>  static struct virtio_driver virtio_balloon_driver = {
> diff --git a/include/uapi/linux/virtio_balloon.h 
> b/include/uapi/linux/virtio_balloon.h
> index 343d7dd..2b41e4f 100644
> --- a/include/uapi/linux/virtio_balloon.h
> +++ b/include/uapi/linux/virtio_balloon.h
> @@ -34,6 +34,7 @@
>  #define VIRTIO_BALLOON_F_MUST_TELL_HOST      0 /* Tell before reclaiming 
> pages */
>  #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_GET_FREE_PAGES      3 /* Get free page bitmap */
>  
>  /* Size of a PFN in the balloon interface. */
>  #define VIRTIO_BALLOON_PFN_SHIFT 12
> -- 
> 1.8.3.1