Re: [PATCH v2 repost 7/7] virtio-balloon: tell host vm's free page info

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

On Wed, Jul 27, 2016 at 09:23:36AM +0800, Liang Li wrote:
> Support the request for vm's free page information, response with
> a page bitmap. QEMU can make use of this free page bitmap to speed
> up live migration process by skipping process the free pages.
> 
> Signed-off-by: Liang Li <liang.z.li@intel.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
> Cc: Amit Shah <amit.shah@redhat.com>
> ---
>  drivers/virtio/virtio_balloon.c | 104 +++++++++++++++++++++++++++++++++++++---
>  1 file changed, 98 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 2d18ff6..5ca4ad3 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -62,10 +62,13 @@ module_param(oom_pages, int, S_IRUSR | S_IWUSR);
>  MODULE_PARM_DESC(oom_pages, "pages to free on OOM");
>  
>  extern unsigned long get_max_pfn(void);
> +extern int get_free_pages(unsigned long start_pfn, unsigned long end_pfn,
> +		unsigned long *bitmap, unsigned long len);
> +
>  
>  struct virtio_balloon {
>  	struct virtio_device *vdev;
> -	struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
> +	struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *misc_vq;
>  
>  	/* The balloon servicing is delegated to a freezable workqueue. */
>  	struct work_struct update_balloon_stats_work;
> @@ -89,6 +92,8 @@ struct virtio_balloon {
>  	unsigned long pfn_limit;
>  	/* Used to record the processed pfn range */
>  	unsigned long min_pfn, max_pfn, start_pfn, end_pfn;
> +	/* Request header */
> +	struct balloon_req_hdr req_hdr;
>  	/*
>  	 * The pages we've told the Host we're not using are enqueued
>  	 * at vb_dev_info->pages list.
> @@ -373,6 +378,49 @@ static void update_balloon_stats(struct virtio_balloon *vb)
>  				pages_to_bytes(available));
>  }
>  
> +static void update_free_pages_stats(struct virtio_balloon *vb,

why _stats?

> +				unsigned long req_id)
> +{
> +	struct scatterlist sg_in, sg_out;
> +	unsigned long pfn = 0, bmap_len, max_pfn;
> +	struct virtqueue *vq = vb->misc_vq;
> +	struct balloon_bmap_hdr *hdr = vb->bmap_hdr;
> +	int ret = 1;
> +
> +	max_pfn = get_max_pfn();
> +	mutex_lock(&vb->balloon_lock);
> +	while (pfn < max_pfn) {
> +		memset(vb->page_bitmap, 0, vb->bmap_len);
> +		ret = get_free_pages(pfn, pfn + vb->pfn_limit,
> +			vb->page_bitmap, vb->bmap_len * BITS_PER_BYTE);
> +		hdr->cmd = cpu_to_virtio16(vb->vdev, BALLOON_GET_FREE_PAGES);
> +		hdr->page_shift = cpu_to_virtio16(vb->vdev, PAGE_SHIFT);
> +		hdr->req_id = cpu_to_virtio64(vb->vdev, req_id);
> +		hdr->start_pfn = cpu_to_virtio64(vb->vdev, pfn);
> +		bmap_len = vb->pfn_limit / BITS_PER_BYTE;
> +		if (!ret) {
> +			hdr->flag = cpu_to_virtio16(vb->vdev,
> +							BALLOON_FLAG_DONE);
> +			if (pfn + vb->pfn_limit > max_pfn)
> +				bmap_len = (max_pfn - pfn) / BITS_PER_BYTE;
> +		} else
> +			hdr->flag = cpu_to_virtio16(vb->vdev,
> +							BALLOON_FLAG_CONT);
> +		hdr->bmap_len = cpu_to_virtio64(vb->vdev, bmap_len);
> +		sg_init_one(&sg_out, hdr,
> +			 sizeof(struct balloon_bmap_hdr) + bmap_len);

Wait a second. This adds the same buffer multiple times in a loop.
We will overwrite the buffer without waiting for
hypervisor to process it. What did I miss?
> +
> +		virtqueue_add_outbuf(vq, &sg_out, 1, vb, GFP_KERNEL);

this can fail. you want to maybe make sure vq has enough space
before you use it or check error and wait.

> +		virtqueue_kick(vq);

why kick here within loop? wait until done. in fact kick
outside lock is better for smp.

> +		pfn += vb->pfn_limit;
> +	}
> +
> +	sg_init_one(&sg_in, &vb->req_hdr, sizeof(vb->req_hdr));
> +	virtqueue_add_inbuf(vq, &sg_in, 1, &vb->req_hdr, GFP_KERNEL);
> +	virtqueue_kick(vq);
> +	mutex_unlock(&vb->balloon_lock);
> +}
> +
>  /*
>   * While most virtqueues communicate guest-initiated requests to the hypervisor,
>   * the stats queue operates in reverse.  The driver initializes the virtqueue
> @@ -511,18 +559,49 @@ static void update_balloon_size_func(struct work_struct *work)
>  		queue_work(system_freezable_wq, work);
>  }
>  
> +static void misc_handle_rq(struct virtio_balloon *vb)
> +{
> +	struct balloon_req_hdr *ptr_hdr;
> +	unsigned int len;
> +
> +	ptr_hdr = virtqueue_get_buf(vb->misc_vq, &len);
> +	if (!ptr_hdr || len != sizeof(vb->req_hdr))
> +		return;
> +
> +	switch (ptr_hdr->cmd) {
> +	case BALLOON_GET_FREE_PAGES:
> +		update_free_pages_stats(vb, ptr_hdr->param);
> +		break;
> +	default:
> +		break;
> +	}
> +}
> +
> +static void misc_request(struct virtqueue *vq)
> +{
> +	struct virtio_balloon *vb = vq->vdev->priv;
> +
> +	misc_handle_rq(vb);
> +}
> +
>  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, misc_request };
> +	static const char * const names[] = { "inflate", "deflate", "stats",
> +						 "misc" };
>  	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_MISC_VQ))
> +		nvqs = 4;

Does misc vq depend on stats vq feature then? if yes please validate that.


> +	else
> +		nvqs = virtio_has_feature(vb->vdev,
> +					  VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;

Replace that ? with else too pls.

>  	err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks, names);
>  	if (err)
>  		return err;
> @@ -543,6 +622,16 @@ static int init_vqs(struct virtio_balloon *vb)
>  			BUG();
>  		virtqueue_kick(vb->stats_vq);
>  	}
> +	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_MISC_VQ)) {
> +		struct scatterlist sg_in;
> +
> +		vb->misc_vq = vqs[3];
> +		sg_init_one(&sg_in, &vb->req_hdr, sizeof(vb->req_hdr));
> +		if (virtqueue_add_inbuf(vb->misc_vq, &sg_in, 1,
> +		    &vb->req_hdr, GFP_KERNEL) < 0)
> +			BUG();
> +		virtqueue_kick(vb->misc_vq);
> +	}
>  	return 0;
>  }
>  
> @@ -639,8 +728,10 @@ static int virtballoon_probe(struct virtio_device *vdev)
>  	vb->bmap_hdr = kzalloc(hdr_len + vb->bmap_len, GFP_KERNEL);
>  
>  	/* Clear the feature bit if memory allocation fails */
> -	if (!vb->bmap_hdr)
> +	if (!vb->bmap_hdr) {
>  		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_BITMAP);
> +		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_MISC_VQ);
> +	}
>  	else
>  		vb->page_bitmap = vb->bmap_hdr + hdr_len;
>  	mutex_init(&vb->balloon_lock);
> @@ -743,6 +834,7 @@ static unsigned int features[] = {
>  	VIRTIO_BALLOON_F_STATS_VQ,
>  	VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
>  	VIRTIO_BALLOON_F_PAGE_BITMAP,
> +	VIRTIO_BALLOON_F_MISC_VQ,
>  };
>  
>  static struct virtio_driver virtio_balloon_driver = {
> -- 
> 1.9.1