Linux Virtualization - Jul 2016 - [PATCH v2 repost 7/7] virtio-balloon: tell host vm's free page info

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 at intel.com>
> Cc: Michael S. Tsirkin <mst at redhat.com>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Cc: Vlastimil Babka <vbabka at suse.cz>
> Cc: Mel Gorman <mgorman at techsingularity.net>
> Cc: Paolo Bonzini <pbonzini at redhat.com>
> Cc: Cornelia Huck <cornelia.huck at de.ibm.com>
> Cc: Amit Shah <amit.shah at 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

> >  }
> >
> > +static void update_free_pages_stats(struct virtio_balloon *vb,
> 
> why _stats?
Will change.
> > +	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?
I am no quite sure about this part, I though the virtqueue_kick(vq) will prevent
the buffer from overwrite, I realized it's wrong.
> > +
> > +		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.
I will change this part in v3.
> 
> > +		pfn += vb->pfn_limit;
> > +	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.
Yes, what's you mean by 'validate' that?
> 
> 
> > +	else
> > +		nvqs = virtio_has_feature(vb->vdev,
> > +					  VIRTIO_BALLOON_F_STATS_VQ) ? 3 :
> 2;
> 
> Replace that ? with else too pls.
Will change.

Thanks!
Liang

On Thu, Jul 28, 2016 at 07:50:52AM +0000, Li, Liang Z
wrote:
> > >  }
> > >
> > > +static void update_free_pages_stats(struct virtio_balloon *vb,
> > 
> > why _stats?
> 
> Will change.
> 
> > > +	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?
> 
> I am no quite sure about this part, I though the virtqueue_kick(vq) will
prevent
> the buffer from overwrite, I realized it's wrong.
> 
> > > +
> > > +		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.
> 
> I will change this part in v3.
> 
> > 
> > > +		pfn += vb->pfn_limit;
> > > +	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.
> 
> Yes, what's you mean by 'validate' that?
Either handle misc vq without a stats vq, or
clear VIRTIO_BALLOON_F_MISC_VQ if stats vq is off.
> > 
> > 
> > > +	else
> > > +		nvqs = virtio_has_feature(vb->vdev,
> > > +					  VIRTIO_BALLOON_F_STATS_VQ) ? 3 :
> > 2;
> > 
> > Replace that ? with else too pls.
> 
> Will change.
> 
> Thanks!
> Liang