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

From: Michael S. Tsirkin
Date: Tue Apr 19 2016 - 12:19:07 EST

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In reply to: Liang Li: "[PATCH kernel 2/2] virtio-balloon: extend balloon driver to support the new feature"
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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 <liang.z.li@xxxxxxxxx>

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

Next message: Michael S. Tsirkin: "Re: [PATCH RFC] fixup! virtio: convert to use DMA api"
Previous message: Ezequiel Garcia: "Re: [PATCH v2 3/3] leds: gpio: Support the "panic-indicator" firmware property"
In reply to: Liang Li: "[PATCH kernel 2/2] virtio-balloon: extend balloon driver to support the new feature"
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