Re: [Qemu-devel] [QEMU 2/7] virtio-balloon: add drop cache support

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

On Mon, Jun 13, 2016 at 06:16:44PM +0800, Liang Li wrote:
> virtio-balloon can make use of the amount of free memory to determine
> the amount of memory to be filled in the balloon, but the amount of
> free memory will be effected by the page cache, which can be reclaimed.
> Drop the cache before getting the amount of free memory will be very
> helpful to relect the exact amount of memroy that can be reclaimed.

Can't we just extend stats to report "reclaimable" memory?

> This patch add a new feature to the balloon device to support this
> operation, hypervisor can request the VM to drop it's cache, so as to
> reclaim more memory.
> 
> Signed-off-by: Liang Li <liang.z.li@intel.com>
> ---
>  balloon.c                                       | 10 ++-
>  hw/virtio/virtio-balloon.c                      | 85 ++++++++++++++++++++++++-
>  include/hw/virtio/virtio-balloon.h              | 19 +++++-
>  include/standard-headers/linux/virtio_balloon.h |  1 +
>  include/sysemu/balloon.h                        |  5 +-
>  5 files changed, 115 insertions(+), 5 deletions(-)
> 
> diff --git a/balloon.c b/balloon.c
> index f2ef50c..0fb34bf 100644
> --- a/balloon.c
> +++ b/balloon.c
> @@ -36,6 +36,7 @@
>  
>  static QEMUBalloonEvent *balloon_event_fn;
>  static QEMUBalloonStatus *balloon_stat_fn;
> +static QEMUBalloonDropCache *balloon_drop_cache_fn;
>  static void *balloon_opaque;
>  static bool balloon_inhibited;
>  
> @@ -65,9 +66,12 @@ static bool have_balloon(Error **errp)
>  }
>  
>  int qemu_add_balloon_handler(QEMUBalloonEvent *event_func,
> -                             QEMUBalloonStatus *stat_func, void *opaque)
> +                             QEMUBalloonStatus *stat_func,
> +                             QEMUBalloonDropCache *drop_cache_func,
> +                             void *opaque)
>  {
> -    if (balloon_event_fn || balloon_stat_fn || balloon_opaque) {
> +    if (balloon_event_fn || balloon_stat_fn || balloon_drop_cache_fn
> +        || balloon_opaque) {
>          /* We're already registered one balloon handler.  How many can
>           * a guest really have?
>           */
> @@ -75,6 +79,7 @@ int qemu_add_balloon_handler(QEMUBalloonEvent *event_func,
>      }
>      balloon_event_fn = event_func;
>      balloon_stat_fn = stat_func;
> +    balloon_drop_cache_fn = drop_cache_func;
>      balloon_opaque = opaque;
>      return 0;
>  }
> @@ -86,6 +91,7 @@ void qemu_remove_balloon_handler(void *opaque)
>      }
>      balloon_event_fn = NULL;
>      balloon_stat_fn = NULL;
> +    balloon_drop_cache_fn = NULL;
>      balloon_opaque = NULL;
>  }
>  
> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> index 8cf74c2..4757ba5 100644
> --- a/hw/virtio/virtio-balloon.c
> +++ b/hw/virtio/virtio-balloon.c
> @@ -36,6 +36,10 @@
>  
>  #define BALLOON_PAGE_SIZE  (1 << VIRTIO_BALLOON_PFN_SHIFT)
>  
> +enum balloon_req_id {
> +       BALLOON_DROP_CACHE,
> +};
> +
>  static void balloon_page(void *addr, int deflate)
>  {
>  #if defined(__linux__)
> @@ -154,6 +158,12 @@ static bool balloon_page_bitmap_supported(const VirtIOBalloon *s)
>      return virtio_vdev_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_BITMAP);
>  }
>  
> +static bool balloon_misc_supported(const VirtIOBalloon *s)
> +{
> +    VirtIODevice *vdev = VIRTIO_DEVICE(s);
> +    return virtio_vdev_has_feature(vdev, VIRTIO_BALLOON_F_MISC);
> +}
> +
>  static bool balloon_stats_enabled(const VirtIOBalloon *s)
>  {
>      return s->stats_poll_interval > 0;
> @@ -420,6 +430,39 @@ out:
>      }
>  }
>  
> +static void virtio_balloon_handle_resp(VirtIODevice *vdev, VirtQueue *vq)
> +{
> +    VirtIOBalloon *s = VIRTIO_BALLOON(vdev);
> +    VirtQueueElement *elem;
> +    size_t offset = 0;
> +    uint32_t tmp32, id = 0;
> +
> +    elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
> +    if (!elem) {
> +        s->req_status = REQ_ERROR;
> +        return;
> +    }
> +
> +    s->misc_vq_elem = elem;
> +
> +    if (!elem->out_num) {
> +        return;
> +    }
> +
> +    iov_to_buf(elem->out_sg, elem->out_num, offset,
> +               &tmp32, sizeof(uint32_t));
> +    id = virtio_ldl_p(vdev, &tmp32);
> +    offset += sizeof(uint32_t);
> +    switch (id) {
> +    case BALLOON_DROP_CACHE:
> +        s->req_status = REQ_DONE;
> +        break;
> +    default:
> +        break;
> +    }
> +
> +}
> +
>  static void virtio_balloon_get_config(VirtIODevice *vdev, uint8_t *config_data)
>  {
>      VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
> @@ -490,6 +533,7 @@ static uint64_t virtio_balloon_get_features(VirtIODevice *vdev, uint64_t f,
>      f |= dev->host_features;
>      virtio_add_feature(&f, VIRTIO_BALLOON_F_STATS_VQ);
>      virtio_add_feature(&f, VIRTIO_BALLOON_F_PAGE_BITMAP);
> +    virtio_add_feature(&f, VIRTIO_BALLOON_F_MISC);
>      return f;
>  }
>  
> @@ -500,6 +544,36 @@ static void virtio_balloon_stat(void *opaque, BalloonInfo *info)
>                                               VIRTIO_BALLOON_PFN_SHIFT);
>  }
>  
> +static int virtio_balloon_drop_cache(void *opaque, unsigned long type)
> +{
> +    VirtIOBalloon *s = opaque;
> +    VirtIODevice *vdev = VIRTIO_DEVICE(s);
> +    VirtQueueElement *elem = s->misc_vq_elem;
> +    int len;
> +
> +    if (!balloon_misc_supported(s)) {
> +        return REQ_UNSUPPORT;
> +    }
> +
> +    if (elem == NULL || !elem->in_num) {
> +        elem = virtqueue_pop(s->mvq, sizeof(VirtQueueElement));
> +        if (!elem) {
> +            return REQ_ERROR;
> +        }
> +        s->misc_vq_elem = elem;
> +    }
> +    s->misc_req.id = BALLOON_DROP_CACHE;
> +    s->misc_req.param = type;
> +    len = iov_from_buf(elem->in_sg, elem->in_num, 0, &s->misc_req,
> +                       sizeof(s->misc_req));
> +    virtqueue_push(s->mvq, elem, len);
> +    virtio_notify(vdev, s->mvq);
> +    g_free(s->misc_vq_elem);
> +    s->misc_vq_elem = NULL;
> +
> +    return REQ_DONE;
> +}
> +
>  static void virtio_balloon_to_target(void *opaque, ram_addr_t target)
>  {
>      VirtIOBalloon *dev = VIRTIO_BALLOON(opaque);
> @@ -562,7 +636,8 @@ static void virtio_balloon_device_realize(DeviceState *dev, Error **errp)
>                  sizeof(struct virtio_balloon_config));
>  
>      ret = qemu_add_balloon_handler(virtio_balloon_to_target,
> -                                   virtio_balloon_stat, s);
> +                                   virtio_balloon_stat,
> +                                   virtio_balloon_drop_cache, s);
>  
>      if (ret < 0) {
>          error_setg(errp, "Only one balloon device is supported");
> @@ -573,8 +648,10 @@ static void virtio_balloon_device_realize(DeviceState *dev, Error **errp)
>      s->ivq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output);
>      s->dvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output);
>      s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats);
> +    s->mvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_resp);
>  
>      reset_stats(s);
> +    s->req_status = REQ_INIT;
>  
>      register_savevm(dev, "virtio-balloon", -1, 1,
>                      virtio_balloon_save, virtio_balloon_load, s);
> @@ -599,6 +676,12 @@ static void virtio_balloon_device_reset(VirtIODevice *vdev)
>          g_free(s->stats_vq_elem);
>          s->stats_vq_elem = NULL;
>      }
> +
> +    if (s->misc_vq_elem != NULL) {
> +        g_free(s->misc_vq_elem);
> +        s->misc_vq_elem = NULL;
> +    }
> +    s->req_status = REQ_INIT;
>  }
>  
>  static void virtio_balloon_instance_init(Object *obj)
> diff --git a/include/hw/virtio/virtio-balloon.h b/include/hw/virtio/virtio-balloon.h
> index 35f62ac..a21bb45 100644
> --- a/include/hw/virtio/virtio-balloon.h
> +++ b/include/hw/virtio/virtio-balloon.h
> @@ -23,6 +23,20 @@
>  #define VIRTIO_BALLOON(obj) \
>          OBJECT_CHECK(VirtIOBalloon, (obj), TYPE_VIRTIO_BALLOON)
>  
> +typedef enum {
> +    REQ_INIT,
> +    REQ_ON_GOING,
> +    REQ_DONE,
> +    REQ_ERROR,
> +    REQ_INVALID_PARAM,
> +    REQ_UNSUPPORT,
> +} BalloonReqStatus;
> +
> +typedef struct GetFreePageReq {
> +    uint32_t id;
> +    uint32_t param;
> +} MiscReq;
> +
>  typedef struct virtio_balloon_stat VirtIOBalloonStat;
>  
>  typedef struct virtio_balloon_stat_modern {
> @@ -33,16 +47,19 @@ typedef struct virtio_balloon_stat_modern {
>  
>  typedef struct VirtIOBalloon {
>      VirtIODevice parent_obj;
> -    VirtQueue *ivq, *dvq, *svq;
> +    VirtQueue *ivq, *dvq, *svq, *mvq;
>      uint32_t num_pages;
>      uint32_t actual;
>      uint64_t stats[VIRTIO_BALLOON_S_NR];
>      VirtQueueElement *stats_vq_elem;
> +    VirtQueueElement *misc_vq_elem;
>      size_t stats_vq_offset;
>      QEMUTimer *stats_timer;
>      int64_t stats_last_update;
>      int64_t stats_poll_interval;
>      uint32_t host_features;
> +    MiscReq misc_req;
> +    BalloonReqStatus req_status;
>  } VirtIOBalloon;
>  
>  #endif
> diff --git a/include/standard-headers/linux/virtio_balloon.h b/include/standard-headers/linux/virtio_balloon.h
> index 7c9686c..c8b254f 100644
> --- a/include/standard-headers/linux/virtio_balloon.h
> +++ b/include/standard-headers/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_PAGE_BITMAP  3 /* Use page bitmap to send page info */
> +#define VIRTIO_BALLOON_F_MISC    4 /* Send request and get misc info */
>  
>  /* Size of a PFN in the balloon interface. */
>  #define VIRTIO_BALLOON_PFN_SHIFT 12
> diff --git a/include/sysemu/balloon.h b/include/sysemu/balloon.h
> index 3f976b4..0e85f2b 100644
> --- a/include/sysemu/balloon.h
> +++ b/include/sysemu/balloon.h
> @@ -18,9 +18,12 @@
>  
>  typedef void (QEMUBalloonEvent)(void *opaque, ram_addr_t target);
>  typedef void (QEMUBalloonStatus)(void *opaque, BalloonInfo *info);
> +typedef int (QEMUBalloonDropCache)(void *opaque, unsigned long ctrl);
>  
>  int qemu_add_balloon_handler(QEMUBalloonEvent *event_func,
> -			     QEMUBalloonStatus *stat_func, void *opaque);
> +                             QEMUBalloonStatus *stat_func,
> +                             QEMUBalloonDropCache *drop_cache_func,
> +                             void *opaque);
>  void qemu_remove_balloon_handler(void *opaque);
>  bool qemu_balloon_is_inhibited(void);
>  void qemu_balloon_inhibit(bool state);
> -- 
> 1.9.1