Re: [Qemu-devel] [PATCH v3 2/3] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

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

On Fri, Mar 02, 2018 at 04:47:29PM +0800, Wei Wang wrote:
> The new feature enables the virtio-balloon device to receive hints of
> guest free pages from the free page vq. Callers call the
> free_page_start API to start the reporting, which creates a thread to
> poll for free page hints. The free_page_stop API stops the reporting and
> makes the thread exit.
> 
> Signed-off-by: Wei Wang <wei.w.wang@intel.com>
> Signed-off-by: Liang Li <liang.z.li@intel.com>
> CC: Michael S. Tsirkin <mst@redhat.com>
> CC: Dr. David Alan Gilbert <dgilbert@redhat.com>
> CC: Juan Quintela <quintela@redhat.com>
> ---
>  balloon.c                                       |  49 +++++--
>  hw/virtio/virtio-balloon.c                      | 172 +++++++++++++++++++++---
>  include/hw/virtio/virtio-balloon.h              |  14 +-
>  include/standard-headers/linux/virtio_balloon.h |   7 +
>  include/sysemu/balloon.h                        |  15 ++-
>  5 files changed, 228 insertions(+), 29 deletions(-)
> 
> diff --git a/balloon.c b/balloon.c
> index d8dd6fe..b0b0749 100644
> --- a/balloon.c
> +++ b/balloon.c
> @@ -36,6 +36,9 @@
>  
>  static QEMUBalloonEvent *balloon_event_fn;
>  static QEMUBalloonStatus *balloon_stat_fn;
> +static QEMUBalloonFreePageSupport *balloon_free_page_support_fn;
> +static QEMUBalloonFreePageStart *balloon_free_page_start_fn;
> +static QEMUBalloonFreePageStop *balloon_free_page_stop_fn;
>  static void *balloon_opaque;
>  static bool balloon_inhibited;
>  
> @@ -64,19 +67,42 @@ static bool have_balloon(Error **errp)
>      return true;
>  }
>  
> -int qemu_add_balloon_handler(QEMUBalloonEvent *event_func,
> -                             QEMUBalloonStatus *stat_func, void *opaque)
> +bool balloon_free_page_support(void)
>  {
> -    if (balloon_event_fn || balloon_stat_fn || balloon_opaque) {
> -        /* We're already registered one balloon handler.  How many can
> -         * a guest really have?
> -         */
> -        return -1;
> +    return balloon_free_page_support_fn &&
> +           balloon_free_page_support_fn(balloon_opaque);
> +}
> +
> +void balloon_free_page_start(void)
> +{
> +    balloon_free_page_start_fn(balloon_opaque);
> +}
> +
> +void balloon_free_page_stop(void)
> +{
> +    balloon_free_page_stop_fn(balloon_opaque);
> +}
> +
> +void qemu_add_balloon_handler(QEMUBalloonEvent *event_fn,
> +                              QEMUBalloonStatus *stat_fn,
> +                              QEMUBalloonFreePageSupport *free_page_support_fn,
> +                              QEMUBalloonFreePageStart *free_page_start_fn,
> +                              QEMUBalloonFreePageStop *free_page_stop_fn,
> +                              void *opaque)
> +{
> +    if (balloon_event_fn || balloon_stat_fn || balloon_free_page_support_fn ||
> +        balloon_free_page_start_fn || balloon_free_page_stop_fn ||
> +        balloon_opaque) {
> +        /* We already registered one balloon handler. */
> +        return;
>      }
> -    balloon_event_fn = event_func;
> -    balloon_stat_fn = stat_func;
> +
> +    balloon_event_fn = event_fn;
> +    balloon_stat_fn = stat_fn;
> +    balloon_free_page_support_fn = free_page_support_fn;
> +    balloon_free_page_start_fn = free_page_start_fn;
> +    balloon_free_page_stop_fn = free_page_stop_fn;
>      balloon_opaque = opaque;
> -    return 0;
>  }
>  
>  void qemu_remove_balloon_handler(void *opaque)
> @@ -86,6 +112,9 @@ void qemu_remove_balloon_handler(void *opaque)
>      }
>      balloon_event_fn = NULL;
>      balloon_stat_fn = NULL;
> +    balloon_free_page_support_fn = NULL;
> +    balloon_free_page_start_fn = NULL;
> +    balloon_free_page_stop_fn = NULL;
>      balloon_opaque = NULL;
>  }
>  
> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> index 4822449..4607879 100644
> --- a/hw/virtio/virtio-balloon.c
> +++ b/hw/virtio/virtio-balloon.c
> @@ -31,6 +31,7 @@
>  
>  #include "hw/virtio/virtio-bus.h"
>  #include "hw/virtio/virtio-access.h"
> +#include "migration/misc.h"
>  
>  #define BALLOON_PAGE_SIZE  (1 << VIRTIO_BALLOON_PFN_SHIFT)
>  
> @@ -308,6 +309,100 @@ out:
>      }
>  }
>  
> +static void *virtio_balloon_poll_free_page_hints(void *opaque)
> +{
> +    VirtQueueElement *elem;
> +    VirtIOBalloon *dev = opaque;
> +    VirtQueue *vq = dev->free_page_vq;
> +    uint32_t id;
> +    size_t size;
> +
> +    /*
> +     * Poll the vq till the status changed to STOP. This happens when
> +     * the guest finishes reporting hints or the migration thread actively
> +     * stops the reporting.
> +     */
> +    while (dev->free_page_report_status != FREE_PAGE_REPORT_S_STOP) {
> +        elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
> +        if (!elem) {
> +            continue;
> +        }
> +
> +        if (elem->out_num) {
> +            size = iov_to_buf(elem->out_sg, elem->out_num, 0, &id, sizeof(id));
> +            virtqueue_push(vq, elem, size);
> +            g_free(elem);
> +            if (unlikely(size != sizeof(id))) {
> +                warn_report("%s: received an incorrect cmd id", __func__);
> +                break;
> +            }
> +            if (id == dev->free_page_report_cmd_id) {
> +                dev->free_page_report_status = FREE_PAGE_REPORT_S_START;
> +            } else if (dev->free_page_report_status ==
> +                       FREE_PAGE_REPORT_S_START) {
> +                /*
> +                 * Stop the optimization only when it has started. This avoids
> +                 * obsolete stop sign for the previous command.
> +                 */
> +                dev->free_page_report_status = FREE_PAGE_REPORT_S_STOP;
> +                break;
> +            }
> +        }
> +
> +        if (elem->in_num) {
> +            if (dev->free_page_report_status == FREE_PAGE_REPORT_S_START &&
> +                !dev->poison_val) {
> +                qemu_guest_free_page_hint(elem->in_sg[0].iov_base,
> +                                          elem->in_sg[0].iov_len);
> +            }
> +            virtqueue_push(vq, elem, 0);
> +            g_free(elem);
> +        }
> +    }
> +    return NULL;
> +}
> +
> +static bool virtio_balloon_free_page_support(void *opaque)
> +{
> +    VirtIOBalloon *s = opaque;
> +    VirtIODevice *vdev = VIRTIO_DEVICE(s);
> +
> +    return virtio_vdev_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT);
> +}
> +
> +static void virtio_balloon_free_page_start(void *opaque)
> +{
> +    VirtIOBalloon *s = opaque;
> +    VirtIODevice *vdev = VIRTIO_DEVICE(s);
> +
> +    if (unlikely(s->free_page_report_cmd_id == UINT_MAX)) {
> +        s->free_page_report_cmd_id =
> +                       VIRTIO_BALLOON_FREE_PAGE_REPORT_CMD_ID_MIN;
> +    } else {
> +        s->free_page_report_cmd_id++;
> +    }
> +
> +    s->free_page_report_status = FREE_PAGE_REPORT_S_REQUESTED;
> +    virtio_notify_config(vdev);
> +    qemu_thread_create(&s->free_page_thread, "free_page_optimization_thread",
> +                       virtio_balloon_poll_free_page_hints, s,
> +                       QEMU_THREAD_JOINABLE);
> +}
> +
> +static void virtio_balloon_free_page_stop(void *opaque)
> +{
> +    VirtIOBalloon *s = opaque;
> +    VirtIODevice *vdev = VIRTIO_DEVICE(s);
> +
> +    if (s->free_page_report_status == FREE_PAGE_REPORT_S_STOP) {
> +        return;
> +    }
> +
> +    s->free_page_report_status = FREE_PAGE_REPORT_S_STOP;
> +    virtio_notify_config(vdev);
> +    qemu_thread_join(&s->free_page_thread);
> +}
> +
>  static void virtio_balloon_get_config(VirtIODevice *vdev, uint8_t *config_data)
>  {
>      VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
> @@ -315,6 +410,15 @@ static void virtio_balloon_get_config(VirtIODevice *vdev, uint8_t *config_data)
>  
>      config.num_pages = cpu_to_le32(dev->num_pages);
>      config.actual = cpu_to_le32(dev->actual);
> +    config.poison_val = cpu_to_le32(dev->poison_val);
> +
> +    if (dev->free_page_report_status == FREE_PAGE_REPORT_S_STOP) {
> +        config.free_page_report_cmd_id =
> +                       cpu_to_le32(VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID);
> +    } else {
> +        config.free_page_report_cmd_id =
> +                       cpu_to_le32(dev->free_page_report_cmd_id);
> +    }
>  
>      trace_virtio_balloon_get_config(config.num_pages, config.actual);
>      memcpy(config_data, &config, sizeof(struct virtio_balloon_config));
> @@ -368,6 +472,7 @@ static void virtio_balloon_set_config(VirtIODevice *vdev,
>                          ((ram_addr_t) dev->actual << VIRTIO_BALLOON_PFN_SHIFT),
>                          &error_abort);
>      }
> +    dev->poison_val = le32_to_cpu(config.poison_val);
>      trace_virtio_balloon_set_config(dev->actual, oldactual);
>  }
>  
> @@ -377,6 +482,11 @@ static uint64_t virtio_balloon_get_features(VirtIODevice *vdev, uint64_t f,
>      VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
>      f |= dev->host_features;
>      virtio_add_feature(&f, VIRTIO_BALLOON_F_STATS_VQ);
> +
> +    if (dev->host_features & 1ULL << VIRTIO_BALLOON_F_FREE_PAGE_HINT) {
> +        virtio_add_feature(&f, VIRTIO_BALLOON_F_PAGE_POISON);
> +    }
> +
>      return f;
>  }
>  
> @@ -413,6 +523,18 @@ static int virtio_balloon_post_load_device(void *opaque, int version_id)
>      return 0;
>  }
>  
> +static const VMStateDescription vmstate_virtio_balloon_free_page_report = {
> +    .name = "virtio-balloon-device/free-page-report",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .needed = virtio_balloon_free_page_support,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_UINT32(free_page_report_cmd_id, VirtIOBalloon),
> +        VMSTATE_UINT32(poison_val, VirtIOBalloon),
> +        VMSTATE_END_OF_LIST()
> +    }
> +};
> +
>  static const VMStateDescription vmstate_virtio_balloon_device = {
>      .name = "virtio-balloon-device",
>      .version_id = 1,
> @@ -423,30 +545,30 @@ static const VMStateDescription vmstate_virtio_balloon_device = {
>          VMSTATE_UINT32(actual, VirtIOBalloon),
>          VMSTATE_END_OF_LIST()
>      },
> +    .subsections = (const VMStateDescription * []) {
> +        &vmstate_virtio_balloon_free_page_report,
> +        NULL
> +    }
>  };
>  
>  static void virtio_balloon_device_realize(DeviceState *dev, Error **errp)
>  {
>      VirtIODevice *vdev = VIRTIO_DEVICE(dev);
>      VirtIOBalloon *s = VIRTIO_BALLOON(dev);
> -    int ret;
>  
>      virtio_init(vdev, "virtio-balloon", VIRTIO_ID_BALLOON,
>                  sizeof(struct virtio_balloon_config));
>  
> -    ret = qemu_add_balloon_handler(virtio_balloon_to_target,
> -                                   virtio_balloon_stat, s);
> -
> -    if (ret < 0) {
> -        error_setg(errp, "Only one balloon device is supported");
> -        virtio_cleanup(vdev);
> -        return;
> -    }
> -
>      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);
> -
> +    if (virtio_has_feature(s->host_features,
> +                           VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
> +        s->free_page_vq = virtio_add_queue(vdev, VIRTQUEUE_MAX_SIZE, NULL);
> +        s->free_page_report_status = FREE_PAGE_REPORT_S_STOP;
> +        s->free_page_report_cmd_id =
> +                           VIRTIO_BALLOON_FREE_PAGE_REPORT_CMD_ID_MIN - 1;
> +    }
>      reset_stats(s);
>  }
>  
> @@ -475,11 +597,27 @@ static void virtio_balloon_set_status(VirtIODevice *vdev, uint8_t status)
>  {
>      VirtIOBalloon *s = VIRTIO_BALLOON(vdev);
>  
> -    if (!s->stats_vq_elem && vdev->vm_running &&
> -        (status & VIRTIO_CONFIG_S_DRIVER_OK) && virtqueue_rewind(s->svq, 1)) {
> -        /* poll stats queue for the element we have discarded when the VM
> -         * was stopped */
> -        virtio_balloon_receive_stats(vdev, s->svq);
> +    if (status & VIRTIO_CONFIG_S_DRIVER_OK) {
> +        if (!s->stats_vq_elem && vdev->vm_running &&
> +            virtqueue_rewind(s->svq, 1)) {
> +            /*
> +             * Poll stats queue for the element we have discarded when the VM
> +             * was stopped.
> +             */
> +            virtio_balloon_receive_stats(vdev, s->svq);
> +        }
> +
> +        if (virtio_balloon_free_page_support(s)) {
> +            qemu_add_balloon_handler(virtio_balloon_to_target,
> +                                     virtio_balloon_stat,
> +                                     virtio_balloon_free_page_support,
> +                                     virtio_balloon_free_page_start,
> +                                     virtio_balloon_free_page_stop,
> +                                     s);
> +        } else {
> +            qemu_add_balloon_handler(virtio_balloon_to_target,
> +                                     virtio_balloon_stat, NULL, NULL, NULL, s);
> +        }
>      }
>  }
>  
> @@ -509,6 +647,8 @@ static const VMStateDescription vmstate_virtio_balloon = {
>  static Property virtio_balloon_properties[] = {
>      DEFINE_PROP_BIT("deflate-on-oom", VirtIOBalloon, host_features,
>                      VIRTIO_BALLOON_F_DEFLATE_ON_OOM, false),
> +    DEFINE_PROP_BIT("free-page-hint", VirtIOBalloon, host_features,
> +                    VIRTIO_BALLOON_F_FREE_PAGE_HINT, false),
>      DEFINE_PROP_END_OF_LIST(),
>  };
>  
> diff --git a/include/hw/virtio/virtio-balloon.h b/include/hw/virtio/virtio-balloon.h
> index 1ea13bd..ce77382 100644
> --- a/include/hw/virtio/virtio-balloon.h
> +++ b/include/hw/virtio/virtio-balloon.h
> @@ -23,6 +23,8 @@
>  #define VIRTIO_BALLOON(obj) \
>          OBJECT_CHECK(VirtIOBalloon, (obj), TYPE_VIRTIO_BALLOON)
>  
> +#define VIRTIO_BALLOON_FREE_PAGE_REPORT_CMD_ID_MIN 0x80000000
> +
>  typedef struct virtio_balloon_stat VirtIOBalloonStat;
>  
>  typedef struct virtio_balloon_stat_modern {
> @@ -31,15 +33,25 @@ typedef struct virtio_balloon_stat_modern {
>         uint64_t val;
>  } VirtIOBalloonStatModern;
>  
> +enum virtio_balloon_free_page_report_status {
> +    FREE_PAGE_REPORT_S_REQUESTED,
> +    FREE_PAGE_REPORT_S_START,
> +    FREE_PAGE_REPORT_S_STOP,
> +};
> +
>  typedef struct VirtIOBalloon {
>      VirtIODevice parent_obj;
> -    VirtQueue *ivq, *dvq, *svq;
> +    VirtQueue *ivq, *dvq, *svq, *free_page_vq;
> +    uint32_t free_page_report_status;
>      uint32_t num_pages;
>      uint32_t actual;
> +    uint32_t free_page_report_cmd_id;
> +    uint32_t poison_val;
>      uint64_t stats[VIRTIO_BALLOON_S_NR];
>      VirtQueueElement *stats_vq_elem;
>      size_t stats_vq_offset;
>      QEMUTimer *stats_timer;
> +    QemuThread free_page_thread;
>      int64_t stats_last_update;
>      int64_t stats_poll_interval;
>      uint32_t host_features;
> diff --git a/include/standard-headers/linux/virtio_balloon.h b/include/standard-headers/linux/virtio_balloon.h
> index 7b0a41b..f89e80f 100644
> --- a/include/standard-headers/linux/virtio_balloon.h
> +++ b/include/standard-headers/linux/virtio_balloon.h
> @@ -34,15 +34,22 @@
>  #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_FREE_PAGE_HINT 3 /* VQ to report free pages */
> +#define VIRTIO_BALLOON_F_PAGE_POISON	4 /* Guest is using page poisoning */
>  
>  /* Size of a PFN in the balloon interface. */
>  #define VIRTIO_BALLOON_PFN_SHIFT 12
>  
> +#define VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID 0
>  struct virtio_balloon_config {
>  	/* Number of pages host wants Guest to give up. */
>  	uint32_t num_pages;
>  	/* Number of pages we've actually got in balloon. */
>  	uint32_t actual;
> +	/* Free page report command id, readonly by guest */
> +	uint32_t free_page_report_cmd_id;
> +	/* Stores PAGE_POISON if page poisoning is in use */
> +	uint32_t poison_val;
>  };
>  
>  #define VIRTIO_BALLOON_S_SWAP_IN  0   /* Amount of memory swapped in */
> diff --git a/include/sysemu/balloon.h b/include/sysemu/balloon.h
> index af49e19..16a2aae 100644
> --- a/include/sysemu/balloon.h
> +++ b/include/sysemu/balloon.h
> @@ -18,11 +18,22 @@
>  
>  typedef void (QEMUBalloonEvent)(void *opaque, ram_addr_t target);
>  typedef void (QEMUBalloonStatus)(void *opaque, BalloonInfo *info);
> +typedef bool (QEMUBalloonFreePageSupport)(void *opaque);
> +typedef void (QEMUBalloonFreePageStart)(void *opaque);
> +typedef void (QEMUBalloonFreePageStop)(void *opaque);

Could you add some documentation about these?
E.g. I think the assumption made here is that all memory
is write-protected when QEMUBalloonFreePageStart runs.


>  
> -int qemu_add_balloon_handler(QEMUBalloonEvent *event_func,
> -			     QEMUBalloonStatus *stat_func, void *opaque);
>  void qemu_remove_balloon_handler(void *opaque);
>  bool qemu_balloon_is_inhibited(void);
>  void qemu_balloon_inhibit(bool state);
> +bool balloon_free_page_support(void);
> +void balloon_free_page_start(void);
> +void balloon_free_page_stop(void);
> +
> +void qemu_add_balloon_handler(QEMUBalloonEvent *event_fn,
> +                              QEMUBalloonStatus *stat_fn,
> +                              QEMUBalloonFreePageSupport *free_page_support_fn,
> +                              QEMUBalloonFreePageStart *free_page_start_fn,
> +                              QEMUBalloonFreePageStop *free_page_stop_fn,
> +                              void *opaque);
>  
>  #endif
> -- 
> 1.8.3.1