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    SubjectRe: [RFC qemu 2/4] virtio-balloon: Add a new feature to balloon device
    On Thu, Mar 03, 2016 at 06:44:26PM +0800, Liang Li wrote:
    > Extend the virtio balloon device to support a new feature, this
    > new feature can help to get guest's free pages information, which
    > can be used for live migration optimzation.
    >
    > Signed-off-by: Liang Li <liang.z.li@intel.com>

    I don't understand why we need a new interface.
    Balloon already sends free pages to host.
    Just teach host to skip these pages.

    Maybe instead of starting with code, you
    should send a high level description to the
    virtio tc for consideration?

    You can do it through the mailing list or
    using the web form:
    http://www.oasis-open.org/committees/comments/form.php?wg_abbrev=virtio


    > ---
    > balloon.c | 30 ++++++++-
    > hw/virtio/virtio-balloon.c | 81 ++++++++++++++++++++++++-
    > include/hw/virtio/virtio-balloon.h | 17 +++++-
    > include/standard-headers/linux/virtio_balloon.h | 1 +
    > include/sysemu/balloon.h | 10 ++-
    > 5 files changed, 134 insertions(+), 5 deletions(-)
    >
    > diff --git a/balloon.c b/balloon.c
    > index f2ef50c..a37717e 100644
    > --- a/balloon.c
    > +++ b/balloon.c
    > @@ -36,6 +36,7 @@
    >
    > static QEMUBalloonEvent *balloon_event_fn;
    > static QEMUBalloonStatus *balloon_stat_fn;
    > +static QEMUBalloonFreePages *balloon_free_pages_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,
    > + QEMUBalloonFreePages *free_pages_func,
    > + void *opaque)
    > {
    > - if (balloon_event_fn || balloon_stat_fn || balloon_opaque) {
    > + if (balloon_event_fn || balloon_stat_fn || balloon_free_pages_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_free_pages_fn = free_pages_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_free_pages_fn = NULL;
    > balloon_opaque = NULL;
    > }
    >
    > @@ -116,3 +122,23 @@ void qmp_balloon(int64_t target, Error **errp)
    > trace_balloon_event(balloon_opaque, target);
    > balloon_event_fn(balloon_opaque, target);
    > }
    > +
    > +bool balloon_free_pages_support(void)
    > +{
    > + return balloon_free_pages_fn ? true : false;
    > +}
    > +
    > +int balloon_get_free_pages(unsigned long *free_pages_bitmap,
    > + unsigned long *free_pages_count)
    > +{
    > + if (!balloon_free_pages_fn) {
    > + return -1;
    > + }
    > +
    > + if (!free_pages_bitmap || !free_pages_count) {
    > + return -1;
    > + }
    > +
    > + return balloon_free_pages_fn(balloon_opaque,
    > + free_pages_bitmap, free_pages_count);
    > + }
    > diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
    > index e9c30e9..a5b9d08 100644
    > --- a/hw/virtio/virtio-balloon.c
    > +++ b/hw/virtio/virtio-balloon.c
    > @@ -76,6 +76,12 @@ static bool balloon_stats_supported(const VirtIOBalloon *s)
    > return virtio_vdev_has_feature(vdev, VIRTIO_BALLOON_F_STATS_VQ);
    > }
    >
    > +static bool balloon_free_pages_supported(const VirtIOBalloon *s)
    > +{
    > + VirtIODevice *vdev = VIRTIO_DEVICE(s);
    > + return virtio_vdev_has_feature(vdev, VIRTIO_BALLOON_F_GET_FREE_PAGES);
    > +}
    > +
    > static bool balloon_stats_enabled(const VirtIOBalloon *s)
    > {
    > return s->stats_poll_interval > 0;
    > @@ -293,6 +299,37 @@ out:
    > }
    > }
    >
    > +static void virtio_balloon_get_free_pages(VirtIODevice *vdev, VirtQueue *vq)
    > +{
    > + VirtIOBalloon *s = VIRTIO_BALLOON(vdev);
    > + VirtQueueElement *elem;
    > + size_t offset = 0;
    > + uint64_t bitmap_bytes = 0, free_pages_count = 0;
    > +
    > + elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
    > + if (!elem) {
    > + return;
    > + }
    > + s->free_pages_vq_elem = elem;
    > +
    > + if (!elem->out_num) {
    > + return;
    > + }
    > +
    > + iov_to_buf(elem->out_sg, elem->out_num, offset,
    > + &free_pages_count, sizeof(uint64_t));
    > +
    > + offset += sizeof(uint64_t);
    > + iov_to_buf(elem->out_sg, elem->out_num, offset,
    > + &bitmap_bytes, sizeof(uint64_t));
    > +
    > + offset += sizeof(uint64_t);
    > + iov_to_buf(elem->out_sg, elem->out_num, offset,
    > + s->free_pages_bitmap, bitmap_bytes);
    > + s->req_status = DONE;
    > + s->free_pages_count = free_pages_count;
    > +}
    > +
    > static void virtio_balloon_get_config(VirtIODevice *vdev, uint8_t *config_data)
    > {
    > VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
    > @@ -362,6 +399,7 @@ 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);
    > + virtio_add_feature(&f, VIRTIO_BALLOON_F_GET_FREE_PAGES);
    > return f;
    > }
    >
    > @@ -372,6 +410,45 @@ static void virtio_balloon_stat(void *opaque, BalloonInfo *info)
    > VIRTIO_BALLOON_PFN_SHIFT);
    > }
    >
    > +static int virtio_balloon_free_pages(void *opaque,
    > + unsigned long *free_pages_bitmap,
    > + unsigned long *free_pages_count)
    > +{
    > + VirtIOBalloon *s = opaque;
    > + VirtIODevice *vdev = VIRTIO_DEVICE(s);
    > + VirtQueueElement *elem = s->free_pages_vq_elem;
    > + int len;
    > +
    > + if (!balloon_free_pages_supported(s)) {
    > + return -1;
    > + }
    > +
    > + if (s->req_status == NOT_STARTED) {
    > + s->free_pages_bitmap = free_pages_bitmap;
    > + s->req_status = STARTED;
    > + s->mem_layout.low_mem = pc_get_lowmem(PC_MACHINE(current_machine));
    > + if (!elem->in_num) {
    > + elem = virtqueue_pop(s->fvq, sizeof(VirtQueueElement));
    > + if (!elem) {
    > + return 0;
    > + }
    > + s->free_pages_vq_elem = elem;
    > + }
    > + len = iov_from_buf(elem->in_sg, elem->in_num, 0, &s->mem_layout,
    > + sizeof(s->mem_layout));
    > + virtqueue_push(s->fvq, elem, len);
    > + virtio_notify(vdev, s->fvq);
    > + return 0;
    > + } else if (s->req_status == STARTED) {
    > + return 0;
    > + } else if (s->req_status == DONE) {
    > + *free_pages_count = s->free_pages_count;
    > + s->req_status = NOT_STARTED;
    > + }
    > +
    > + return 1;
    > +}
    > +
    > static void virtio_balloon_to_target(void *opaque, ram_addr_t target)
    > {
    > VirtIOBalloon *dev = VIRTIO_BALLOON(opaque);
    > @@ -429,7 +506,8 @@ 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_free_pages, s);
    >
    > if (ret < 0) {
    > error_setg(errp, "Only one balloon device is supported");
    > @@ -440,6 +518,7 @@ 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->fvq = virtio_add_queue(vdev, 128, virtio_balloon_get_free_pages);
    >
    > reset_stats(s);
    >
    > diff --git a/include/hw/virtio/virtio-balloon.h b/include/hw/virtio/virtio-balloon.h
    > index 35f62ac..fc173e4 100644
    > --- a/include/hw/virtio/virtio-balloon.h
    > +++ b/include/hw/virtio/virtio-balloon.h
    > @@ -23,6 +23,16 @@
    > #define VIRTIO_BALLOON(obj) \
    > OBJECT_CHECK(VirtIOBalloon, (obj), TYPE_VIRTIO_BALLOON)
    >
    > +typedef enum virtio_req_status {
    > + NOT_STARTED,
    > + STARTED,
    > + DONE,
    > +} VIRTIO_REQ_STATUS;
    > +
    > +typedef struct MemLayout {
    > + uint64_t low_mem;
    > +} MemLayout;
    > +
    > typedef struct virtio_balloon_stat VirtIOBalloonStat;
    >
    > typedef struct virtio_balloon_stat_modern {
    > @@ -33,16 +43,21 @@ typedef struct virtio_balloon_stat_modern {
    >
    > typedef struct VirtIOBalloon {
    > VirtIODevice parent_obj;
    > - VirtQueue *ivq, *dvq, *svq;
    > + VirtQueue *ivq, *dvq, *svq, *fvq;
    > uint32_t num_pages;
    > uint32_t actual;
    > uint64_t stats[VIRTIO_BALLOON_S_NR];
    > VirtQueueElement *stats_vq_elem;
    > + VirtQueueElement *free_pages_vq_elem;
    > size_t stats_vq_offset;
    > QEMUTimer *stats_timer;
    > int64_t stats_last_update;
    > int64_t stats_poll_interval;
    > uint32_t host_features;
    > + uint64_t *free_pages_bitmap;
    > + uint64_t free_pages_count;
    > + MemLayout mem_layout;
    > + VIRTIO_REQ_STATUS req_status;
    > } VirtIOBalloon;
    >
    > #endif
    > diff --git a/include/standard-headers/linux/virtio_balloon.h b/include/standard-headers/linux/virtio_balloon.h
    > index 2e2a6dc..95b7d0c 100644
    > --- a/include/standard-headers/linux/virtio_balloon.h
    > +++ b/include/standard-headers/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 the free pages bitmap */
    >
    > /* 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..205b272 100644
    > --- a/include/sysemu/balloon.h
    > +++ b/include/sysemu/balloon.h
    > @@ -18,11 +18,19 @@
    >
    > typedef void (QEMUBalloonEvent)(void *opaque, ram_addr_t target);
    > typedef void (QEMUBalloonStatus)(void *opaque, BalloonInfo *info);
    > +typedef int (QEMUBalloonFreePages)(void *opaque,
    > + unsigned long *free_pages_bitmap,
    > + unsigned long *free_pages_count);
    >
    > int qemu_add_balloon_handler(QEMUBalloonEvent *event_func,
    > - QEMUBalloonStatus *stat_func, void *opaque);
    > + QEMUBalloonStatus *stat_func,
    > + QEMUBalloonFreePages *free_pages_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_pages_support(void);
    > +int balloon_get_free_pages(unsigned long *free_pages_bitmap,
    > + unsigned long *free_pages_count);
    >
    > #endif
    > --
    > 1.8.3.1

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