Re: [QEMU Patch] virtio-baloon: Support for page hinting

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

On Wed, Jul 10, 2019 at 03:53:03PM -0400, Nitesh Narayan Lal wrote:
> Enables QEMU to perform madvise free on the memory range reported
> by the vm.
> 
> Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>

Missing second "l" in the subject :)

> ---
>  hw/virtio/trace-events                        |  1 +
>  hw/virtio/virtio-balloon.c                    | 59 +++++++++++++++++++
>  include/hw/virtio/virtio-balloon.h            |  2 +-
>  include/qemu/osdep.h                          |  7 +++
>  .../standard-headers/linux/virtio_balloon.h   |  1 +
>  5 files changed, 69 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/virtio/trace-events b/hw/virtio/trace-events
> index e28ba48da6..f703a22d36 100644
> --- a/hw/virtio/trace-events
> +++ b/hw/virtio/trace-events
> @@ -46,6 +46,7 @@ virtio_balloon_handle_output(const char *name, uint64_t gpa) "section name: %s g
>  virtio_balloon_get_config(uint32_t num_pages, uint32_t actual) "num_pages: %d actual: %d"
>  virtio_balloon_set_config(uint32_t actual, uint32_t oldactual) "actual: %d oldactual: %d"
>  virtio_balloon_to_target(uint64_t target, uint32_t num_pages) "balloon target: 0x%"PRIx64" num_pages: %d"
> +virtio_balloon_hinting_request(unsigned long pfn, unsigned int num_pages) "Guest page hinting request PFN:%lu size: %d"
>  
>  # virtio-mmio.c
>  virtio_mmio_read(uint64_t offset) "virtio_mmio_read offset 0x%" PRIx64
> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> index 2112874055..5d186707b5 100644
> --- a/hw/virtio/virtio-balloon.c
> +++ b/hw/virtio/virtio-balloon.c
> @@ -34,6 +34,9 @@
>  
>  #define BALLOON_PAGE_SIZE  (1 << VIRTIO_BALLOON_PFN_SHIFT)
>  
> +#define VIRTIO_BALLOON_PAGE_HINTING_MAX_PAGES	16
> +void free_mem_range(uint64_t addr, uint64_t len);
> +
>  struct PartiallyBalloonedPage {
>      RAMBlock *rb;
>      ram_addr_t base;
> @@ -328,6 +331,58 @@ static void balloon_stats_set_poll_interval(Object *obj, Visitor *v,
>      balloon_stats_change_timer(s, 0);
>  }
>  
> +void free_mem_range(uint64_t addr, uint64_t len)
> +{
> +    int ret = 0;
> +    void *hvaddr_to_free;
> +    MemoryRegionSection mrs = memory_region_find(get_system_memory(),
> +                                                 addr, 1);
> +    if (!mrs.mr) {
> +	warn_report("%s:No memory is mapped at address 0x%lu", __func__, addr);
> +        return;
> +    }
> +
> +    if (!memory_region_is_ram(mrs.mr) && !memory_region_is_romd(mrs.mr)) {
> +	warn_report("%s:Memory at address 0x%s is not RAM:0x%lu", __func__,
> +		    HWADDR_PRIx, addr);
> +        memory_region_unref(mrs.mr);
> +        return;
> +    }
> +
> +    hvaddr_to_free = qemu_map_ram_ptr(mrs.mr->ram_block, mrs.offset_within_region);
> +    trace_virtio_balloon_hinting_request(addr, len);
> +    ret = qemu_madvise(hvaddr_to_free,len, QEMU_MADV_FREE);
> +    if (ret == -1) {
> +	warn_report("%s: Madvise failed with error:%d", __func__, ret);
> +    }
> +}
> +
> +static void virtio_balloon_handle_page_hinting(VirtIODevice *vdev,
> +					       VirtQueue *vq)
> +{
> +    VirtQueueElement *elem;
> +    size_t offset = 0;
> +    uint64_t gpa, len;
> +    elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
> +    if (!elem) {
> +        return;
> +    }
> +    /* For pending hints which are < max_pages(16), 'gpa != 0' ensures that we
> +     * only read the buffer which holds a valid PFN value.
> +     * TODO: Find a better way to do this.

Indeed. In fact, what is wrong with passing the gpa as
part of the element itself?

> +     */
> +    while (iov_to_buf(elem->out_sg, elem->out_num, offset, &gpa, 8) == 8 && gpa != 0) {
> +	offset += 8;
> +	offset += iov_to_buf(elem->out_sg, elem->out_num, offset, &len, 8);
> +	if (!qemu_balloon_is_inhibited()) {
> +	    free_mem_range(gpa, len);
> +	}
> +    }
> +    virtqueue_push(vq, elem, offset);
> +    virtio_notify(vdev, vq);
> +    g_free(elem);
> +}
> +
>  static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
>  {
>      VirtIOBalloon *s = VIRTIO_BALLOON(vdev);
> @@ -694,6 +749,7 @@ 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_HINTING);
>  
>      return f;
>  }
> @@ -780,6 +836,7 @@ 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->hvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_page_hinting);
>  
>      if (virtio_has_feature(s->host_features,
>                             VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
> @@ -875,6 +932,8 @@ static void virtio_balloon_instance_init(Object *obj)
>  
>      object_property_add(obj, "guest-stats", "guest statistics",
>                          balloon_stats_get_all, NULL, NULL, s, NULL);
> +    object_property_add(obj, "guest-page-hinting", "guest page hinting",
> +                        NULL, NULL, NULL, s, NULL);
>  
>      object_property_add(obj, "guest-stats-polling-interval", "int",
>                          balloon_stats_get_poll_interval,
> diff --git a/include/hw/virtio/virtio-balloon.h b/include/hw/virtio/virtio-balloon.h
> index 1afafb12f6..a58b24fdf2 100644
> --- a/include/hw/virtio/virtio-balloon.h
> +++ b/include/hw/virtio/virtio-balloon.h
> @@ -44,7 +44,7 @@ enum virtio_balloon_free_page_report_status {
>  
>  typedef struct VirtIOBalloon {
>      VirtIODevice parent_obj;
> -    VirtQueue *ivq, *dvq, *svq, *free_page_vq;
> +    VirtQueue *ivq, *dvq, *svq, *free_page_vq, *hvq;
>      uint32_t free_page_report_status;
>      uint32_t num_pages;
>      uint32_t actual;
> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index af2b91f0b8..bb9207e7f4 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -360,6 +360,11 @@ void qemu_anon_ram_free(void *ptr, size_t size);
>  #else
>  #define QEMU_MADV_REMOVE QEMU_MADV_INVALID
>  #endif
> +#ifdef MADV_FREE
> +#define QEMU_MADV_FREE MADV_FREE
> +#else
> +#define QEMU_MADV_FREE QEMU_MADV_INVALID
> +#endif
>  
>  #elif defined(CONFIG_POSIX_MADVISE)
>  
> @@ -373,6 +378,7 @@ void qemu_anon_ram_free(void *ptr, size_t size);
>  #define QEMU_MADV_HUGEPAGE  QEMU_MADV_INVALID
>  #define QEMU_MADV_NOHUGEPAGE  QEMU_MADV_INVALID
>  #define QEMU_MADV_REMOVE QEMU_MADV_INVALID
> +#define QEMU_MADV_FREE QEMU_MADV_INVALID
>  
>  #else /* no-op */
>  
> @@ -386,6 +392,7 @@ void qemu_anon_ram_free(void *ptr, size_t size);
>  #define QEMU_MADV_HUGEPAGE  QEMU_MADV_INVALID
>  #define QEMU_MADV_NOHUGEPAGE  QEMU_MADV_INVALID
>  #define QEMU_MADV_REMOVE QEMU_MADV_INVALID
> +#define QEMU_MADV_FREE QEMU_MADV_INVALID
>  
>  #endif
>  
> diff --git a/include/standard-headers/linux/virtio_balloon.h b/include/standard-headers/linux/virtio_balloon.h
> index 9375ca2a70..f9e3e82562 100644
> --- a/include/standard-headers/linux/virtio_balloon.h
> +++ b/include/standard-headers/linux/virtio_balloon.h
> @@ -36,6 +36,7 @@
>  #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 */
> +#define VIRTIO_BALLOON_F_HINTING	5 /* Page hinting virtqueue */
>  
>  /* Size of a PFN in the balloon interface. */
>  #define VIRTIO_BALLOON_PFN_SHIFT 12
> -- 
> 2.21.0