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SubjectRe: [QEMU Patch] virtio-baloon: Support for page hinting
On Wed, 10 Jul 2019 15:53:03 -0400
Nitesh Narayan Lal <nitesh@redhat.com> wrote:


$SUBJECT: s/baloon/balloon/

> Enables QEMU to perform madvise free on the memory range reported
> by the vm.

[No comments on the actual functionality; just some stuff I noticed.]

>
> Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>
> ---
> 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/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);

Indentation seems to be off here (also in other places; please double
check.)

> + 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.
> + */
> + 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);

I don't think you can add this unconditionally if you want to keep this
migratable. This should be done via a property (as for deflate-on-oom
and free-page-hint) so it can be turned off in compat machines.

>
> 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);

This should probably be conditional in the same way as the free page hint
queue (also see above).

>
> 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);

This object does not have any accessors; what purpose does it serve?

>
> object_property_add(obj, "guest-stats-polling-interval", "int",
> balloon_stats_get_poll_interval,

(...)

> 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

Please split off any update to these headers into a separate patch, so
that it can be replaced by a proper headers update when it is merged.

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