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

From: Nitesh Narayan Lal
Date: Thu Jul 11 2019 - 07:13:43 EST


On 7/11/19 4:49 AM, Cornelia Huck wrote:
> On Wed, 10 Jul 2019 15:53:03 -0400
> Nitesh Narayan Lal <nitesh@xxxxxxxxxx> 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@xxxxxxxxxx>
>> ---
>> 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.)
Thanks, I will check it.
>
>> + 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.
I see, I will take a look at it.
>
>>
>> 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).
Makes sense. Thanks.
>
>>
>> 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?
I think its not required. I will correct this.
>
>>
>> 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.
I will do that.
--
Thanks
Nitesh