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

[Nitesh Narayan Lal <nitesh@redhat.com>]

On 7/11/19 4:49 AM, Cornelia Huck wrote:
> 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.)
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