Re: [virtio-dev] Re: [PATCH] virtio-balloon: Disable free page hinting/reporting if page poison is disabled

[David Hildenbrand <david@redhat.com>]

On 17.04.20 12:19, Michael S. Tsirkin wrote:
> On Fri, Apr 17, 2020 at 12:09:38PM +0200, David Hildenbrand wrote:
>>  > What do you call "hinting ends" though? The fact we put
>>> a page in the VQ is not a guarantee that it's been consumed
>>> by the hypervisor.
>>>
>>
>> I'd say hinting ends once the hypervisor sets FREE_PAGE_REPORT_S_DONE.
> 
> Can't find that one anywhere. what did I miss?

Sorry, the QEMU implementation is confusing. FREE_PAGE_REPORT_S_DONE is
translated to VIRTIO_BALLOON_CMD_ID_DONE

QEMU:

hw/virtio/virtio-balloon.c:virtio_balloon_free_page_report_notify()
-> virtio_balloon_free_page_done(dev)
-> s->free_page_report_status = FREE_PAGE_REPORT_S_DONE;
   virtio_notify_config(vdev);

When the guest reads the config
hw/virtio/virtio-balloon.c:virtio_balloon_get_config()
-> if (dev->free_page_report_status == FREE_PAGE_REPORT_S_DONE)
-> config.free_page_report_cmd_id = ... VIRTIO_BALLOON_CMD_ID_DONE


Linux:

drivers/virtio/virtio_balloon.c:report_free_page_func()
-> if (cmd_id_received == VIRTIO_BALLOON_CMD_ID_DONE) {
-> return_free_pages_to_mm()


So it's VIRTIO_BALLOON_CMD_ID_DONE.


-- 
Thanks,

David / dhildenb