On Wednesday, February 5, 2020 3:05 PM, Michael S. Tsirkin wrote:

Well if we did the hint would be reliable, allowing host to immediately drop
any pages it gets in the hint. 

"drop", you mean host to unmap the page from guest? I think that's not allowed for hints.

Originally I wanted to speed up hinting by never
waiting for host, but that does not seem to be what was
implemented: the only place we don't wait is the shrinker

Didn't get this one. For FREE_PAGE_HINT, the hints are always sent to host without
an ack from host about whether it has read the hint or not. (please see get_free_page_and_send)

and it seems a
waste that we introduced complexity to host without getting any real
benefit out of it.

VIRTIO_BALLOON_F_MUST_TELL_HOST doesn't really apply to hinting right
now, 

There is no need I think, as host isn't allowed to use or unmap the hint page.

Best,
Wei