On Wed, Feb 05, 2020 at 06:52:34AM +0000, Wang, Wei W wrote: > On Wednesday, February 5, 2020 12:50 AM, Michael S. Tsirkin wrote: > > > Michael, any clue on which event we have to wait with > > > VIRTIO_BALLOON_F_MUST_TELL_HOST? IMHO, I don't think > > > VIRTIO_BALLOON_F_MUST_TELL_HOST applies to > > > VIRTIO_BALLOON_F_FREE_PAGE_HINT and we'd better document that. It > > introduces complexity with no clear benefit. > > > > I meant that we must wait for host to see the hint. > > Why? > > Best, > Wei Well if we did the hint would be reliable, allowing host to immediately drop any pages it gets in the hint. 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 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, so we could have used it to mean "hints must wait for host to use buffers". I'm afraid it's already a wasted opportunity at this point, reusing it isn't worth the compatibility headaches. -- MST
