> The other thing to keep in mind is that the poison value only really > comes into play with hinting/reporting. In the case of the standard > balloon the pages are considered allocated from the guest's
Currently just as free page hinting IMHO. They are temporarily considered allocated. > perspective until the balloon is deflated. Then any poison/init will > occur over again anyway so I don't think the standard balloon should > really care. I think we should make this consistent. And as we discuss below, this allows for a nice optimization in the guest even for ordinary inflation/deflation (no need to zero out/poison again when giving the pages back to the buddy). > > For hinting it somewhat depends. Currently the implementation is > inflating a balloon so having poisoning or init_on_free means it is > written to immediately after it is freed so it defeats the purpose of > the hinting. However that is a Linux implementation issue, not Yeah, and as we discuss below, we can optimize that later in Linux. It's sub-optimal, I agree. > necessarily an issue with the QEMU implementation. As such may be I > should fix that in the Linux driver since that has been ignored in > QEMU up until now anyway. The more interesting bit is what should the > behavior be from the hypervisor when a page is marked as being hinted. > I think right now the behavior is to just not migrate the page. I > wonder though if we shouldn't instead just consider the page a zero > page, and then maybe modify the zero page behavior for the case where > we know page poisoning is enabled. I consider that maybe future work. Let's keep it simple for now (iow, try to get page poisoning handling right first). The optimize the guest handling on balloon deflation / end of free page hinting. [...] >> I can totally understand if Alex would want to stop working on >> VIRTIO_BALLOON_F_PAGE_POISON at this point and only fix the guest to not >> enable free page reporting in case we don't have >> VIRTIO_BALLOON_F_PAGE_POISON (unless that's already done), lol. :) > > I already have a patch for that. > > The bigger issue is how to deal with the PAGE_POISON being enabled > with FREE_PAGE_HINTING. The legacy code at this point is just broken > and is plowing through with FREE_PAGE_HINTING while it is enabled. > That is safe for now because it is using a balloon, the side effect is > that it is going to defer migration. If it switches to a page > reporting type setup at some point in the future we would need to make > sure something is written to the other end to identify the poison/zero > pages. I think we don't have to worry about that for now. Might be sub-optimal, but then, I don't think actual page poisoning isn't all that frequently used in production setups. -- Thanks, David / dhildenb --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscr...@lists.oasis-open.org For additional commands, e-mail: virtio-dev-h...@lists.oasis-open.org
