search for: free_page_hint

...gnal. That is not really possible because it might >> take an infinite amount of time. >> >> 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. Signalled via using > the buffer. But maybe that's too far in the meaning from > VIRTIO_BALLOON_F_MUST_TELL_HOST and we need a separa...

...gnal. That is not really possible because it might >> take an infinite amount of time. >> >> 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. Signalled via using > the buffer. But maybe that's too far in the meaning from > VIRTIO_BALLOON_F_MUST_TELL_HOST and we need a separa...

...possible because it might > >> take an infinite amount of time. > >> > >> 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. Signalled via using > > the buffer. But maybe that's too far in the meaning from > > VIRTIO_BALLOON_F_MUST_TELL_...

...his is to cover the case where somebody is running the code prior to my QEMU changes where the page poison feature wasn't being enabled. > We don't know what hypervisor uses the hints for. I agree, but at the same time the way the feature was originally coded it was only checked if the FREE_PAGE_HINT feature was enabled. The assumption there is that if we have page poison data and want to use hints we need to report it. In my mind if we ever want to switch over to the page reporting style setup for page hinting in the future we will need to have it behave in a sane manner. So disabling it if we...

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

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

...;> >>>> I think the shrinker makes sense for free page hinting feature >>>> (everything on free_page_list). >>>> >>>> So instead of only reverting, I think we should split it up and always >>>> register the shrinker for VIRTIO_BALLOON_F_FREE_PAGE_HINT and the OOM >>>> notifier (as before) for VIRTIO_BALLOON_F_MUST_TELL_HOST. >> >> s/VIRTIO_BALLOON_F_MUST_TELL_HOST/VIRTIO_BALLOON_F_DEFLATE_ON_OOM/ >> >> :) > > Well VIRTIO_BALLOON_F_MUST_TELL_HOST is also broken by shrinker > with VIRTIO_BALLOON_F_FREE...

...;> >>>> I think the shrinker makes sense for free page hinting feature >>>> (everything on free_page_list). >>>> >>>> So instead of only reverting, I think we should split it up and always >>>> register the shrinker for VIRTIO_BALLOON_F_FREE_PAGE_HINT and the OOM >>>> notifier (as before) for VIRTIO_BALLOON_F_MUST_TELL_HOST. >> >> s/VIRTIO_BALLOON_F_MUST_TELL_HOST/VIRTIO_BALLOON_F_DEFLATE_ON_OOM/ >> >> :) > > Well VIRTIO_BALLOON_F_MUST_TELL_HOST is also broken by shrinker > with VIRTIO_BALLOON_F_FREE...

...ot obey MUST_TELL_HOST under OOM. But that unfortunately is a guest not a host bug, so this hack does not seem useful. > > We don't know what hypervisor uses the hints for. > > I agree, but at the same time the way the feature was originally coded > it was only checked if the FREE_PAGE_HINT feature was enabled. The > assumption there is that if we have page poison data and want to use > hints we need to report it. In my mind if we ever want to switch over > to the page reporting style setup for page hinting in the future we > will need to have it behave in a sane manner. S...

...t;drop everything". We really want an API that says "drop everything that hasn't been accessed in the last 5 minutes". This would eliminate the need for the balloon to cause memory pressure at all which avoids the inefficiency in question. Furthermore, this pairs nicely with the FREE_PAGE_HINT feature. On Mon, Feb 3, 2020 at 9:04 AM Michael S. Tsirkin <mst at redhat.com> wrote: > On Mon, Feb 03, 2020 at 05:34:20PM +0100, David Hildenbrand wrote: > > On 03.02.20 17:18, Alexander Duyck wrote: > > > On Mon, 2020-02-03 at 08:11 -0500, Michael S. Tsirkin wrote: >...

...t;drop everything". We really want an API that says "drop everything that hasn't been accessed in the last 5 minutes". This would eliminate the need for the balloon to cause memory pressure at all which avoids the inefficiency in question. Furthermore, this pairs nicely with the FREE_PAGE_HINT feature. On Mon, Feb 3, 2020 at 9:04 AM Michael S. Tsirkin <mst at redhat.com> wrote: > On Mon, Feb 03, 2020 at 05:34:20PM +0100, David Hildenbrand wrote: > > On 03.02.20 17:18, Alexander Duyck wrote: > > > On Mon, 2020-02-03 at 08:11 -0500, Michael S. Tsirkin wrote: >...

...at says "drop everything that > > hasn't been accessed in the last 5 minutes". > > > > This would eliminate the need for the balloon to cause memory pressure > > at all which avoids the inefficiency in question. Furthermore, this > > pairs nicely with the FREE_PAGE_HINT feature. > > Something similar was brought up in the discussion we had about this in my > patch set. The problem is, by trying to use a value like "5 minutes" it > implies that we are going to need to track some extra state somewhere to > determine that value. > > An...

...(IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY) || - !page_poisoning_enabled())) + !page_poisoning_enabled())) { __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON); + } else if (!virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) { + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT); + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_REPORTING); + } __virtio_clear_bit(vdev, VIRTIO_F_IOMMU_PLATFORM); return 0;

...(IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY) || - !page_poisoning_enabled())) + !page_poisoning_enabled())) { __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON); + } else if (!virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) { + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT); + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_REPORTING); + } __virtio_clear_bit(vdev, VIRTIO_F_IOMMU_PLATFORM); return 0;

...;> free memory is depleted and we're inflating into page cache. >> >> So given this looks like a regression, maybe we should revert the >> patch in question 71994620bb25 ("virtio_balloon: replace oom notifier with shrinker") >> Besides, with VIRTIO_BALLOON_F_FREE_PAGE_HINT >> shrinker also ignores VIRTIO_BALLOON_F_MUST_TELL_HOST which isn't nice >> at all. >> >> So it looks like all this rework introduced more issues than it >> addressed ... >> >> I also CC Alex Duyck for an opinion on this. >> Alex, what do you use...

...;> free memory is depleted and we're inflating into page cache. >> >> So given this looks like a regression, maybe we should revert the >> patch in question 71994620bb25 ("virtio_balloon: replace oom notifier with shrinker") >> Besides, with VIRTIO_BALLOON_F_FREE_PAGE_HINT >> shrinker also ignores VIRTIO_BALLOON_F_MUST_TELL_HOST which isn't nice >> at all. >> >> So it looks like all this rework introduced more issues than it >> addressed ... >> >> I also CC Alex Duyck for an opinion on this. >> Alex, what do you use...

...L_HOST 0 /* Tell before reclaiming pages */ > #define VIRTIO_BALLOON_F_STATS_VQ 1 /* Memory Stats virtqueue */ > #define VIRTIO_BALLOON_F_DEFLATE_ON_OOM 2 /* Deflate balloon on OOM */ > +#define VIRTIO_BALLOON_F_FREE_PAGE_VQ 3 /* VQ to report free pages */ I'd call it something like FREE_PAGE_HINT > > /* Size of a PFN in the balloon interface. */ > #define VIRTIO_BALLOON_PFN_SHIFT 12 > > +#define VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID 0 > struct virtio_balloon_config { > /* Number of pages host wants Guest to give up. */ > __u32 num_pages; > /* Numb...

...L_HOST 0 /* Tell before reclaiming pages */ > #define VIRTIO_BALLOON_F_STATS_VQ 1 /* Memory Stats virtqueue */ > #define VIRTIO_BALLOON_F_DEFLATE_ON_OOM 2 /* Deflate balloon on OOM */ > +#define VIRTIO_BALLOON_F_FREE_PAGE_VQ 3 /* VQ to report free pages */ I'd call it something like FREE_PAGE_HINT > > /* Size of a PFN in the balloon interface. */ > #define VIRTIO_BALLOON_PFN_SHIFT 12 > > +#define VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID 0 > struct virtio_balloon_config { > /* Number of pages host wants Guest to give up. */ > __u32 num_pages; > /* Numb...

This patch series is separated from the previous "Virtio-balloon Enhancement" series. The new feature, VIRTIO_BALLOON_F_FREE_PAGE_VQ, implemented by this series enables the virtio-balloon driver to report hints of guest free pages to the host. It can be used to accelerate live migration of VMs. Here is an introduction of this usage: Live migration needs to transfer the VM's memory