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Re: [Qemu-devel] [PATCH v11 7/7] virtio-balloon: VIRTIO_BALLOON_F_FREE_P
Dr. David Alan Gilbert
Re: [Qemu-devel] [PATCH v11 7/7] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT
Fri, 14 Dec 2018 09:56:47 +0000
* Wei Wang (address@hidden) wrote:
> On 12/13/2018 11:45 PM, Dr. David Alan Gilbert wrote:
> > * Wei Wang (address@hidden) wrote:
> > > The new feature enables the virtio-balloon device to receive hints of
> > > guest free pages from the free page vq.
> > >
> > > A notifier is registered to the migration precopy notifier chain. The
> > > notifier calls free_page_start after the migration thread syncs the dirty
> > > bitmap, so that the free page optimization starts to clear bits of free
> > > pages from the bitmap. It calls the free_page_stop before the migration
> > > thread syncs the bitmap, which is the end of the current round of ram
> > > save. The free_page_stop is also called to stop the optimization in the
> > > case when there is an error occurred in the process of ram saving.
> > >
> > > Note: balloon will report pages which were free at the time of this call.
> > > As the reporting happens asynchronously, dirty bit logging must be
> > > enabled before this free_page_start call is made. Guest reporting must be
> > > disabled before the migration dirty bitmap is synchronized.
> > >
> > > Signed-off-by: Wei Wang <address@hidden>
> > > CC: Michael S. Tsirkin <address@hidden>
> > > CC: Dr. David Alan Gilbert <address@hidden>
> > > CC: Juan Quintela <address@hidden>
> > > CC: Peter Xu <address@hidden>
> > I think I'm OK for this from the migration side, I'd appreciate
> > someone checking the virtio and aio bits.
> > I'm not too sure how it gets switched on and off - i.e. if we get a nice
> > new qemu on a new kernel, what happens when I try and migrate to the
> > same qemu on an older kernel without these hints?
> This feature doesn't rely on the host kernel. Those hints are reported from
> the guest kernel.
> So migration across different hosts wouldn't affect the use of this feature.
> Please correct me if I didn't get your point.
Ah OK, yes; now what about migrating from new->old qemu with a new
guest but old machine type?
Dr. David Alan Gilbert / address@hidden / Manchester, UK
Re: [Qemu-devel] [PATCH v11 0/7] virtio-balloon: free page hint support, Michael S. Tsirkin, 2018/12/14
- Re: [Qemu-devel] [PATCH v11 1/7] bitmap: fix bitmap_count_one, (continued)
- [Qemu-devel] [PATCH v11 3/7] migration: use bitmap_mutex in migration_bitmap_clear_dirty, Wei Wang, 2018/12/11
- [Qemu-devel] [PATCH v11 2/7] bitmap: bitmap_count_one_with_offset, Wei Wang, 2018/12/11
- [Qemu-devel] [PATCH v11 4/7] migration: API to clear bits of guest free pages from the dirty bitmap, Wei Wang, 2018/12/11
- [Qemu-devel] [PATCH v11 5/7] migration/ram.c: add a notifier chain for precopy, Wei Wang, 2018/12/11
- [Qemu-devel] [PATCH v11 6/7] migration/ram.c: add the free page optimization enable flag, Wei Wang, 2018/12/11
- [Qemu-devel] [PATCH v11 7/7] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT, Wei Wang, 2018/12/11