On Thu, Jan 25, 2018 at 05:14:04PM +0800, Wei Wang wrote:
> This patch series is separated from the previous "Virtio-balloon
> Enhancement" series. The new feature, VIRTIO_BALLOON_F_FREE_PAGE_HINT,
> 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 from the source machine
> to the destination round by round. For the 1st round, all the VM's memory
> is transferred. From the 2nd round, only the pieces of memory that were
> written by the guest (after the 1st round) are transferred. One method
> that is popularly used by the hypervisor to track which part of memory is
> written is to write-protect all the guest memory.
>
> The second feature enables the optimization of the 1st round memory
> transfer - the hypervisor can skip the transfer of guest free pages in the
> 1st round. It is not concerned that the memory pages are used after they
> are given to the hypervisor as a hint of the free pages, because they will
> be tracked by the hypervisor and transferred in the next round if they are
> used and written.
Could you post performance numbers please?
> ChangeLog:
> v24->v25:
> - mm: change walk_free_mem_block to return 0 (instead of true) on
> completing the report, and return a non-zero value from the
> callabck, which stops the reporting.
> - virtio-balloon:
> - use enum instead of define for VIRTIO_BALLOON_VQ_INFLATE etc.
> - avoid __virtio_clear_bit when bailing out;
> - a new method to avoid reporting the some cmd id to host twice
> - destroy_workqueue can cancel free page work when the feature is
> negotiated;
> - fail probe when the free page vq size is less than 2.
> v23->v24:
> - change feature name VIRTIO_BALLOON_F_FREE_PAGE_VQ to
> VIRTIO_BALLOON_F_FREE_PAGE_HINT
> - kick when vq->num_free < half full, instead of "= half full"
> - replace BUG_ON with bailing out
> - check vb->balloon_wq in probe(), if null, bail out
> - add a new feature bit for page poisoning
> - solve the corner case that one cmd id being sent to host twice
> v22->v23:
> - change to kick the device when the vq is half-way full;
> - open-code batch_free_page_sg into add_one_sg;
> - change cmd_id from "uint32_t" to "__virtio32";
> - reserver one entry in the vq for teh driver to send cmd_id, instead
> of busywaiting for an available entry;
> - add "stop_update" check before queue_work for prudence purpose for
> now, will have a separate patch to discuss this flag check later;
> - init_vqs: change to put some variables on stack to have simpler
> implementation;
> - add destroy_workqueue(vb->balloon_wq);
>
> v21->v22:
> - add_one_sg: some code and comment re-arrangement
> - send_cmd_id: handle a cornercase
>
> For previous ChangeLog, please reference
> https://lwn.net/Articles/743660/
>
> Wei Wang (2):
> mm: support reporting free page blocks
> virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT
>
> drivers/virtio/virtio_balloon.c | 251
> ++--
> include/linux/mm.h | 6 +
> include/uapi/linux/virtio_balloon.h | 7 +
> mm/page_alloc.c | 96 ++
> 4 files changed, 324 insertions(+), 36 deletions(-)
>
> --
> 2.7.4
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