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SubjectRe: [PATCH v17 6/6] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_VQ
Ping for comments, thanks.

On 11/03/2017 04:13 PM, Wei Wang wrote:
> Negotiation of the VIRTIO_BALLOON_F_FREE_PAGE_VQ feature indicates the
> support of reporting hints of guest free pages to the host via
> virtio-balloon. The host requests the guest to report the free pages by
> sending commands via the virtio-balloon configuration registers.
>
> When the guest starts to report, the first element added to the free page
> vq is a sequence id of the start reporting command. The id is given by
> the host, and it indicates whether the following free pages correspond
> to the command. For example, the host may stop the report and start again
> with a new command id. The obsolete pages for the previous start command
> can be detected by the id dismatching on the host. The id is added to the
> vq using an output buffer, and the free pages are added to the vq using
> input buffer.
>
> Here are some explainations about the added configuration registers:
> - host2guest_cmd: a register used by the host to send commands to the
> guest.
> - guest2host_cmd: written by the guest to ACK to the host about the
> commands that have been received. The host will clear the corresponding
> bits on the host2guest_cmd register. The guest also uses this register
> to send commands to the host (e.g. when finish free page reporting).
> - free_page_cmd_id: the sequence id of the free page report command
> given by the host.
>
> Signed-off-by: Wei Wang <wei.w.wang@intel.com>
> Signed-off-by: Liang Li <liang.z.li@intel.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Michal Hocko <mhocko@kernel.org>
> ---
> drivers/virtio/virtio_balloon.c | 234 ++++++++++++++++++++++++++++++++----
> include/uapi/linux/virtio_balloon.h | 11 ++
> 2 files changed, 223 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index b31fc25..4087f04 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -55,7 +55,12 @@ static struct vfsmount *balloon_mnt;
>
> struct virtio_balloon {
> struct virtio_device *vdev;
> - struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
> + struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *free_page_vq;
> +
> + /* Balloon's own wq for cpu-intensive work items */
> + struct workqueue_struct *balloon_wq;
> + /* The free page reporting work item submitted to the balloon wq */
> + struct work_struct report_free_page_work;
>
> /* The balloon servicing is delegated to a freezable workqueue. */
> struct work_struct update_balloon_stats_work;
> @@ -65,6 +70,10 @@ struct virtio_balloon {
> spinlock_t stop_update_lock;
> bool stop_update;
>
> + /* Stop reporting free pages */
> + bool report_free_page_stop;
> + uint32_t free_page_cmd_id;
> +
> /* Waiting for host to ack the pages we released. */
> wait_queue_head_t acked;
>
> @@ -191,6 +200,30 @@ static void send_balloon_page_sg(struct virtio_balloon *vb,
> kick_and_wait(vq, vb->acked);
> }
>
> +static void send_free_page_sg(struct virtqueue *vq, void *addr, uint32_t size)
> +{
> + int err = 0;
> + unsigned int len;
> +
> + /* Detach all the used buffers from the vq */
> + while (virtqueue_get_buf(vq, &len))
> + ;
> +
> + /*
> + * Since this is an optimization feature, losing a couple of free
> + * pages to report isn't important. We simply resturn without adding
> + * the page if the vq is full.
> + */
> + if (vq->num_free) {
> + err = add_one_sg(vq, addr, size);
> + BUG_ON(err);
> + }
> +
> + /* Batch till the vq is full */
> + if (!vq->num_free)
> + virtqueue_kick(vq);
> +}
> +
> /*
> * Send balloon pages in sgs to host. The balloon pages are recorded in the
> * page xbitmap. Each bit in the bitmap corresponds to a page of PAGE_SIZE.
> @@ -495,9 +528,8 @@ static void stats_handle_request(struct virtio_balloon *vb)
> virtqueue_kick(vq);
> }
>
> -static void virtballoon_changed(struct virtio_device *vdev)
> +static void virtballoon_cmd_balloon_memory(struct virtio_balloon *vb)
> {
> - struct virtio_balloon *vb = vdev->priv;
> unsigned long flags;
>
> spin_lock_irqsave(&vb->stop_update_lock, flags);
> @@ -506,6 +538,50 @@ static void virtballoon_changed(struct virtio_device *vdev)
> spin_unlock_irqrestore(&vb->stop_update_lock, flags);
> }
>
> +static void virtballoon_cmd_report_free_page_start(struct virtio_balloon *vb)
> +{
> + unsigned long flags;
> +
> + vb->report_free_page_stop = false;
> + spin_lock_irqsave(&vb->stop_update_lock, flags);
> + if (!vb->stop_update)
> + queue_work(vb->balloon_wq, &vb->report_free_page_work);
> + spin_unlock_irqrestore(&vb->stop_update_lock, flags);
> +}
> +
> +static void virtballoon_changed(struct virtio_device *vdev)
> +{
> + struct virtio_balloon *vb = vdev->priv;
> + u32 host2guest_cmd, guest2host_cmd = 0;
> +
> + if (!virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_VQ)) {
> + virtballoon_cmd_balloon_memory(vb);
> + return;
> + }
> +
> + virtio_cread(vb->vdev, struct virtio_balloon_config, host2guest_cmd,
> + &host2guest_cmd);
> +
> + if (host2guest_cmd & VIRTIO_BALLOON_CMD_BALLOON_MEMORY) {
> + virtballoon_cmd_balloon_memory(vb);
> + guest2host_cmd |= VIRTIO_BALLOON_CMD_BALLOON_MEMORY;
> + }
> +
> + if (host2guest_cmd & VIRTIO_BALLOON_CMD_REPORT_FREE_PAGE_START) {
> + virtballoon_cmd_report_free_page_start(vb);
> + guest2host_cmd |= VIRTIO_BALLOON_CMD_REPORT_FREE_PAGE_START;
> + }
> +
> + if (host2guest_cmd & VIRTIO_BALLOON_CMD_REPORT_FREE_PAGE_STOP) {
> + vb->report_free_page_stop = true;
> + guest2host_cmd |= VIRTIO_BALLOON_CMD_REPORT_FREE_PAGE_STOP;
> + }
> +
> + /* Ack to the host about the commands that have been received */
> + virtio_cwrite(vb->vdev, struct virtio_balloon_config, guest2host_cmd,
> + &guest2host_cmd);
> +}
> +
> static inline s64 towards_target(struct virtio_balloon *vb)
> {
> s64 target;
> @@ -597,42 +673,147 @@ static void update_balloon_size_func(struct work_struct *work)
> queue_work(system_freezable_wq, work);
> }
>
> -static int init_vqs(struct virtio_balloon *vb)
> +static bool virtio_balloon_send_free_pages(void *opaque, unsigned long pfn,
> + unsigned long nr_pages)
> {
> - struct virtqueue *vqs[3];
> - vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
> - static const char * const names[] = { "inflate", "deflate", "stats" };
> - int err, nvqs;
> + struct virtio_balloon *vb = (struct virtio_balloon *)opaque;
> + void *addr = (void *)pfn_to_kaddr(pfn);
> + uint32_t len = nr_pages << PAGE_SHIFT;
> +
> + if (vb->report_free_page_stop)
> + return false;
> +
> + send_free_page_sg(vb->free_page_vq, addr, len);
>
> + return true;
> +}
> +
> +static void report_free_page_end(struct virtio_balloon *vb)
> +{
> + u32 cmd = VIRTIO_BALLOON_CMD_REPORT_FREE_PAGE_STOP;
> /*
> - * We expect two virtqueues: inflate and deflate, and
> - * optionally stat.
> + * The host may have already requested to stop the reporting before we
> + * finish, so no need to notify the host in this case.
> */
> - nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
> - err = virtio_find_vqs(vb->vdev, nvqs, vqs, callbacks, names, NULL);
> + if (vb->report_free_page_stop)
> + return;
> + vb->report_free_page_stop = true;
> +
> + virtio_cwrite(vb->vdev, struct virtio_balloon_config, guest2host_cmd,
> + &cmd);
> +}
> +
> +static void report_free_page_cmd_id(struct virtio_balloon *vb)
> +{
> + struct scatterlist sg;
> + int err;
> +
> + virtio_cread(vb->vdev, struct virtio_balloon_config, free_page_cmd_id,
> + &vb->free_page_cmd_id);
> + sg_init_one(&sg, &vb->free_page_cmd_id, sizeof(uint32_t));
> + err = virtqueue_add_outbuf(vb->free_page_vq, &sg, 1,
> + &vb->free_page_cmd_id, GFP_KERNEL);
> + BUG_ON(err);
> +}
> +
> +static void report_free_page(struct work_struct *work)
> +{
> + struct virtio_balloon *vb;
> +
> + vb = container_of(work, struct virtio_balloon, report_free_page_work);
> + report_free_page_cmd_id(vb);
> + walk_free_mem_block(vb, 0, &virtio_balloon_send_free_pages);
> + /*
> + * The last few free page blocks that were added may not reach the
> + * batch size, but need a kick to notify the device to handle them.
> + */
> + virtqueue_kick(vb->free_page_vq);
> + report_free_page_end(vb);
> +}
> +
> +static int init_vqs(struct virtio_balloon *vb)
> +{
> + struct virtqueue **vqs;
> + vq_callback_t **callbacks;
> + const char **names;
> + struct scatterlist sg;
> + int i, nvqs, err = -ENOMEM;
> +
> + /* Inflateq and deflateq are used unconditionally */
> + nvqs = 2;
> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ))
> + nvqs++;
> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_VQ))
> + nvqs++;
> +
> + /* Allocate space for find_vqs parameters */
> + vqs = kcalloc(nvqs, sizeof(*vqs), GFP_KERNEL);
> + if (!vqs)
> + goto err_vq;
> + callbacks = kmalloc_array(nvqs, sizeof(*callbacks), GFP_KERNEL);
> + if (!callbacks)
> + goto err_callback;
> + names = kmalloc_array(nvqs, sizeof(*names), GFP_KERNEL);
> + if (!names)
> + goto err_names;
> +
> + callbacks[0] = balloon_ack;
> + names[0] = "inflate";
> + callbacks[1] = balloon_ack;
> + names[1] = "deflate";
> +
> + i = 2;
> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
> + callbacks[i] = stats_request;
> + names[i] = "stats";
> + i++;
> + }
> +
> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_VQ)) {
> + callbacks[i] = NULL;
> + names[i] = "free_page_vq";
> + }
> +
> + err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks, names,
> + NULL, NULL);
> if (err)
> - return err;
> + goto err_find;
>
> vb->inflate_vq = vqs[0];
> vb->deflate_vq = vqs[1];
> + i = 2;
> if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
> - struct scatterlist sg;
> - unsigned int num_stats;
> - vb->stats_vq = vqs[2];
> -
> + vb->stats_vq = vqs[i++];
> /*
> * Prime this virtqueue with one buffer so the hypervisor can
> * use it to signal us later (it can't be broken yet!).
> */
> - num_stats = update_balloon_stats(vb);
> -
> - sg_init_one(&sg, vb->stats, sizeof(vb->stats[0]) * num_stats);
> + sg_init_one(&sg, vb->stats, sizeof(vb->stats));
> if (virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb, GFP_KERNEL)
> - < 0)
> - BUG();
> + < 0) {
> + dev_warn(&vb->vdev->dev, "%s: add stat_vq failed\n",
> + __func__);
> + goto err_find;
> + }
> virtqueue_kick(vb->stats_vq);
> }
> +
> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_VQ))
> + vb->free_page_vq = vqs[i];
> +
> + kfree(names);
> + kfree(callbacks);
> + kfree(vqs);
> return 0;
> +
> +err_find:
> + kfree(names);
> +err_names:
> + kfree(callbacks);
> +err_callback:
> + kfree(vqs);
> +err_vq:
> + return err;
> }
>
> #ifdef CONFIG_BALLOON_COMPACTION
> @@ -761,6 +942,13 @@ static int virtballoon_probe(struct virtio_device *vdev)
> if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_SG))
> xb_init(&vb->page_xb);
>
> + if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_VQ)) {
> + vb->balloon_wq = alloc_workqueue("balloon-wq",
> + WQ_FREEZABLE | WQ_CPU_INTENSIVE, 0);
> + INIT_WORK(&vb->report_free_page_work, report_free_page);
> + vb->report_free_page_stop = true;
> + }
> +
> vb->nb.notifier_call = virtballoon_oom_notify;
> vb->nb.priority = VIRTBALLOON_OOM_NOTIFY_PRIORITY;
> err = register_oom_notifier(&vb->nb);
> @@ -825,6 +1013,7 @@ static void virtballoon_remove(struct virtio_device *vdev)
> spin_unlock_irq(&vb->stop_update_lock);
> cancel_work_sync(&vb->update_balloon_size_work);
> cancel_work_sync(&vb->update_balloon_stats_work);
> + cancel_work_sync(&vb->report_free_page_work);
>
> remove_common(vb);
> #ifdef CONFIG_BALLOON_COMPACTION
> @@ -878,6 +1067,7 @@ static unsigned int features[] = {
> VIRTIO_BALLOON_F_STATS_VQ,
> VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
> VIRTIO_BALLOON_F_SG,
> + VIRTIO_BALLOON_F_FREE_PAGE_VQ,
> };
>
> static struct virtio_driver virtio_balloon_driver = {
> diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
> index 37780a7..b758484 100644
> --- a/include/uapi/linux/virtio_balloon.h
> +++ b/include/uapi/linux/virtio_balloon.h
> @@ -35,15 +35,26 @@
> #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_SG 3 /* Use sg instead of PFN lists */
> +#define VIRTIO_BALLOON_F_FREE_PAGE_VQ 4 /* VQ to report free pages */
>
> /* Size of a PFN in the balloon interface. */
> #define VIRTIO_BALLOON_PFN_SHIFT 12
>
> +#define VIRTIO_BALLOON_CMD_BALLOON_MEMORY (1 << 0)
> +#define VIRTIO_BALLOON_CMD_REPORT_FREE_PAGE_START (1 << 1)
> +#define VIRTIO_BALLOON_CMD_REPORT_FREE_PAGE_STOP (1 << 2)
> +
> struct virtio_balloon_config {
> /* Number of pages host wants Guest to give up. */
> __u32 num_pages;
> /* Number of pages we've actually got in balloon. */
> __u32 actual;
> + /* Host-to-guest command, readonly by guest */
> + __u32 host2guest_cmd;
> + /* Sequence id of the free_page report command, readonly by guest */
> + __u32 free_page_cmd_id;
> + /* Guest-to-host command */
> + __u32 guest2host_cmd;
> };
>
> #define VIRTIO_BALLOON_S_SWAP_IN 0 /* Amount of memory swapped in */

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