Re: [PATCH v22 2/3] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_VQ

From: Pankaj Gupta
Date: Wed Jan 17 2018 - 04:28:04 EST

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In reply to: Wei Wang: "Re: [PATCH v22 2/3] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_VQ"
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> On 01/17/2018 04:21 PM, Pankaj Gupta wrote:
> >> Negotiation of the VIRTIO_BALLOON_F_FREE_PAGE_VQ feature indicates the
> >> support of reporting hints of guest free pages to host via virtio-balloon.
> >>
> >> Host requests the guest to report free pages by sending a new cmd
> >> id to the guest via the free_page_report_cmd_id configuration register.
> >>
> >> When the guest starts to report, the first element added to the free page
> >> vq is the cmd id given by host. When the guest finishes the reporting
> >> of all the free pages, VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID is added
> >> to the vq to tell host that the reporting is done. Host may also requests
> >> the guest to stop the reporting in advance by sending the stop cmd id to
> >> the guest via the configuration register.
> >>
> >> Signed-off-by: Wei Wang <wei.w.wang@xxxxxxxxx>
> >> Signed-off-by: Liang Li <liang.z.li@xxxxxxxxx>
> >> Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
> >> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> >> ---
> >> drivers/virtio/virtio_balloon.c | 242
> >> +++++++++++++++++++++++++++++++-----
> >> include/uapi/linux/virtio_balloon.h | 4 +
> >> 2 files changed, 214 insertions(+), 32 deletions(-)
> >>
> >> diff --git a/drivers/virtio/virtio_balloon.c
> >> b/drivers/virtio/virtio_balloon.c
> >> index a1fb52c..b9561a5 100644
> >> --- a/drivers/virtio/virtio_balloon.c
> >> +++ b/drivers/virtio/virtio_balloon.c
> >> @@ -53,7 +53,12 @@ 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;
> >> @@ -63,6 +68,13 @@ struct virtio_balloon {
> >> spinlock_t stop_update_lock;
> >> bool stop_update;
> >>
> >> + /* Start to report free pages */
> >> + bool report_free_page;
> >> + /* Stores the cmd id given by host to start the free page reporting */
> >> + uint32_t start_cmd_id;
> >> + /* Stores STOP_ID as a sign to tell host that the reporting is done */
> >> + uint32_t stop_cmd_id;
> >> +
> >> /* Waiting for host to ack the pages we released. */
> >> wait_queue_head_t acked;
> >>
> >> @@ -281,6 +293,71 @@ static unsigned int update_balloon_stats(struct
> >> virtio_balloon *vb)
> >> return idx;
> >> }
> >>
> >> +static void add_one_sg(struct virtqueue *vq, unsigned long pfn, uint32_t
> >> len)
> >> +{
> >> + struct scatterlist sg;
> >> + unsigned int unused;
> >> + int err;
> >> +
> >> + sg_init_table(&sg, 1);
> >> + sg_set_page(&sg, pfn_to_page(pfn), len, 0);
> >> +
> >> + /* Detach all the used buffers from the vq */
> >> + while (virtqueue_get_buf(vq, &unused))
> >> + ;
> >> +
> >> + /*
> >> + * 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. We are adding one entry each time,
> >> + * which essentially results in no memory allocation, so the
> >> + * GFP_KERNEL flag below can be ignored.
> >> + */
> >> + if (vq->num_free) {
> >> + err = virtqueue_add_inbuf(vq, &sg, 1, vq, GFP_KERNEL);
> >> + /*
> >> + * This is expected to never fail, because there is always an
> >> + * entry available on the vq.
> >> + */
> >> + BUG_ON(err);
> >> + }
> >> +}
> >> +
> >> +static void batch_free_page_sg(struct virtqueue *vq,
> >> + unsigned long pfn,
> >> + uint32_t len)
> >> +{
> >> + add_one_sg(vq, pfn, len);
> >> +
> >> + /* Batch till the vq is full */
> >> + if (!vq->num_free)
> >> + virtqueue_kick(vq);
> >> +}
> >> +
> >> +static void send_cmd_id(struct virtqueue *vq, void *addr)
> >> +{
> >> + struct scatterlist sg;
> >> + unsigned int unused;
> >> + int err;
> >> +
> >> + sg_init_one(&sg, addr, sizeof(uint32_t));
> >> +
> >> + /*
> >> + * This handles the cornercase that the vq happens to be full when
> >> + * adding a cmd id. Rarely happen in practice.
> >> + */
> >> + while (!vq->num_free)
> >> + virtqueue_get_buf(vq, &unused);
> >> +
> >> + err = virtqueue_add_outbuf(vq, &sg, 1, vq, GFP_KERNEL);
> >> + /*
> >> + * This is expected to never fail, because there is always an
> >> + * entry available on the vq.
> >> + */
> >> + BUG_ON(err);
> >> + virtqueue_kick(vq);
> >> +}
> >> +
> >> /*
> >> * While most virtqueues communicate guest-initiated requests to the
> >> hypervisor,
> >> * the stats queue operates in reverse. The driver initializes the
> >> virtqueue
> >> @@ -316,17 +393,6 @@ static void stats_handle_request(struct
> >> virtio_balloon
> >> *vb)
> >> virtqueue_kick(vq);
> >> }
> >>
> >> -static void virtballoon_changed(struct virtio_device *vdev)
> >> -{
> >> - struct virtio_balloon *vb = vdev->priv;
> >> - unsigned long flags;
> >> -
> >> - spin_lock_irqsave(&vb->stop_update_lock, flags);
> >> - if (!vb->stop_update)
> >> - queue_work(system_freezable_wq, &vb->update_balloon_size_work);
> >> - spin_unlock_irqrestore(&vb->stop_update_lock, flags);
> >> -}
> >> -
> >> static inline s64 towards_target(struct virtio_balloon *vb)
> >> {
> >> s64 target;
> >> @@ -343,6 +409,36 @@ static inline s64 towards_target(struct
> >> virtio_balloon
> >> *vb)
> >> return target - vb->num_pages;
> >> }
> >>
> >> +static void virtballoon_changed(struct virtio_device *vdev)
> >> +{
> >> + struct virtio_balloon *vb = vdev->priv;
> >> + unsigned long flags;
> >> + __u32 cmd_id;
> >> + s64 diff = towards_target(vb);
> >> +
> >> + if (diff) {
> >> + spin_lock_irqsave(&vb->stop_update_lock, flags);
> >> + if (!vb->stop_update)
> >> + queue_work(system_freezable_wq,
> >> + &vb->update_balloon_size_work);
> >> + spin_unlock_irqrestore(&vb->stop_update_lock, flags);
> >> + }
> >> +
> >> + virtio_cread(vb->vdev, struct virtio_balloon_config,
> >> + free_page_report_cmd_id, &cmd_id);
> >> + if (cmd_id == VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID) {
> >> + WRITE_ONCE(vb->report_free_page, false);
> >> + } else if (cmd_id != vb->start_cmd_id) {
> >> + /*
> >> + * Host requests to start the reporting by sending a new cmd
> >> + * id.
> >> + */
> >> + WRITE_ONCE(vb->report_free_page, true);
> >> + vb->start_cmd_id = cmd_id;
> >> + queue_work(vb->balloon_wq, &vb->report_free_page_work);
> >> + }
> >> +}
> >> +
> >> static void update_balloon_size(struct virtio_balloon *vb)
> >> {
> >> u32 actual = vb->num_pages;
> >> @@ -417,40 +513,113 @@ static void update_balloon_size_func(struct
> >> work_struct *work)
> >>
> >> static int init_vqs(struct virtio_balloon *vb)
> >> {
> >> - 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 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++;
> >> + }
> >>
> >> - /*
> >> - * We expect two virtqueues: inflate and deflate, and
> >> - * optionally stat.
> >> - */
> >> - 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 (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;
> >
> > We can assign err=0 and remove above duplicate code?
> >
>
> Where do you want to assign err=0? Could you show it using code?

o.k you have initialize "err = -ENOMEM;"

Remove these four lines.

- kfree(names);
- kfree(callbacks);
- kfree(vqs);
- return 0;

+ err = 0; // if executed without any error

Below code is already there, so for error, err is already 'ENOMEM'
and a jump to any label.

+
+err_find:
+ kfree(names);
+err_names:
+ kfree(callbacks);
+err_callback:
+ kfree(vqs);
> +err_vq:
> + return err;
> +}

Thanks,
Pankaj

>
>
> Best,
> Wei
>
>
>

Next message: Peter Rosin: "Re: [REGRESSION] linux-next panics when trying to mount root"
Previous message: Baoquan He: "Re: [RESEND PATCH 1/3] x86/apic: Set up through LAPIC on boot CPU's LINT0 if ioapic is disabled"
In reply to: Wei Wang: "Re: [PATCH v22 2/3] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_VQ"
Next in thread: Wei Wang: "Re: [PATCH v22 2/3] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_VQ"
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