Re: [PATCH v34 2/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT
From: Michael S. Tsirkin
Date: Mon Jun 25 2018 - 21:37:12 EST
On Mon, Jun 25, 2018 at 08:05:10PM +0800, Wei Wang wrote:
> Negotiation of the VIRTIO_BALLOON_F_FREE_PAGE_HINT feature indicates the
> support of reporting hints of guest free pages to host via virtio-balloon.
>
> Host requests the guest to report free page hints by sending a new cmd id
> to the guest via the free_page_report_cmd_id configuration register.
>
> As the first step here, virtio-balloon only reports free page hints from
> the max order (i.e. 10) free page list to host. This has generated similar
> good results as reporting all free page hints during our tests.
>
> When the guest starts to report, it first sends a start cmd to host via
> the free page vq, which acks to host the cmd id received, and tells it the
> hint size (e.g. 4MB each on x86). When the guest finishes the reporting,
> a stop cmd is sent to host via the vq.
>
> TODO:
> - support reporting free page hints from smaller order free page lists
> when there is a need/request from users.
>
> 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>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
> drivers/virtio/virtio_balloon.c | 347 ++++++++++++++++++++++++++++++++----
> include/uapi/linux/virtio_balloon.h | 11 ++
> 2 files changed, 322 insertions(+), 36 deletions(-)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 6b237e3..d05f0ba 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -43,6 +43,11 @@
> #define OOM_VBALLOON_DEFAULT_PAGES 256
> #define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80
>
> +/* The order used to allocate an array to load free page hints */
> +#define ARRAY_ALLOC_ORDER (MAX_ORDER - 1)
> +/* The size of an array in bytes */
> +#define ARRAY_ALLOC_SIZE ((1 << ARRAY_ALLOC_ORDER) << PAGE_SHIFT)
> +
Pls prefix macros so we can figure out they are local ones.
> static int oom_pages = OOM_VBALLOON_DEFAULT_PAGES;
> module_param(oom_pages, int, S_IRUSR | S_IWUSR);
> MODULE_PARM_DESC(oom_pages, "pages to free on OOM");
> @@ -51,9 +56,22 @@ MODULE_PARM_DESC(oom_pages, "pages to free on OOM");
> static struct vfsmount *balloon_mnt;
> #endif
>
> +enum virtio_balloon_vq {
> + VIRTIO_BALLOON_VQ_INFLATE,
> + VIRTIO_BALLOON_VQ_DEFLATE,
> + VIRTIO_BALLOON_VQ_STATS,
> + VIRTIO_BALLOON_VQ_FREE_PAGE,
> + VIRTIO_BALLOON_VQ_MAX
> +};
> +
> 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 +81,15 @@ struct virtio_balloon {
> spinlock_t stop_update_lock;
> bool stop_update;
>
> + /* Command buffers to start and stop the reporting of hints to host */
> + struct virtio_balloon_free_page_hints_cmd cmd_start;
> + struct virtio_balloon_free_page_hints_cmd cmd_stop;
> +
> + /* The cmd id received from host */
> + uint32_t cmd_id_received;
> + /* The cmd id that is actively in use */
> + uint32_t cmd_id_active;
> +
> /* Waiting for host to ack the pages we released. */
> wait_queue_head_t acked;
>
You want u32 types.
> @@ -326,17 +353,6 @@ 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;
> @@ -353,6 +369,35 @@ 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;
> + 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);
> + }
> +
> + if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
> + virtio_cread(vdev, struct virtio_balloon_config,
> + free_page_report_cmd_id, &vb->cmd_id_received);
> + if (vb->cmd_id_received !=
> + VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID &&
> + vb->cmd_id_received != vb->cmd_id_active) {
> + 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 update_balloon_size(struct virtio_balloon *vb)
> {
> u32 actual = vb->num_pages;
> @@ -425,44 +470,253 @@ static void update_balloon_size_func(struct work_struct *work)
> queue_work(system_freezable_wq, work);
> }
>
> +static void free_page_vq_cb(struct virtqueue *vq)
> +{
> + unsigned int len;
> + void *buf;
> + struct virtio_balloon *vb = vq->vdev->priv;
> +
> + while (1) {
> + buf = virtqueue_get_buf(vq, &len);
> +
> + if (!buf || buf == &vb->cmd_start || buf == &vb->cmd_stop)
> + break;
If there's any buffer after this one we might never get another
callback.
> + free_pages((unsigned long)buf, ARRAY_ALLOC_ORDER);
> + }
> +}
> +
> 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[VIRTIO_BALLOON_VQ_MAX];
> + vq_callback_t *callbacks[VIRTIO_BALLOON_VQ_MAX];
> + const char *names[VIRTIO_BALLOON_VQ_MAX];
> + struct scatterlist sg;
> + int ret;
>
> /*
> - * We expect two virtqueues: inflate and deflate, and
> - * optionally stat.
> + * Inflateq and deflateq are used unconditionally. The names[]
> + * will be NULL if the related feature is not enabled, which will
> + * cause no allocation for the corresponding virtqueue in find_vqs.
> */
> - 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 (err)
> - return err;
> + callbacks[VIRTIO_BALLOON_VQ_INFLATE] = balloon_ack;
> + names[VIRTIO_BALLOON_VQ_INFLATE] = "inflate";
> + callbacks[VIRTIO_BALLOON_VQ_DEFLATE] = balloon_ack;
> + names[VIRTIO_BALLOON_VQ_DEFLATE] = "deflate";
> + names[VIRTIO_BALLOON_VQ_STATS] = NULL;
> + names[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
>
> - vb->inflate_vq = vqs[0];
> - vb->deflate_vq = vqs[1];
> if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
> - struct scatterlist sg;
> - unsigned int num_stats;
> - vb->stats_vq = vqs[2];
> + names[VIRTIO_BALLOON_VQ_STATS] = "stats";
> + callbacks[VIRTIO_BALLOON_VQ_STATS] = stats_request;
> + }
>
> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
> + names[VIRTIO_BALLOON_VQ_FREE_PAGE] = "free_page_vq";
> + callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = free_page_vq_cb;
> + }
> +
> + ret = vb->vdev->config->find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX,
> + vqs, callbacks, names, NULL, NULL);
> + if (ret)
> + return ret;
> +
> + vb->inflate_vq = vqs[VIRTIO_BALLOON_VQ_INFLATE];
> + vb->deflate_vq = vqs[VIRTIO_BALLOON_VQ_DEFLATE];
> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
> + vb->stats_vq = vqs[VIRTIO_BALLOON_VQ_STATS];
> /*
> * 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);
> - if (virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb, GFP_KERNEL)
> - < 0)
> - BUG();
> + sg_init_one(&sg, vb->stats, sizeof(vb->stats));
> + ret = virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb,
> + GFP_KERNEL);
> + if (ret) {
> + dev_warn(&vb->vdev->dev, "%s: add stat_vq failed\n",
> + __func__);
> + return ret;
> + }
Why the change? Is it more likely to happen now?
> virtqueue_kick(vb->stats_vq);
> }
> +
> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
> + vb->free_page_vq = vqs[VIRTIO_BALLOON_VQ_FREE_PAGE];
> +
> return 0;
> }
>
> +static int send_start_cmd_id(struct virtio_balloon *vb)
> +{
> + struct scatterlist sg;
> + struct virtqueue *vq = vb->free_page_vq;
> +
> + vb->cmd_start.id = cpu_to_virtio32(vb->vdev, vb->cmd_id_active);
> + vb->cmd_start.size = cpu_to_virtio32(vb->vdev,
> + MAX_ORDER_NR_PAGES * PAGE_SIZE);
> + sg_init_one(&sg, &vb->cmd_start,
> + sizeof(struct virtio_balloon_free_page_hints_cmd));
> + return virtqueue_add_outbuf(vq, &sg, 1, &vb->cmd_start, GFP_KERNEL);
> +}
> +
> +static int send_stop_cmd_id(struct virtio_balloon *vb)
> +{
> + struct scatterlist sg;
> + struct virtqueue *vq = vb->free_page_vq;
> +
> + vb->cmd_stop.id = cpu_to_virtio32(vb->vdev,
> + VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID);
> + vb->cmd_stop.size = 0;
> + sg_init_one(&sg, &vb->cmd_stop,
> + sizeof(struct virtio_balloon_free_page_hints_cmd));
> + return virtqueue_add_outbuf(vq, &sg, 1, &vb->cmd_stop, GFP_KERNEL);
> +}
> +
> +/*
> + * virtio_balloon_send_hints - send arrays of hints to host
> + * @vb: the virtio_balloon struct
> + * @arrays: the arrays of hints
> + * @array_num: the number of arrays give by the caller
> + * @last_array_hints: the number of hints in the last array
> + *
> + * Send hints to host array by array. This begins by sending a start cmd,
> + * which contains a cmd id received from host and the free page block size in
> + * bytes of each hint. At the end, a stop cmd is sent to host to indicate the
> + * end of this reporting. If host actively requests to stop the reporting, free
> + * the arrays that have not been sent.
> + */
> +static void virtio_balloon_send_hints(struct virtio_balloon *vb,
> + __le64 **arrays,
> + uint32_t array_num,
> + uint32_t last_array_hints)
> +{
> + int err, i = 0;
> + struct scatterlist sg;
> + struct virtqueue *vq = vb->free_page_vq;
> +
> + /* Start by sending the received cmd id to host with an outbuf. */
> + err = send_start_cmd_id(vb);
> + if (unlikely(err))
> + goto out_err;
> + /* Kick host to start taking entries from the vq. */
> + virtqueue_kick(vq);
> +
> + for (i = 0; i < array_num; i++) {
> + /*
> + * If a stop id or a new cmd id was just received from host,
> + * stop the reporting, and free the remaining arrays that
> + * haven't been sent to host.
> + */
> + if (vb->cmd_id_received != vb->cmd_id_active)
> + goto out_free;
> +
> + if (i + 1 == array_num)
> + sg_init_one(&sg, (void *)arrays[i],
> + last_array_hints * sizeof(__le64));
> + else
> + sg_init_one(&sg, (void *)arrays[i], ARRAY_ALLOC_SIZE);
> + err = virtqueue_add_inbuf(vq, &sg, 1, (void *)arrays[i],
> + GFP_KERNEL);
> + if (unlikely(err))
> + goto out_err;
> + }
> +
> + /* End by sending a stop id to host with an outbuf. */
> + err = send_stop_cmd_id(vb);
> + if (unlikely(err))
> + goto out_err;
Don't we need to kick here?
> + return;
> +
> +out_err:
> + dev_err(&vb->vdev->dev, "%s: err = %d\n", __func__, err);
> +out_free:
> + while (i < array_num)
> + free_pages((unsigned long)arrays[i++], ARRAY_ALLOC_ORDER);
> +}
> +
> +/*
> + * virtio_balloon_load_hints - load free page hints into arrays
> + * @vb: the virtio_balloon struct
> + * @array_num: the number of arrays allocated
> + * @last_array_hints: the number of hints loaded into the last array
> + *
> + * Only free pages blocks of MAX_ORDER - 1 are loaded into the arrays.
> + * Each array size is MAX_ORDER_NR_PAGES * PAGE_SIZE (e.g. 4MB on x86). Failing
> + * to allocate such an array essentially implies that no such free page blocks
> + * could be reported. Alloacte the number of arrays according to the free page
> + * blocks of MAX_ORDER - 1 that the system may have, and free the unused ones
> + * after loading the free page hints. The last array may be partially loaded,
> + * and @last_array_hints tells the caller about the number of hints there.
> + *
> + * Return the pointer to the memory that holds the addresses of the allocated
> + * arrays, or NULL if no arrays are allocated.
> + */
> +static __le64 **virtio_balloon_load_hints(struct virtio_balloon *vb,
> + uint32_t *array_num,
> + uint32_t *last_array_hints)
> +{
> + __le64 **arrays;
> + uint32_t max_entries, entries_per_page, entries_per_array,
> + max_array_num, loaded_hints;
All above likely should be int.
> + int i;
> +
> + max_entries = max_free_page_blocks(ARRAY_ALLOC_ORDER);
> + entries_per_page = PAGE_SIZE / sizeof(__le64);
> + entries_per_array = entries_per_page * (1 << ARRAY_ALLOC_ORDER);
> + max_array_num = max_entries / entries_per_array +
> + !!(max_entries % entries_per_array);
> + arrays = kmalloc_array(max_array_num, sizeof(__le64 *), GFP_KERNEL);
Instead of all this mess, how about get_free_pages here as well?
Also why do we need GFP_KERNEL for this?
> + if (!arrays)
> + return NULL;
> +
> + for (i = 0; i < max_array_num; i++) {
So we are getting a ton of memory here just to free it up a bit later.
Why doesn't get_from_free_page_list get the pages from free list for us?
We could also avoid the 1st allocation then - just build a list
of these.
> + arrays[i] =
> + (__le64 *)__get_free_pages(__GFP_ATOMIC | __GFP_NOMEMALLOC,
> + ARRAY_ALLOC_ORDER);
Coding style says:
Descendants are always substantially shorter than the parent and
are placed substantially to the right.
> + if (!arrays[i]) {
Also if it does fail (small guest), shall we try with less arrays?
> + /*
> + * If any one of the arrays fails to be allocated, it
> + * implies that the free list that we are interested
> + * in is empty, and there is no need to continue the
> + * reporting. So just free what's allocated and return
> + * NULL.
> + */
> + while (i > 0)
> + free_pages((unsigned long)arrays[i--],
> + ARRAY_ALLOC_ORDER);
> + kfree(arrays);
> + return NULL;
> + }
> + }
> + loaded_hints = get_from_free_page_list(ARRAY_ALLOC_ORDER,
> + max_array_num, arrays,
> + entries_per_array);
> + *array_num = loaded_hints / entries_per_array +
> + !!(max_entries % entries_per_array);
> + *last_array_hints = loaded_hints -
> + (*array_num - 1) * entries_per_array;
> + for (i = *array_num; i < max_array_num; i++)
> + free_pages((unsigned long)arrays[i], ARRAY_ALLOC_ORDER);
> +
> + return arrays;
> +}
> +
> +static void report_free_page_func(struct work_struct *work)
> +{
> + struct virtio_balloon *vb;
> + uint32_t array_num = 0, last_array_hints = 0;
> + __le64 **arrays;
> +
> + vb = container_of(work, struct virtio_balloon, report_free_page_work);
> + vb->cmd_id_active = vb->cmd_id_received;
> +
> + arrays = virtio_balloon_load_hints(vb, &array_num, &last_array_hints);
> + if (arrays) {
> + virtio_balloon_send_hints(vb, arrays, array_num,
> + last_array_hints);
> + kfree(arrays);
> + }
> +}
> +
> #ifdef CONFIG_BALLOON_COMPACTION
> /*
> * virtballoon_migratepage - perform the balloon page migration on behalf of
> @@ -576,18 +830,30 @@ static int virtballoon_probe(struct virtio_device *vdev)
> if (err)
> goto out_free_vb;
>
> + if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
> + vb->balloon_wq = alloc_workqueue("balloon-wq",
> + WQ_FREEZABLE | WQ_CPU_INTENSIVE, 0);
> + if (!vb->balloon_wq) {
> + err = -ENOMEM;
> + goto out_del_vqs;
> + }
> + INIT_WORK(&vb->report_free_page_work, report_free_page_func);
> + vb->cmd_id_received = VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID;
> + vb->cmd_id_active = VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID;
> + }
> +
> vb->nb.notifier_call = virtballoon_oom_notify;
> vb->nb.priority = VIRTBALLOON_OOM_NOTIFY_PRIORITY;
> err = register_oom_notifier(&vb->nb);
> if (err < 0)
> - goto out_del_vqs;
> + goto out_del_balloon_wq;
>
> #ifdef CONFIG_BALLOON_COMPACTION
> balloon_mnt = kern_mount(&balloon_fs);
> if (IS_ERR(balloon_mnt)) {
> err = PTR_ERR(balloon_mnt);
> unregister_oom_notifier(&vb->nb);
> - goto out_del_vqs;
> + goto out_del_balloon_wq;
> }
>
> vb->vb_dev_info.migratepage = virtballoon_migratepage;
> @@ -597,7 +863,7 @@ static int virtballoon_probe(struct virtio_device *vdev)
> kern_unmount(balloon_mnt);
> unregister_oom_notifier(&vb->nb);
> vb->vb_dev_info.inode = NULL;
> - goto out_del_vqs;
> + goto out_del_balloon_wq;
> }
> vb->vb_dev_info.inode->i_mapping->a_ops = &balloon_aops;
> #endif
> @@ -608,6 +874,9 @@ static int virtballoon_probe(struct virtio_device *vdev)
> virtballoon_changed(vdev);
> return 0;
>
> +out_del_balloon_wq:
> + if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
> + destroy_workqueue(vb->balloon_wq);
> out_del_vqs:
> vdev->config->del_vqs(vdev);
> out_free_vb:
> @@ -641,6 +910,11 @@ static void virtballoon_remove(struct virtio_device *vdev)
> cancel_work_sync(&vb->update_balloon_size_work);
> cancel_work_sync(&vb->update_balloon_stats_work);
>
> + if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
> + cancel_work_sync(&vb->report_free_page_work);
> + destroy_workqueue(vb->balloon_wq);
> + }
> +
> remove_common(vb);
> #ifdef CONFIG_BALLOON_COMPACTION
> if (vb->vb_dev_info.inode)
> @@ -692,6 +966,7 @@ static unsigned int features[] = {
> VIRTIO_BALLOON_F_MUST_TELL_HOST,
> VIRTIO_BALLOON_F_STATS_VQ,
> VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
> + VIRTIO_BALLOON_F_FREE_PAGE_HINT,
> };
>
> static struct virtio_driver virtio_balloon_driver = {
> diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
> index 13b8cb5..860456f 100644
> --- a/include/uapi/linux/virtio_balloon.h
> +++ b/include/uapi/linux/virtio_balloon.h
> @@ -34,15 +34,26 @@
> #define VIRTIO_BALLOON_F_MUST_TELL_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_HINT 3 /* VQ to report free pages */
>
> /* 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;
> /* Number of pages we've actually got in balloon. */
> __u32 actual;
> + /* Free page report command id, readonly by guest */
> + __u32 free_page_report_cmd_id;
> +};
> +
> +struct virtio_balloon_free_page_hints_cmd {
> + /* The command id received from host */
> + __le32 id;
> + /* The free page block size in bytes */
> + __le32 size;
> };
>
> #define VIRTIO_BALLOON_S_SWAP_IN 0 /* Amount of memory swapped in */
> --
> 2.7.4