Re: [PATCH v1 6/6] virtio-balloon: Add support for aerating memory via hinting

Michael S. Tsirkin
2019-07-16T09:55:57Z

On Wed, Jun 19, 2019 at 03:33:38PM -0700, Alexander Duyck wrote:
> From: Alexander Duyck <alexander.h.duyck@linux.intel.com>
>
> Add support for aerating memory using the hinting feature provided by
> virtio-balloon. Hinting differs from the regular balloon functionality in
> that is is much less durable than a standard memory balloon. Instead of
> creating a list of pages that cannot be accessed the pages are only
> inaccessible while they are being indicated to the virtio interface. Once
> the interface has acknowledged them they are placed back into their
> respective free lists and are once again accessible by the guest system.
>
> Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> ---
> drivers/virtio/Kconfig | 1
> drivers/virtio/virtio_balloon.c | 110 ++++++++++++++++++++++++++++++++++-
> include/uapi/linux/virtio_balloon.h | 1
> 3 files changed, 108 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
> index 023fc3bc01c6..9cdaccf92c3a 100644
> --- a/drivers/virtio/Kconfig
> +++ b/drivers/virtio/Kconfig
> @@ -47,6 +47,7 @@ config VIRTIO_BALLOON
> tristate "Virtio balloon driver"
> depends on VIRTIO
> select MEMORY_BALLOON
> + select AERATION
> ---help---
> This driver supports increasing and decreasing the amount
> of memory within a KVM guest.
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 44339fc87cc7..91f1e8c9017d 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -18,6 +18,7 @@
> #include <linux/mm.h>
> #include <linux/mount.h>
> #include <linux/magic.h>
> +#include <linux/memory_aeration.h>
>
> /*
> * Balloon device works in 4K page units. So each page is pointed to by
> @@ -26,6 +27,7 @@
> */
> #define VIRTIO_BALLOON_PAGES_PER_PAGE (unsigned)(PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)
> #define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256
> +#define VIRTIO_BALLOON_ARRAY_HINTS_MAX 32
> #define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80
>
> #define VIRTIO_BALLOON_FREE_PAGE_ALLOC_FLAG (__GFP_NORETRY | __GFP_NOWARN | \
> @@ -45,6 +47,7 @@ enum virtio_balloon_vq {
> VIRTIO_BALLOON_VQ_DEFLATE,
> VIRTIO_BALLOON_VQ_STATS,
> VIRTIO_BALLOON_VQ_FREE_PAGE,
> + VIRTIO_BALLOON_VQ_HINTING,
> VIRTIO_BALLOON_VQ_MAX
> };
>
> @@ -54,7 +57,8 @@ enum virtio_balloon_config_read {
>
> struct virtio_balloon {
> struct virtio_device *vdev;
> - struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *free_page_vq;
> + struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *free_page_vq,
> + *hinting_vq;
>
> /* Balloon's own wq for cpu-intensive work items */
> struct workqueue_struct *balloon_wq;
> @@ -103,9 +107,21 @@ struct virtio_balloon {
> /* Synchronize access/update to this struct virtio_balloon elements */
> struct mutex balloon_lock;
>
> - /* The array of pfns we tell the Host about. */
> - unsigned int num_pfns;
> - __virtio32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];
> +
> + union {
> + /* The array of pfns we tell the Host about. */
> + struct {
> + unsigned int num_pfns;
> + __virtio32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];
> + };
> + /* The array of physical addresses we are hinting on */
> + struct {
> + unsigned int num_hints;
> + __virtio64 hints[VIRTIO_BALLOON_ARRAY_HINTS_MAX];
> + };
> + };
> +
> + struct aerator_dev_info a_dev_info;
>
> /* Memory statistics */
> struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
> @@ -151,6 +167,68 @@ static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
>
> }
>
> +static u64 page_to_hints_pa_order(struct page *page)
> +{
> + unsigned char order;
> + dma_addr_t pa;
> +
> + BUILD_BUG_ON((64 - VIRTIO_BALLOON_PFN_SHIFT) >=
> + (1 << VIRTIO_BALLOON_PFN_SHIFT));
> +
> + /*
> + * Record physical page address combined with page order.
> + * Order will never exceed 64 - VIRTIO_BALLON_PFN_SHIFT
> + * since the size has to fit into a 64b value. So as long
> + * as VIRTIO_BALLOON_SHIFT is greater than this combining
> + * the two values should be safe.
> + */
> + pa = page_to_phys(page);
> + order = page_private(page) +
> + PAGE_SHIFT - VIRTIO_BALLOON_PFN_SHIFT;
> +
> + return (u64)(pa | order);
> +}
> +
> +void virtballoon_aerator_react(struct aerator_dev_info *a_dev_info)
> +{
> + struct virtio_balloon *vb = container_of(a_dev_info,
> + struct virtio_balloon,
> + a_dev_info);
> + struct virtqueue *vq = vb->hinting_vq;
> + struct scatterlist sg;
> + unsigned int unused;
> + struct page *page;
> +
> + mutex_lock(&vb->balloon_lock);
> +
> + vb->num_hints = 0;
> +
> + list_for_each_entry(page, &a_dev_info->batch, lru) {
> + vb->hints[vb->num_hints++] =
> + cpu_to_virtio64(vb->vdev,
> + page_to_hints_pa_order(page));
> + }
> +
> + /* We shouldn't have been called if there is nothing to process */
> + if (WARN_ON(vb->num_hints == 0))
> + goto out;
> +
> + sg_init_one(&sg, vb->hints,
> + sizeof(vb->hints[0]) * vb->num_hints);
> +
> + /*
> + * We should always be able to add one buffer to an
> + * empty queue.
> + */
> + virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
> + virtqueue_kick(vq);
> +
> + /* When host has read buffer, this completes via balloon_ack */
> + wait_event(vb->acked, virtqueue_get_buf(vq, &unused));
> +out:
> + mutex_unlock(&vb->balloon_lock);
> +}
> +
> static void set_page_pfns(struct virtio_balloon *vb,
> __virtio32 pfns[], struct page *page)
> {
> @@ -475,6 +553,7 @@ static int init_vqs(struct virtio_balloon *vb)
> names[VIRTIO_BALLOON_VQ_DEFLATE] = "deflate";
> names[VIRTIO_BALLOON_VQ_STATS] = NULL;
> names[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
> + names[VIRTIO_BALLOON_VQ_HINTING] = NULL;
>
> if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
> names[VIRTIO_BALLOON_VQ_STATS] = "stats";
> @@ -486,11 +565,19 @@ static int init_vqs(struct virtio_balloon *vb)
> callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
> }
>
> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_HINTING)) {
> + names[VIRTIO_BALLOON_VQ_HINTING] = "hinting_vq";
> + callbacks[VIRTIO_BALLOON_VQ_HINTING] = balloon_ack;
> + }
> +
> err = vb->vdev->config->find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX,
> vqs, callbacks, names, NULL, NULL);
> if (err)
> return err;
>
> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_HINTING))
> + vb->hinting_vq = vqs[VIRTIO_BALLOON_VQ_HINTING];
> +
> 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)) {
> @@ -929,12 +1016,24 @@ static int virtballoon_probe(struct virtio_device *vdev)
> if (err)
> goto out_del_balloon_wq;
> }
> +
> + vb->a_dev_info.react = virtballoon_aerator_react;
> + vb->a_dev_info.capacity = VIRTIO_BALLOON_ARRAY_HINTS_MAX;
> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_HINTING)) {
> + err = aerator_startup(&vb->a_dev_info);
> + if (err)
> + goto out_unregister_shrinker;
> + }
> +
> virtio_device_ready(vdev);
>
> if (towards_target(vb))
> virtballoon_changed(vdev);
> return 0;
>
> +out_unregister_shrinker:
> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
> + virtio_balloon_unregister_shrinker(vb);
> out_del_balloon_wq:
> if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
> destroy_workqueue(vb->balloon_wq);
> @@ -963,6 +1062,8 @@ static void virtballoon_remove(struct virtio_device *vdev)
> {
> struct virtio_balloon *vb = vdev->priv;
>
> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_HINTING))
> + aerator_shutdown();
> if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
> virtio_balloon_unregister_shrinker(vb);
> spin_lock_irq(&vb->stop_update_lock);
> @@ -1032,6 +1133,7 @@ static int virtballoon_validate(struct virtio_device *vdev)
> VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
> VIRTIO_BALLOON_F_FREE_PAGE_HINT,
> VIRTIO_BALLOON_F_PAGE_POISON,
> + VIRTIO_BALLOON_F_HINTING,
> };
>
> static struct virtio_driver virtio_balloon_driver = {
> diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
> index a1966cd7b677..2b0f62814e22 100644
> --- a/include/uapi/linux/virtio_balloon.h
> +++ b/include/uapi/linux/virtio_balloon.h
> @@ -36,6 +36,7 @@
> #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 */
> #define VIRTIO_BALLOON_F_PAGE_POISON 4 /* Guest is using page poisoning */
> +#define VIRTIO_BALLOON_F_HINTING 5 /* Page hinting virtqueue */
>
> /* Size of a PFN in the balloon interface. */
> #define VIRTIO_BALLOON_PFN_SHIFT 12

The approach here is very close to what on-demand hinting that is
already upstream does.

This should have resulted in a most of the code being shared
but this does not seem to happen here.

Can we unify the code in some way?
It can still use a separate feature flag, but there are things
I like very much about current hinting code, such as
using s/g instead of passing PFNs in a buffer.

If this doesn't work could you elaborate on why?

--
MST