Re: [RFC][Patch v11 2/2] virtio-balloon: page_hinting: reporting to the host

From: Michael S. Tsirkin
Date: Wed Jul 24 2019 - 15:47:47 EST

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On Wed, Jul 10, 2019 at 03:51:58PM -0400, Nitesh Narayan Lal wrote:
> Enables the kernel to negotiate VIRTIO_BALLOON_F_HINTING feature with the
> host. If it is available and page_hinting_flag is set to true, page_hinting
> is enabled and its callbacks are configured along with the max_pages count
> which indicates the maximum number of pages that can be isolated and hinted
> at a time. Currently, only free pages of order >= (MAX_ORDER - 2) are
> reported. To prevent any false OOM max_pages count is set to 16.
>
> By default page_hinting feature is enabled and gets loaded as soon
> as the virtio-balloon driver is loaded. However, it could be disabled
> by writing the page_hinting_flag which is a virtio-balloon parameter.
>
> Signed-off-by: Nitesh Narayan Lal <nitesh@xxxxxxxxxx>
> ---
> drivers/virtio/Kconfig | 1 +
> drivers/virtio/virtio_balloon.c | 91 ++++++++++++++++++++++++++++-
> include/uapi/linux/virtio_balloon.h | 11 ++++
> 3 files changed, 102 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
> index 023fc3bc01c6..dcc0cb4269a5 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 PAGE_HINTING
> ---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..1fb0eb0b2c20 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/page_hinting.h>
>
> /*
> * Balloon device works in 4K page units. So each page is pointed to by
> @@ -35,6 +36,12 @@
> /* The size of a free page block in bytes */
> #define VIRTIO_BALLOON_FREE_PAGE_SIZE \
> (1 << (VIRTIO_BALLOON_FREE_PAGE_ORDER + PAGE_SHIFT))
> +/* Number of isolated pages to be reported to the host at a time.
> + * TODO:
> + * 1. Set it via host.
> + * 2. Find an optimal value for this.
> + */
> +#define PAGE_HINTING_MAX_PAGES 16
>
> #ifdef CONFIG_BALLOON_COMPACTION
> static struct vfsmount *balloon_mnt;
> @@ -45,6 +52,7 @@ 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 +62,8 @@ 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;
> @@ -112,6 +121,9 @@ struct virtio_balloon {
>
> /* To register a shrinker to shrink memory upon memory pressure */
> struct shrinker shrinker;
> +
> + /* Array object pointing at the isolated pages ready for hinting */
> + struct isolated_memory isolated_pages[PAGE_HINTING_MAX_PAGES];
> };
>
> static struct virtio_device_id id_table[] = {
> @@ -119,6 +131,66 @@ static struct virtio_device_id id_table[] = {
> { 0 },
> };
>
> +static struct page_hinting_config page_hinting_conf;
> +bool page_hinting_flag = true;
> +struct virtio_balloon *hvb;
> +module_param(page_hinting_flag, bool, 0444);
> +MODULE_PARM_DESC(page_hinting_flag, "Enable page hinting");
> +
> +static int page_hinting_report(void)
> +{
> + struct virtqueue *vq = hvb->hinting_vq;
> + struct scatterlist sg;
> + int err = 0, unused;
> +
> + mutex_lock(&hvb->balloon_lock);
> + sg_init_one(&sg, hvb->isolated_pages, sizeof(hvb->isolated_pages[0]) *
> + PAGE_HINTING_MAX_PAGES);
> + err = virtqueue_add_outbuf(vq, &sg, 1, hvb, GFP_KERNEL);

In Alex's patch, I really like it that he's passing pages as sg
entries. IMHO that's both cleaner and allows seamless
support for arbitrary page sizes.

In particular ....

> + if (!err)
> + virtqueue_kick(hvb->hinting_vq);
> + wait_event(hvb->acked, virtqueue_get_buf(vq, &unused));
> + mutex_unlock(&hvb->balloon_lock);
> + return err;
> +}
> +
> +void hint_pages(struct list_head *pages)
> +{
> + struct device *dev = &hvb->vdev->dev;
> + struct page *page, *next;
> + int idx = 0, order, err;
> + unsigned long pfn;
> +
> + list_for_each_entry_safe(page, next, pages, lru) {
> + pfn = page_to_pfn(page);
> + order = page_private(page);
> + hvb->isolated_pages[idx].phys_addr = pfn << PAGE_SHIFT;
> + hvb->isolated_pages[idx].size = (1 << order) * PAGE_SIZE;
> + idx++;

... passing native endian-ness values to host creates pain for
cross-endian configurations.

> + }
> + err = page_hinting_report();
> + if (err < 0)
> + dev_err(dev, "Failed to hint pages, err = %d\n", err);
> +}
> +
> +static void page_hinting_init(struct virtio_balloon *vb)
> +{
> + struct device *dev = &vb->vdev->dev;
> + int err;
> +
> + page_hinting_conf.hint_pages = hint_pages;
> + page_hinting_conf.max_pages = PAGE_HINTING_MAX_PAGES;
> + err = page_hinting_enable(&page_hinting_conf);
> + if (err < 0) {
> + dev_err(dev, "Failed to enable page-hinting, err = %d\n", err);

It would be nicer to disable the feature bit then, or fail probe
completely.

> + page_hinting_flag = false;
> + page_hinting_conf.hint_pages = NULL;
> + page_hinting_conf.max_pages = 0;
> + return;
> + }
> + hvb = vb;
> +}
> +
> static u32 page_to_balloon_pfn(struct page *page)
> {
> unsigned long pfn = page_to_pfn(page);
> @@ -475,6 +547,7 @@ 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 +559,18 @@ 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)) {
> @@ -929,6 +1009,9 @@ static int virtballoon_probe(struct virtio_device *vdev)
> if (err)
> goto out_del_balloon_wq;
> }
> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_HINTING) &&
> + page_hinting_flag)
> + page_hinting_init(vb);
> virtio_device_ready(vdev);
>
> if (towards_target(vb))
> @@ -976,6 +1059,10 @@ static void virtballoon_remove(struct virtio_device *vdev)
> destroy_workqueue(vb->balloon_wq);
> }
>
> + if (!page_hinting_flag) {
> + hvb = NULL;
> + page_hinting_disable();
> + }
> remove_common(vb);
> #ifdef CONFIG_BALLOON_COMPACTION
> if (vb->vb_dev_info.inode)
> @@ -1030,8 +1117,10 @@ static unsigned int features[] = {
> VIRTIO_BALLOON_F_MUST_TELL_HOST,
> VIRTIO_BALLOON_F_STATS_VQ,
> VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
> + VIRTIO_BALLOON_F_HINTING,
> 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..29eed0ec83d3 100644
> --- a/include/uapi/linux/virtio_balloon.h
> +++ b/include/uapi/linux/virtio_balloon.h
> @@ -36,6 +36,8 @@
> #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 */
> +/* TODO: Find a better name to avoid any confusion with FREE_PAGE_HINT */
> +#define VIRTIO_BALLOON_F_HINTING 5 /* Page hinting virtqueue */
>
> /* Size of a PFN in the balloon interface. */
> #define VIRTIO_BALLOON_PFN_SHIFT 12
> @@ -108,4 +110,13 @@ struct virtio_balloon_stat {
> __virtio64 val;
> } __attribute__((packed));
>
> +/*
> + * struct isolated_memory- holds the pages which will be reported to the host.
> + * @phys_add: physical address associated with a page.
> + * @size: total size of memory to be reported.
> + */
> +struct isolated_memory {
> + __virtio64 phys_addr;
> + __virtio64 size;
> +};
> #endif /* _LINUX_VIRTIO_BALLOON_H */
> --
> 2.21.0

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