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Subject: Re: [PATCH v2 5/5] virtio-balloon: Add support for providing page
 hints to host
To:     Alexander Duyck <alexander.duyck@gmail.com>, kvm@vger.kernel.org,
        david@redhat.com, mst@redhat.com, dave.hansen@intel.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        akpm@linux-foundation.org
Cc:     yang.zhang.wz@gmail.com, pagupta@redhat.com, riel@surriel.com,
        konrad.wilk@oracle.com, lcapitulino@redhat.com,
        wei.w.wang@intel.com, aarcange@redhat.com, pbonzini@redhat.com,
        dan.j.williams@intel.com, alexander.h.duyck@linux.intel.com
References: <20190724165158.6685.87228.stgit@localhost.localdomain>
 <20190724170514.6685.17161.stgit@localhost.localdomain>
From:   Nitesh Narayan Lal <nitesh@redhat.com>
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Organization: Red Hat Inc,
Message-ID: <fc99b28d-2efd-cd05-59e4-99f35bd37cac@redhat.com>
Date:   Thu, 25 Jul 2019 13:42:41 -0400
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On 7/24/19 1:05 PM, Alexander Duyck wrote:
> From: Alexander Duyck <alexander.h.duyck@linux.intel.com>
>
> Add support for the page 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     |   47 +++++++++++++++++++++++++++++++++++
>  include/uapi/linux/virtio_balloon.h |    1 +
>  3 files changed, 49 insertions(+)
>
> diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
> index 078615cf2afc..d45556ae1f81 100644
> --- a/drivers/virtio/Kconfig
> +++ b/drivers/virtio/Kconfig
> @@ -58,6 +58,7 @@ 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 226fbb995fb0..dee9f8f3ad09 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -19,6 +19,7 @@
>  #include <linux/mount.h>
>  #include <linux/magic.h>
>  #include <linux/pseudo_fs.h>
> +#include <linux/page_hinting.h>
>  
>  /*
>   * Balloon device works in 4K page units.  So each page is pointed to by
> @@ -27,6 +28,7 @@
>   */
>  #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 | \
> @@ -46,6 +48,7 @@ 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
>  };
>  
> @@ -113,6 +116,10 @@ struct virtio_balloon {
>  
>  	/* To register a shrinker to shrink memory upon memory pressure */
>  	struct shrinker shrinker;
> +
> +	/* Unused page hinting device */
> +	struct virtqueue *hinting_vq;
> +	struct page_hinting_dev_info ph_dev_info;
>  };
>  
>  static struct virtio_device_id id_table[] = {
> @@ -152,6 +159,22 @@ static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
>  
>  }
>  
> +void virtballoon_page_hinting_react(struct page_hinting_dev_info *ph_dev_info,
> +				    unsigned int num_hints)
> +{
> +	struct virtio_balloon *vb =
> +		container_of(ph_dev_info, struct virtio_balloon, ph_dev_info);
> +	struct virtqueue *vq = vb->hinting_vq;
> +	unsigned int unused;
> +
> +	/* We should always be able to add these buffers to an empty queue. */
> +	virtqueue_add_inbuf(vq, ph_dev_info->sg, num_hints, 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));
> +}
> +
>  static void set_page_pfns(struct virtio_balloon *vb,
>  			  __virtio32 pfns[], struct page *page)
>  {
> @@ -476,6 +499,7 @@ 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";
> @@ -487,11 +511,19 @@ 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)) {
> @@ -924,12 +956,24 @@ static int virtballoon_probe(struct virtio_device *vdev)
>  		if (err)
>  			goto out_del_balloon_wq;
>  	}
> +
> +	vb->ph_dev_info.react = virtballoon_page_hinting_react;
> +	vb->ph_dev_info.capacity = VIRTIO_BALLOON_ARRAY_HINTS_MAX;
> +	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_HINTING)) {
> +		err = page_hinting_startup(&vb->ph_dev_info);
> +		if (err)
> +			goto out_unregister_shrinker;
> +	}
Any reason why you have kept vb->ph_dev_info.react & vb->ph_dev_info.capacity
initialization outside the feature check?
> +
>  	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);
> @@ -958,6 +1002,8 @@ static void virtballoon_remove(struct virtio_device *vdev)
>  {
>  	struct virtio_balloon *vb = vdev->priv;
>  
> +	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_HINTING))
> +		page_hinting_shutdown(&vb->ph_dev_info);
>  	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
>  		virtio_balloon_unregister_shrinker(vb);
>  	spin_lock_irq(&vb->stop_update_lock);
> @@ -1027,6 +1073,7 @@ 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
>
-- 
Thanks
Nitesh