[RFC PATCH 10/11] virtio-balloon: Add support for aerating memory via bubble hinting

[Alexander Duyck]

From: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>

Add support for aerating memory using the bubble hinting feature provided
by virtio-balloon. Bubble 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@xxxxxxxxxxxxxxx>
---
 drivers/virtio/Kconfig              |    1 
 drivers/virtio/virtio_balloon.c     |   89 +++++++++++++++++++++++++++++++++++
 include/uapi/linux/virtio_balloon.h |    1 
 3 files changed, 90 insertions(+), 1 deletion(-)

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..e1399991bc1f 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
@@ -45,6 +46,7 @@ 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
 };
 
@@ -52,9 +54,16 @@ enum virtio_balloon_config_read {
 	VIRTIO_BALLOON_CONFIG_READ_CMD_ID = 0,
 };
 
+#define VIRTIO_BUBBLE_ARRAY_HINTS_MAX	32
+struct virtio_bubble_page_hint {
+	__virtio32 pfn;
+	__virtio32 size;
+};
+
 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;
@@ -107,6 +116,11 @@ struct virtio_balloon {
 	unsigned int num_pfns;
 	__virtio32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];
 
+	/* The array of PFNs we are hinting on */
+	unsigned int num_hints;
+	struct virtio_bubble_page_hint hints[VIRTIO_BUBBLE_ARRAY_HINTS_MAX];
+	struct aerator_dev_info a_dev_info;
+
 	/* Memory statistics */
 	struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
 
@@ -151,6 +165,54 @@ static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
 
 }
 
+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;
+
+	vb->num_hints = 0;
+
+	list_for_each_entry(page, &a_dev_info->batch_reactor, lru) {
+		struct virtio_bubble_page_hint *hint;
+		unsigned int size;
+
+		hint = &vb->hints[vb->num_hints++];
+		hint->pfn = cpu_to_virtio32(vb->vdev,
+					    page_to_balloon_pfn(page));
+		size = VIRTIO_BALLOON_PAGES_PER_PAGE << page_private(page);
+		hint->size = cpu_to_virtio32(vb->vdev, size);
+	}
+
+	/* We shouldn't have been called if there is nothing to process */
+	if (WARN_ON(vb->num_hints == 0))
+		return;
+
+	/* Detach all the used buffers from the vq */
+	while (virtqueue_get_buf(vq, &unused))
+		;
+
+	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);
+}
+
+static void aerator_settled(struct virtqueue *vq)
+{
+	/* Drain the current aerator contents, refill, and start next cycle */
+	aerator_cycle();
+}
+
 static void set_page_pfns(struct virtio_balloon *vb,
 			  __virtio32 pfns[], struct page *page)
 {
@@ -475,6 +537,7 @@ 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 +549,19 @@ 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] = aerator_settled;
+	}
+
 	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 +1000,25 @@ 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_BUBBLE_ARRAY_HINTS_MAX;
+	INIT_LIST_HEAD(&vb->a_dev_info.batch_reactor);
+	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 +1047,8 @@ 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 +1118,7 @@ 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