[PATCH v34 2/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

[Wei Wang <wei.w.wang@intel.com>]

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@intel.com>
Signed-off-by: Liang Li <liang.z.li@intel.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
 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)
+
 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;
 
@@ -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;
+		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;
+		}
 		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;
+	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;
+	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);
+	if (!arrays)
+		return NULL;
+
+	for (i = 0; i < max_array_num; i++) {
+		arrays[i] =
+		(__le64 *)__get_free_pages(__GFP_ATOMIC | __GFP_NOMEMALLOC,
+					   ARRAY_ALLOC_ORDER);
+		if (!arrays[i]) {
+			/*
+			 * 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