[PATCH v29 2/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

[Wei Wang]

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.

When the guest starts to report, the first element added to the free page
vq is the cmd id given by host. When the guest finishes the reporting
of all the free pages, VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID is added
to the vq to tell host that the reporting is done. Host polls the free
page vq after sending the starting cmd id, so the guest doesn't need to
kick after filling an element to the vq.

Host may also requests the guest to stop the reporting in advance by
sending the stop cmd id to the guest via the configuration register.

Signed-off-by: Wei Wang 
Signed-off-by: Liang Li 
Cc: Michael S. Tsirkin 
Cc: Michal Hocko 
---
 drivers/virtio/virtio_balloon.c | 257 +++-
 include/uapi/linux/virtio_balloon.h |   4 +
 2 files changed, 225 insertions(+), 36 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index dfe5684..18d24a4 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -51,9 +51,22 @@ 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 +76,13 @@ struct virtio_balloon {
spinlock_t stop_update_lock;
bool stop_update;
 
+   /* The new cmd id received from host */
+   uint32_t cmd_id_received;
+   /* The cmd id that is in use */
+   __virtio32 cmd_id_use;
+   /* Buffer to store the stop sign */
+   __virtio32 stop_cmd_id;
+
/* Waiting for host to ack the pages we released. */
wait_queue_head_t acked;
 
@@ -320,17 +340,6 @@ 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(>stop_update_lock, flags);
-   if (!vb->stop_update)
-   queue_work(system_freezable_wq, >update_balloon_size_work);
-   spin_unlock_irqrestore(>stop_update_lock, flags);
-}
-
 static inline s64 towards_target(struct virtio_balloon *vb)
 {
s64 target;
@@ -347,6 +356,34 @@ 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(>stop_update_lock, flags);
+   if (!vb->stop_update)
+   queue_work(system_freezable_wq,
+  >update_balloon_size_work);
+   spin_unlock_irqrestore(>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, >cmd_id_received);
+   if (vb->cmd_id_received !=
+   VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID) {
+   spin_lock_irqsave(>stop_update_lock, flags);
+   if (!vb->stop_update)
+   queue_work(vb->balloon_wq,
+  >report_free_page_work);
+   spin_unlock_irqrestore(>stop_update_lock, flags);
+   }
+   }
+}
+
 static void update_balloon_size(struct virtio_balloon *vb)
 {
u32 actual = vb->num_pages;
@@ -421,42 +458,163 @@ static void update_balloon_size_func(struct work_struct 
*work)
 
 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, 

[PATCH v29 2/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

[Wei Wang]

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.

When the guest starts to report, the first element added to the free page
vq is the cmd id given by host. When the guest finishes the reporting
of all the free pages, VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID is added
to the vq to tell host that the reporting is done. Host polls the free
page vq after sending the starting cmd id, so the guest doesn't need to
kick after filling an element to the vq.

Host may also requests the guest to stop the reporting in advance by
sending the stop cmd id to the guest via the configuration register.

Signed-off-by: Wei Wang 
Signed-off-by: Liang Li 
Cc: Michael S. Tsirkin 
Cc: Michal Hocko 
---
 drivers/virtio/virtio_balloon.c | 257 +++-
 include/uapi/linux/virtio_balloon.h |   4 +
 2 files changed, 225 insertions(+), 36 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index dfe5684..18d24a4 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -51,9 +51,22 @@ 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 +76,13 @@ struct virtio_balloon {
spinlock_t stop_update_lock;
bool stop_update;
 
+   /* The new cmd id received from host */
+   uint32_t cmd_id_received;
+   /* The cmd id that is in use */
+   __virtio32 cmd_id_use;
+   /* Buffer to store the stop sign */
+   __virtio32 stop_cmd_id;
+
/* Waiting for host to ack the pages we released. */
wait_queue_head_t acked;
 
@@ -320,17 +340,6 @@ 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(>stop_update_lock, flags);
-   if (!vb->stop_update)
-   queue_work(system_freezable_wq, >update_balloon_size_work);
-   spin_unlock_irqrestore(>stop_update_lock, flags);
-}
-
 static inline s64 towards_target(struct virtio_balloon *vb)
 {
s64 target;
@@ -347,6 +356,34 @@ 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(>stop_update_lock, flags);
+   if (!vb->stop_update)
+   queue_work(system_freezable_wq,
+  >update_balloon_size_work);
+   spin_unlock_irqrestore(>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, >cmd_id_received);
+   if (vb->cmd_id_received !=
+   VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID) {
+   spin_lock_irqsave(>stop_update_lock, flags);
+   if (!vb->stop_update)
+   queue_work(vb->balloon_wq,
+  >report_free_page_work);
+   spin_unlock_irqrestore(>stop_update_lock, flags);
+   }
+   }
+}
+
 static void update_balloon_size(struct virtio_balloon *vb)
 {
u32 actual = vb->num_pages;
@@ -421,42 +458,163 @@ static void update_balloon_size_func(struct work_struct 
*work)
 
 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];
+