[Qemu-devel] virtio: Add memory statistics reporting to the balloon driver (V2)

[Adam Litke]

virtio: Add memory statistics reporting to the balloon driver (V2)

Changes since V1:
 - Use a virtqueue instead of the device config space

When using ballooning to manage overcommitted memory on a host, a system for
guests to communicate their memory usage to the host can provide information
that will minimize the impact of ballooning on the guests.  The current method
employs a daemon running in each guest that communicates memory statistics to a
host daemon at a specified time interval.  The host daemon aggregates this
information and inflates and/or deflates balloons according to the level of
host memory pressure.  This approach is effective but overly complex since a
daemon must be installed inside each guest and coordinated to communicate with
the host.  A simpler approach is to collect memory statistics in the virtio
balloon driver and communicate them directly to the hypervisor.

This patch enables the guest-side support by adding stats collection and
reporting to the virtio balloon driver.

Signed-off-by: Adam Litke <address@hidden>
Cc: Rusty Russell <address@hidden>
Cc: Anthony Liguori <address@hidden>
Cc: address@hidden
Cc: address@hidden

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 200c22f..59b9533 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -29,7 +29,7 @@
 struct virtio_balloon
 {
        struct virtio_device *vdev;
-       struct virtqueue *inflate_vq, *deflate_vq;
+       struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
 
        /* Where the ballooning thread waits for config to change. */
        wait_queue_head_t config_change;
@@ -50,6 +50,9 @@ struct virtio_balloon
        /* The array of pfns we tell the Host about. */
        unsigned int num_pfns;
        u32 pfns[256];
+
+       /* Memory statistics */
+       struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
 };
 
 static struct virtio_device_id id_table[] = {
@@ -155,6 +158,60 @@ static void leak_balloon(struct virtio_balloon *vb, size_t 
num)
        }
 }
 
+static inline void update_stat(struct virtio_balloon *vb, int idx,
+                               unsigned int tag, unsigned long val)
+{
+       BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
+       vb->stats[idx].tag = tag;
+       vb->stats[idx].val = cpu_to_le32(val);
+}
+
+#define K(x) ((x) << (PAGE_SHIFT - 10))
+static void update_balloon_stats(struct virtio_balloon *vb)
+{
+       unsigned long events[NR_VM_EVENT_ITEMS];
+       struct sysinfo i;
+       unsigned long anon_pages;
+       int idx = 0;
+
+       all_vm_events(events);
+       si_meminfo(&i);
+       anon_pages = K(global_page_state(NR_ANON_PAGES));
+
+       update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN, events[PSWPIN]);
+       update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT, events[PSWPOUT]);
+       update_stat(vb, idx++, VIRTIO_BALLOON_S_ANON, anon_pages);
+       update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
+       update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
+       update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE, K(i.freeram));
+       update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT, K(i.totalram));
+}
+
+/*
+ * While most virtqueues communicate guest-initiated requests to the 
hypervisor,
+ * the stats queue operates in reverse.  The driver initializes the virtqueue
+ * with a single buffer.  From that point forward, all conversations consist of
+ * a hypervisor request (a call to this function) which directs us to refill
+ * the virtqueue with a fresh stats buffer.
+ */
+static void stats_ack(struct virtqueue *vq)
+{
+       struct virtio_balloon *vb;
+       unsigned int len;
+       struct scatterlist sg;
+
+       vb = vq->vq_ops->get_buf(vq, &len);
+       if (!vb)
+               return;
+
+       update_balloon_stats(vb);
+
+       sg_init_one(&sg, vb->stats, sizeof(vb->stats));
+       if (vq->vq_ops->add_buf(vq, &sg, 1, 0, vb) < 0)
+               BUG();
+       vq->vq_ops->kick(vq);
+}
+
 static void virtballoon_changed(struct virtio_device *vdev)
 {
        struct virtio_balloon *vb = vdev->priv;
@@ -205,10 +262,10 @@ static int balloon(void *_vballoon)
 static int virtballoon_probe(struct virtio_device *vdev)
 {
        struct virtio_balloon *vb;
-       struct virtqueue *vqs[2];
-       vq_callback_t *callbacks[] = { balloon_ack, balloon_ack };
-       const char *names[] = { "inflate", "deflate" };
-       int err;
+       struct virtqueue *vqs[3];
+       vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_ack };
+       const char *names[] = { "inflate", "deflate", "stats" };
+       int err, nvqs;
 
        vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
        if (!vb) {
@@ -221,13 +278,28 @@ static int virtballoon_probe(struct virtio_device *vdev)
        init_waitqueue_head(&vb->config_change);
        vb->vdev = vdev;
 
-       /* We expect two virtqueues. */
-       err = vdev->config->find_vqs(vdev, 2, vqs, callbacks, names);
+       /* We expect two virtqueues: inflate and deflate,
+        * and optionally stat. */
+       nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
+       err = vdev->config->find_vqs(vdev, nvqs, vqs, callbacks, names);
        if (err)
                goto out_free_vb;
 
        vb->inflate_vq = vqs[0];
        vb->deflate_vq = vqs[1];
+       if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
+               struct scatterlist sg;
+               vb->stats_vq = vqs[2];
+
+               /*
+                * Prime this virtqueue with one buffer so the hypervisor can
+                * use it to signal us later.
+                */
+               sg_init_one(&sg, vb->stats, sizeof(vb->stats));
+               if (vb->stats_vq->vq_ops->add_buf(vb->stats_vq, &sg, 1, 0, vb) 
< 0)
+                       BUG();
+               vb->stats_vq->vq_ops->kick(vb->stats_vq);
+       }
 
        vb->thread = kthread_run(balloon, vb, "vballoon");
        if (IS_ERR(vb->thread)) {
@@ -265,7 +337,9 @@ static void virtballoon_remove(struct virtio_device *vdev)
        kfree(vb);
 }
 
-static unsigned int features[] = { VIRTIO_BALLOON_F_MUST_TELL_HOST };
+static unsigned int features[] = {
+       VIRTIO_BALLOON_F_MUST_TELL_HOST, VIRTIO_BALLOON_F_STATS_VQ,
+};
 
 static struct virtio_driver virtio_balloon = {
        .feature_table = features,
diff --git a/include/linux/virtio_balloon.h b/include/linux/virtio_balloon.h
index 09d7300..3d21b9f 100644
--- a/include/linux/virtio_balloon.h
+++ b/include/linux/virtio_balloon.h
@@ -6,6 +6,7 @@
 
 /* The feature bitmap for virtio balloon */
 #define VIRTIO_BALLOON_F_MUST_TELL_HOST        0 /* Tell before reclaiming 
pages */
+#define VIRTIO_BALLOON_F_STATS_VQ 1 /* Memory Stats virtqueue */
 
 /* Size of a PFN in the balloon interface. */
 #define VIRTIO_BALLOON_PFN_SHIFT 12
@@ -17,4 +18,20 @@ struct virtio_balloon_config
        /* Number of pages we've actually got in balloon. */
        __le32 actual;
 };
+
+#define VIRTIO_BALLOON_S_SWAP_IN  0   /* Number of pages swapped in */
+#define VIRTIO_BALLOON_S_SWAP_OUT 1   /* Number of pages swapped out */
+#define VIRTIO_BALLOON_S_ANON     2   /* Number of anonymous pages in use */
+#define VIRTIO_BALLOON_S_MAJFLT   3   /* Number of major faults */
+#define VIRTIO_BALLOON_S_MINFLT   4   /* Number of minor faults */
+#define VIRTIO_BALLOON_S_MEMFREE  5   /* Total amount of free memory */
+#define VIRTIO_BALLOON_S_MEMTOT   6   /* Total amount of memory */
+#define VIRTIO_BALLOON_S_NR       7
+
+struct virtio_balloon_stat
+{
+       __le16 tag;
+       __le32 val;
+};
+
 #endif /* _LINUX_VIRTIO_BALLOON_H */


-- 
Thanks,
Adam