virtio: Add memory statistics reporting to the balloon driver (V4)

Changes since V3:
 - Do not do endian conversions as they will be done in the host
 - Report stats that reference a quantity of memory in bytes
 - Minor coding style updates

Changes since V2:
 - Increase stat field size to 64 bits
 - Report all sizes in kb (not pages)
 - Drop anon_pages stat and fix endianness conversion

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 <agl@us.ibm.com>
Cc: Anthony Liguori <anthony@codemonkey.ws>
Cc: virtualization@lists.linux-foundation.org
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> (minor fixes)

1 files changed, 86 insertions, 8 deletions

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 505be88c82ae..cd778b1752b5 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -28,7 +28,7 @@
 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;
@@ -49,6 +49,9 @@ 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[] = {
@@ -154,6 +157,62 @@ static void leak_balloon(struct virtio_balloon *vb, size_t num)
         }
 }
 
+static inline void update_stat(struct virtio_balloon *vb, int idx,
+                               u16 tag, u64 val)
+{
+        BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
+        vb->stats[idx].tag = tag;
+        vb->stats[idx].val = val;
+}
+
+#define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
+
+static void update_balloon_stats(struct virtio_balloon *vb)
+{
+        unsigned long events[NR_VM_EVENT_ITEMS];
+        struct sysinfo i;
+        int idx = 0;
+
+        all_vm_events(events);
+        si_meminfo(&i);
+
+        update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
+                                pages_to_bytes(events[PSWPIN]));
+        update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
+                                pages_to_bytes(events[PSWPOUT]));
+        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,
+                                pages_to_bytes(i.freeram));
+        update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
+                                pages_to_bytes(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;
@@ -204,10 +263,10 @@ 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) {
@@ -220,13 +279,29 @@ 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)) {
@@ -264,7 +339,10 @@ static void __devexit 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_driver = {
         .feature_table = features,