virtio_balloon: export hugetlb page allocation counts

Export the number of successful and failed hugetlb page
allocations via the virtio balloon driver. These 2 counts
come directly from the vm_events HTLB_BUDDY_PGALLOC and
HTLB_BUDDY_PGALLOC_FAIL.
Signed-off-by: Jonathan Helman <jonathan.helman@oracle.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Jason Wang <jasowang@redhat.com>

drivers/virtio/virtio_balloon.c

@@ -272,6 +272,12 @@ static unsigned int update_balloon_stats(struct virtio_balloon *vb)
 				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]);
+#ifdef CONFIG_HUGETLB_PAGE
+	update_stat(vb, idx++, VIRTIO_BALLOON_S_HTLB_PGALLOC,
+		    events[HTLB_BUDDY_PGALLOC]);
+	update_stat(vb, idx++, VIRTIO_BALLOON_S_HTLB_PGFAIL,
+		    events[HTLB_BUDDY_PGALLOC_FAIL]);
+#endif
 #endif
 	update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
 				pages_to_bytes(i.freeram));

include/uapi/linux/virtio_balloon.h

@@ -53,7 +53,9 @@ struct virtio_balloon_config {
 #define VIRTIO_BALLOON_S_MEMTOT   5   /* Total amount of memory */
 #define VIRTIO_BALLOON_S_AVAIL    6   /* Available memory as in /proc */
 #define VIRTIO_BALLOON_S_CACHES   7   /* Disk caches */
-#define VIRTIO_BALLOON_S_NR       8
+#define VIRTIO_BALLOON_S_HTLB_PGALLOC  8  /* Hugetlb page allocations */
+#define VIRTIO_BALLOON_S_HTLB_PGFAIL   9  /* Hugetlb page allocation failures */
+#define VIRTIO_BALLOON_S_NR       10
 
 /*
  * Memory statistics structure.