virtio-balloon: add hugetlb page allocation counts

qemu should read and report hugetlb page allocation
counts exported in the following kernel patch:

    commit 4c3ca37c4a4394978fd0f005625f6064ed2b9a64
    Author: Jonathan Helman <jonathan.helman@oracle.com>
    Date:   Mon Mar 19 11:00:35 2018 -0700

    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>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Jason Wang <jasowang@redhat.com>

docs/virtio-balloon-stats.txt

@@ -34,6 +34,8 @@ which will return a dictionary containing:
       - stat-total-memory
       - stat-available-memory
       - stat-disk-caches
+      - stat-htlb-pgalloc
+      - stat-htlb-pgfail
 
   o A key named last-update, which contains the last stats update
     timestamp in seconds. Since this timestamp is generated by the host,

hw/virtio/virtio-balloon.c

@@ -52,6 +52,8 @@ static const char *balloon_stat_names[] = {
    [VIRTIO_BALLOON_S_MEMTOT] = "stat-total-memory",
    [VIRTIO_BALLOON_S_AVAIL] = "stat-available-memory",
    [VIRTIO_BALLOON_S_CACHES] = "stat-disk-caches",
+   [VIRTIO_BALLOON_S_HTLB_PGALLOC] = "stat-htlb-pgalloc",
+   [VIRTIO_BALLOON_S_HTLB_PGFAIL] = "stat-htlb-pgfail",
    [VIRTIO_BALLOON_S_NR] = NULL
 };
 

include/standard-headers/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.