[PATCH v3] virtio_balloon: include disk/file caches memory statistics

[Tomáš Golembiovský <tgolembi@redhat.com>]

Add a new field VIRTIO_BALLOON_S_CACHES to virtio_balloon memory
statistics protocol. The value represents all disk/file caches.

In this case it corresponds to the sum of values
Buffers+Cached+SwapCached from /proc/meminfo.

Signed-off-by: Tomáš Golembiovský <tgolembi@redhat.com>
---
 drivers/virtio/virtio_balloon.c     | 4 ++++
 include/uapi/linux/virtio_balloon.h | 3 ++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index f0b3a0b9d42f..d2bd13bbaf9f 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -244,11 +244,13 @@ static unsigned int update_balloon_stats(struct virtio_balloon *vb)
 	struct sysinfo i;
 	unsigned int idx = 0;
 	long available;
+	unsigned long caches;
 
 	all_vm_events(events);
 	si_meminfo(&i);
 
 	available = si_mem_available();
+	caches = global_node_page_state(NR_FILE_PAGES);
 
 #ifdef CONFIG_VM_EVENT_COUNTERS
 	update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
@@ -264,6 +266,8 @@ static unsigned int update_balloon_stats(struct virtio_balloon *vb)
 				pages_to_bytes(i.totalram));
 	update_stat(vb, idx++, VIRTIO_BALLOON_S_AVAIL,
 				pages_to_bytes(available));
+	update_stat(vb, idx++, VIRTIO_BALLOON_S_CACHES,
+				pages_to_bytes(caches));
 
 	return idx;
 }
diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
index 343d7ddefe04..4e8b8304b793 100644
--- a/include/uapi/linux/virtio_balloon.h
+++ b/include/uapi/linux/virtio_balloon.h
@@ -52,7 +52,8 @@ struct virtio_balloon_config {
 #define VIRTIO_BALLOON_S_MEMFREE  4   /* Total amount of free memory */
 #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_NR       7
+#define VIRTIO_BALLOON_S_CACHES   7   /* Disk caches */
+#define VIRTIO_BALLOON_S_NR       8
 
 /*
  * Memory statistics structure.
-- 
2.15.0