virtio: Add memory statistics reporting to the balloon driver

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.

Signed-off-by: Adam Litke <agl@us.ibm.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

1 files changed, 14 insertions, 7 deletions

diff --git a/vl.c b/vl.c
index 5e8c775..1cd355c 100644
--- a/vl.c
+++ b/vl.c
@@ -365,17 +365,24 @@ void qemu_add_balloon_handler(QEMUBalloonEvent *func, void *opaque)
     qemu_balloon_event_opaque = opaque;
 }
 
-void qemu_balloon(ram_addr_t target)
+int qemu_balloon(ram_addr_t target, MonitorCompletion cb, void *opaque)
 {
-    if (qemu_balloon_event)
-        qemu_balloon_event(qemu_balloon_event_opaque, target);
+    if (qemu_balloon_event) {
+        qemu_balloon_event(qemu_balloon_event_opaque, target, cb, opaque);
+        return 1;
+    } else {
+        return 0;
+    }
 }
 
-ram_addr_t qemu_balloon_status(void)
+int qemu_balloon_status(MonitorCompletion cb, void *opaque)
 {
-    if (qemu_balloon_event)
-        return qemu_balloon_event(qemu_balloon_event_opaque, 0);
-    return 0;
+    if (qemu_balloon_event) {
+        qemu_balloon_event(qemu_balloon_event_opaque, 0, cb, opaque);
+        return 1;
+    } else {
+        return 0;
+    }
 }