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, 61 insertions, 37 deletions

diff --git a/monitor.c b/monitor.c
index be34329..fbae5ce 100644
--- a/monitor.c
+++ b/monitor.c
@@ -2152,33 +2152,13 @@ static void do_info_status(Monitor *mon, QObject **ret_data)
                                     vm_running, singlestep);
 }
 
-static ram_addr_t balloon_get_value(void)
+static void print_balloon_stat(const char *key, QObject *obj, void *opaque)
 {
-    ram_addr_t actual;
-
-    if (kvm_enabled() && !kvm_has_sync_mmu()) {
-        qemu_error_new(QERR_KVM_MISSING_CAP, "synchronous MMU", "balloon");
-        return 0;
-    }
-
-    actual = qemu_balloon_status();
-    if (actual == 0) {
-        qemu_error_new(QERR_DEVICE_NOT_ACTIVE, "balloon");
-        return 0;
-    }
-
-    return actual;
-}
+    Monitor *mon = opaque;
 
-/**
- * do_balloon(): Request VM to change its memory allocation
- */
-static void do_balloon(Monitor *mon, const QDict *qdict, QObject **ret_data)
-{
-    if (balloon_get_value()) {
-        /* ballooning is active */
-        qemu_balloon(qdict_get_int(qdict, "value"));
-    }
+    if (strcmp(key, "actual"))
+        monitor_printf(mon, ",%s=%" PRId64, key,
+                       qint_get_int(qobject_to_qint(obj)));
 }
 
 static void monitor_print_balloon(Monitor *mon, const QObject *data)
@@ -2186,31 +2166,74 @@ static void monitor_print_balloon(Monitor *mon, const QObject *data)
     QDict *qdict;
 
     qdict = qobject_to_qdict(data);
+    if (!qdict_haskey(qdict, "actual"))
+        return;
 
-    monitor_printf(mon, "balloon: actual=%" PRId64 "\n",
-                        qdict_get_int(qdict, "balloon") >> 20);
+    monitor_printf(mon, "balloon: actual=%" PRId64,
+                   qdict_get_int(qdict, "actual") >> 20);
+    qdict_iter(qdict, print_balloon_stat, mon);
+    monitor_printf(mon, "\n");
 }
 
 /**
  * do_info_balloon(): Balloon information
  *
- * Return a QDict with the following information:
+ * Make an asynchronous request for balloon info.  When the request completes
+ * a QDict will be returned according to the following specification:
  *
- * - "balloon": current balloon value in bytes
+ * - "actual": current balloon value in bytes
+ * The following fields may or may not be present:
+ * - "mem_swapped_in": Amount of memory swapped in (bytes)
+ * - "mem_swapped_out": Amount of memory swapped out (bytes)
+ * - "major_page_faults": Number of major faults
+ * - "minor_page_faults": Number of minor faults
+ * - "free_mem": Total amount of free and unused memory (bytes)
+ * - "total_mem": Total amount of available memory (bytes)
  *
  * Example:
  *
- * { "balloon": 1073741824 }
+ * { "actual": 1073741824, "mem_swapped_in": 0, "mem_swapped_out": 0,
+ *   "major_page_faults": 142, "minor_page_faults": 239245,
+ *   "free_mem": 1014185984, "total_mem": 1044668416 }
+ */
+static int do_info_balloon(Monitor *mon, MonitorCompletion cb, void *opaque)
+{
+    int ret;
+
+    if (kvm_enabled() && !kvm_has_sync_mmu()) {
+        qemu_error_new(QERR_KVM_MISSING_CAP, "synchronous MMU", "balloon");
+        return -1;
+    }
+
+    ret = qemu_balloon_status(cb, opaque);
+    if (!ret) {
+        qemu_error_new(QERR_DEVICE_NOT_ACTIVE, "balloon");
+        return -1;
+    }
+
+    return 0;
+}
+
+/**
+ * do_balloon(): Request VM to change its memory allocation
  */
-static void do_info_balloon(Monitor *mon, QObject **ret_data)
+static int do_balloon(Monitor *mon, const QDict *params,
+                       MonitorCompletion cb, void *opaque)
 {
-    ram_addr_t actual;
+    int ret;
+
+    if (kvm_enabled() && !kvm_has_sync_mmu()) {
+        qemu_error_new(QERR_KVM_MISSING_CAP, "synchronous MMU", "balloon");
+        return -1;
+    }
 
-    actual = balloon_get_value();
-    if (actual != 0) {
-        *ret_data = qobject_from_jsonf("{ 'balloon': %" PRId64 "}",
-                                       (int64_t) actual);
+    ret = qemu_balloon(qdict_get_int(params, "value"), cb, opaque);
+    if (ret == 0) {
+        qemu_error_new(QERR_DEVICE_NOT_ACTIVE, "balloon");
+        return -1;
     }
+
+    return 0;
 }
 
 static qemu_acl *find_acl(Monitor *mon, const char *name)
@@ -2696,7 +2719,8 @@ static const mon_cmd_t info_cmds[] = {
         .params     = "",
         .help       = "show balloon information",
         .user_print = monitor_print_balloon,
-        .mhandler.info_new = do_info_balloon,
+        .mhandler.info_async = do_info_balloon,
+        .async      = 1,
     },
     {
         .name       = "qtree",