virtio-balloon: Add metrics for hinting/reporting

Add metrics to track free page hinting and reporting. For both devices
track the number of ranges reported, the number of errors encountered
while freeing and the total amount of memory freed.

Signed-off-by: Jack Thomson <jackabt@amazon.com>

Author: JackThomson2

src/vmm/src/devices/virtio/balloon/device.rs

@@ -549,8 +549,12 @@ impl Balloon {
                     continue;
                 }
 
+                METRICS.free_page_hint_count.inc();
                 if let Err(err) = mem.discard_range(desc.addr, desc.len as usize) {
+                    METRICS.free_page_hint_fails.inc();
                     error!("balloon hinting: failed to remove range: {err:?}");
+                } else {
+                    METRICS.free_page_hint_freed.add(desc.len as u64);
                 }
             }
 
@@ -587,8 +591,12 @@ impl Balloon {
 
             let mut last_desc = Some(head);
             while let Some(desc) = last_desc {
+                METRICS.free_page_report_count.inc();
                 if let Err(err) = mem.discard_range(desc.addr, desc.len as usize) {
+                    METRICS.free_page_report_fails.inc();
                     error!("balloon: failed to remove range: {err:?}");
+                } else {
+                    METRICS.free_page_report_freed.add(desc.len as u64);
                 }
                 last_desc = desc.next_descriptor();
             }

src/vmm/src/devices/virtio/balloon/metrics.rs

@@ -63,6 +63,18 @@ pub(super) struct BalloonDeviceMetrics {
     pub deflate_count: SharedIncMetric,
     /// Number of times when handling events on a balloon device failed.
     pub event_fails: SharedIncMetric,
+    /// Number of times when free page repoting was triggered
+    pub free_page_report_count: SharedIncMetric,
+    /// Total memory freed by the reporting driver
+    pub free_page_report_freed: SharedIncMetric,
+    /// Number of errors occurred while reporting
+    pub free_page_report_fails: SharedIncMetric,
+    /// Number of times when free page hinting was triggered
+    pub free_page_hint_count: SharedIncMetric,
+    /// Total memory freed by the hinting driver
+    pub free_page_hint_freed: SharedIncMetric,
+    /// Number of errors occurred while hinting
+    pub free_page_hint_fails: SharedIncMetric,
 }
 impl BalloonDeviceMetrics {
     /// Const default construction.
@@ -74,6 +86,12 @@ impl BalloonDeviceMetrics {
             stats_update_fails: SharedIncMetric::new(),
             deflate_count: SharedIncMetric::new(),
             event_fails: SharedIncMetric::new(),
+            free_page_report_count: SharedIncMetric::new(),
+            free_page_report_freed: SharedIncMetric::new(),
+            free_page_report_fails: SharedIncMetric::new(),
+            free_page_hint_count: SharedIncMetric::new(),
+            free_page_hint_freed: SharedIncMetric::new(),
+            free_page_hint_fails: SharedIncMetric::new(),
         }
     }
 }

tests/host_tools/fcmetrics.py

@@ -140,6 +140,12 @@ def validate_fc_metrics(metrics):
             "stats_update_fails",
             "deflate_count",
             "event_fails",
+            "free_page_report_count",
+            "free_page_report_freed",
+            "free_page_report_fails",
+            "free_page_hint_count",
+            "free_page_hint_freed",
+            "free_page_hint_fails",
         ],
         "block": block_metrics,
         "deprecated_api": [