Emit malloc metrics

mountpoint-s3/src/cli.rs

@@ -581,12 +581,25 @@ impl CliArgs {
     }
 }
 
+#[cfg(target_os = "linux")]
+fn configure_malloc() {
+    unsafe {
+        // Disable dynamic MMAP_THRESHOLD and set it to 4MiB: https://github.com/bminor/glibc/blob/release/2.26/master/malloc/malloc.c#L1739
+
+        // NOTE: M_MMAP_MAX is 65536. With 8MiB allocations it allows up to 512GiB of simultaneously allocated memory via mmap, which should fit for most of the cases. For more info:
+        // https://github.com/bminor/glibc/blob/release/2.26/master/malloc/malloc.c#L983
+        libc::mallopt(libc::M_MMAP_THRESHOLD, 4194304);
+    }
+}
+
 pub fn main<ClientBuilder, Client, Runtime>(client_builder: ClientBuilder) -> anyhow::Result<()>
 where
     ClientBuilder: FnOnce(&CliArgs) -> anyhow::Result<(Client, Runtime, S3Personality)>,
     Client: ObjectClient + Clone + Send + Sync + 'static,
     Runtime: Spawn + Clone + Send + Sync + 'static,
 {
+    #[cfg(target_os = "linux")]
+    configure_malloc();
     let args = CliArgs::parse();
     let successful_mount_msg = format!(
         "{} is mounted at {}",

mountpoint-s3/src/metrics.rs

@@ -44,6 +44,8 @@ pub fn install() -> MetricsSinkHandle {
                     Ok(()) | Err(RecvTimeoutError::Disconnected) => break,
                     Err(RecvTimeoutError::Timeout) => {
                         poll_process_metrics(&mut sys);
+                        #[cfg(target_os = "linux")]
+                        poll_malloc_metrics();
                         inner.publish()
                     }
                 }
@@ -52,6 +54,8 @@ pub fn install() -> MetricsSinkHandle {
             // any new metrics data after the sink shuts down, but we assume a clean shutdown
             // stops generating new metrics before shutting down the sink.
             poll_process_metrics(&mut sys);
+            #[cfg(target_os = "linux")]
+            poll_malloc_metrics();
             inner.publish();
         })
     };
@@ -87,6 +91,25 @@ fn poll_process_metrics(sys: &mut System) {
     }
 }
 
+#[cfg(target_os = "linux")]
+fn poll_malloc_metrics() {
+    unsafe {
+        let mallinfo = libc::mallinfo();
+        // Space wasted due to fragmentation: `process.mallinfo.arena - process.mallinfo.fordblks`
+        metrics::gauge!("process.mallinfo.arena").set(mallinfo.arena as f64); /* non-mmapped space allocated from system */
+        metrics::gauge!("process.mallinfo.ordblks").set(mallinfo.ordblks as f64); /* number of free chunks */
+        metrics::gauge!("process.mallinfo.smblks").set(mallinfo.smblks as f64); /* number of fastbin blocks */
+        metrics::gauge!("process.mallinfo.hblks").set(mallinfo.hblks as f64); /* number of mmapped regions */
+        metrics::gauge!("process.mallinfo.hblkhd").set(mallinfo.hblkhd as f64); /* space in mmapped regions */
+        metrics::gauge!("process.mallinfo.usmblks").set(mallinfo.usmblks as f64); /* always 0, preserved for backwards compatibility */
+        metrics::gauge!("process.mallinfo.fsmblks").set(mallinfo.fsmblks as f64); /* space available in freed fastbin blocks */
+        metrics::gauge!("process.mallinfo.uordblks").set(mallinfo.uordblks as f64); /* total allocated space */
+        metrics::gauge!("process.mallinfo.fordblks").set(mallinfo.fordblks as f64); /* total free space */
+        /* top-most, releasable (via malloc_trim) space */
+        metrics::gauge!("process.mallinfo.keepcost").set(mallinfo.keepcost as f64);
+    }
+}
+
 #[derive(Debug)]
 struct MetricsSink {
     metrics: DashMap<Key, Metric>,