feat: expose locked memory in pageserver /metrics (#6669)

context: https://github.com/neondatabase/neon/issues/6667

Cargo.lock

@@ -2869,6 +2869,7 @@ dependencies = [
  "chrono",
  "libc",
  "once_cell",
+ "procfs",
  "prometheus",
  "rand 0.8.5",
  "rand_distr",
@@ -3986,6 +3987,8 @@ checksum = "b1de8dacb0873f77e6aefc6d71e044761fcc68060290f5b1089fcdf84626bb69"
 dependencies = [
  "bitflags 1.3.2",
  "byteorder",
+ "chrono",
+ "flate2",
  "hex",
  "lazy_static",
  "rustix 0.36.16",

Cargo.toml

@@ -113,6 +113,7 @@ parquet = { version = "49.0.0", default-features = false, features = ["zstd"] }
 parquet_derive = "49.0.0"
 pbkdf2 = { version = "0.12.1", features = ["simple", "std"] }
 pin-project-lite = "0.2"
+procfs = "0.14"
 prometheus = {version = "0.13", default_features=false, features = ["process"]} # removes protobuf dependency
 prost = "0.11"
 rand = "0.8"

libs/metrics/Cargo.toml

@@ -13,6 +13,9 @@ twox-hash.workspace = true
 
 workspace_hack.workspace = true
 
+[target.'cfg(target_os = "linux")'.dependencies]
+procfs.workspace = true
+
 [dev-dependencies]
 rand = "0.8"
 rand_distr = "0.4.3"

libs/metrics/src/lib.rs

@@ -31,6 +31,8 @@ pub use wrappers::{CountedReader, CountedWriter};
 mod hll;
 pub mod metric_vec_duration;
 pub use hll::{HyperLogLog, HyperLogLogVec};
+#[cfg(target_os = "linux")]
+pub mod more_process_metrics;
 
 pub type UIntGauge = GenericGauge<AtomicU64>;
 pub type UIntGaugeVec = GenericGaugeVec<AtomicU64>;

libs/metrics/src/more_process_metrics.rs

@@ -0,0 +1,54 @@
+//! process metrics that the [`::prometheus`] crate doesn't provide.
+
+// This module has heavy inspiration from the prometheus crate's `process_collector.rs`.
+
+use crate::UIntGauge;
+
+pub struct Collector {
+    descs: Vec<prometheus::core::Desc>,
+    vmlck: crate::UIntGauge,
+}
+
+const NMETRICS: usize = 1;
+
+impl prometheus::core::Collector for Collector {
+    fn desc(&self) -> Vec<&prometheus::core::Desc> {
+        self.descs.iter().collect()
+    }
+
+    fn collect(&self) -> Vec<prometheus::proto::MetricFamily> {
+        let Ok(myself) = procfs::process::Process::myself() else {
+            return vec![];
+        };
+        let mut mfs = Vec::with_capacity(NMETRICS);
+        if let Ok(status) = myself.status() {
+            if let Some(vmlck) = status.vmlck {
+                self.vmlck.set(vmlck);
+                mfs.extend(self.vmlck.collect())
+            }
+        }
+        mfs
+    }
+}
+
+impl Collector {
+    pub fn new() -> Self {
+        let mut descs = Vec::new();
+
+        let vmlck =
+            UIntGauge::new("libmetrics_process_status_vmlck", "/proc/self/status vmlck").unwrap();
+        descs.extend(
+            prometheus::core::Collector::desc(&vmlck)
+                .into_iter()
+                .cloned(),
+        );
+
+        Self { descs, vmlck }
+    }
+}
+
+impl Default for Collector {
+    fn default() -> Self {
+        Self::new()
+    }
+}

pageserver/src/bin/pageserver.rs

@@ -272,6 +272,8 @@ fn start_pageserver(
     );
     set_build_info_metric(GIT_VERSION, BUILD_TAG);
     set_launch_timestamp_metric(launch_ts);
+    #[cfg(target_os = "linux")]
+    metrics::register_internal(Box::new(metrics::more_process_metrics::Collector::new())).unwrap();
     pageserver::preinitialize_metrics();
 
     // If any failpoints were set from FAILPOINTS environment variable,