total_rss_bytes and total_pss_bytes from smaps_rollup (#1134)

### What does this PR do?

This commit adds collection of total PSS bytes for all processes from
smaps_rollup, adjusting total_rss_bytes to also be from the same source

Author: blt

lading/src/observer/linux/procfs.rs

@@ -91,7 +91,7 @@ impl Sampler {
         let mut total_processes: u64 = 0;
         // We maintain a tally of the total RSS and PSS consumed by the parent
         // process and its children.
-        let mut total_rss: u64 = 0;
+        let mut aggr = memory::smaps_rollup::Aggregator::default();
 
         // Calculate the ticks since machine uptime. This will be important
         // later for calculating per-process uptime. Because we capture this one
@@ -270,7 +270,6 @@ impl Sampler {
             // Number of threads this process has active.
             gauge!("num_threads", &labels).set(stats.num_threads as f64);
 
-            total_rss += rss;
             total_processes += 1;
 
             // Also report memory data from `proc/status` as a reference point
@@ -358,7 +357,7 @@ impl Sampler {
                 }
 
                 // `/proc/{pid}/smaps_rollup`
-                if let Err(err) = memory::smaps_rollup::poll(pid, &labels).await {
+                if let Err(err) = memory::smaps_rollup::poll(pid, &labels, &mut aggr).await {
                     // We don't want to bail out entirely if we can't read smap rollup
                     // which will happen if we don't have permissions or, more
                     // likely, the process has exited.
@@ -420,7 +419,8 @@ impl Sampler {
 
         let totals = calculate_cpu_percentage(&total_sample, &self.previous_totals, self.num_cores);
 
-        gauge!("total_rss_bytes").set(total_rss as f64);
+        gauge!("total_rss_bytes").set(aggr.rss as f64);
+        gauge!("total_pss_bytes").set(aggr.pss as f64);
         gauge!("total_utime").set(total_sample.utime as f64);
         gauge!("total_stime").set(total_sample.stime as f64);
 

lading/src/observer/linux/procfs/memory/smaps_rollup.rs

@@ -16,8 +16,18 @@ pub(crate) enum Error {
     Parsing(String),
 }
 
+#[derive(Debug, Clone, Copy, Default)]
+pub(crate) struct Aggregator {
+    pub(crate) rss: u64,
+    pub(crate) pss: u64,
+}
+
 // Read `/proc/{pid}/smaps_rollup` and parse it directly into metrics.
-pub(crate) async fn poll(pid: i32, labels: &[(String, String)]) -> Result<(), Error> {
+pub(crate) async fn poll(
+    pid: i32,
+    labels: &[(String, String)],
+    aggr: &mut Aggregator,
+) -> Result<(), Error> {
     let path = format!("/proc/{pid}/smaps_rollup");
     // NOTE `read_to_string` uses as few IO operations as possible in its
     // implementation, so we might get the contents here in one go.
@@ -55,6 +65,11 @@ pub(crate) async fn poll(pid: i32, labels: &[(String, String)]) -> Result<(), Er
         let name_len = name.len();
         // Last character is a :, skip it.
         let field = name[..name_len - 1].to_snake_case();
+        match field.as_str() {
+            "rss" => aggr.rss += value_kb,
+            "pss" => aggr.pss += value_kb,
+            _ => { /* ignore other fields */ }
+        }
         let metric_name = format!("smaps_rollup.{field}");
         gauge!(metric_name, labels).set(value_kb as f64);
     }