bug: fix cgroup v1 memory total using sentinel max as total

src/collection/memory/sysinfo.rs

@@ -4,6 +4,9 @@ use std::num::NonZeroU64;
 
 use crate::collection::{DataCollector, memory::MemData};
 
+#[cfg(target_os = "linux")]
+use crate::collection::linux::cgroups::CgroupMemLimit;
+
 #[inline]
 fn get_usage(used: u64, total: u64) -> Option<MemData> {
     NonZeroU64::new(total).map(|total_bytes| MemData {
@@ -12,6 +15,20 @@ fn get_usage(used: u64, total: u64) -> Option<MemData> {
     })
 }
 
+/// Resolves the total memory to report given an optional cgroup limit and the physical total.
+///
+/// cgroup v1 reports an "unlimited" limit as a very large value, which causes problems if taken
+/// literally. This function caps it to the minimum of the cgroup total or the actual total to
+/// avoid this problem.
+#[cfg(target_os = "linux")]
+#[inline]
+fn resolve_cgroup_total(limit: Option<&CgroupMemLimit>, base_total: u64) -> u64 {
+    match limit {
+        Some(CgroupMemLimit::Bytes(bytes)) => (*bytes).min(base_total),
+        Some(CgroupMemLimit::Max) | None => base_total,
+    }
+}
+
 /// Returns memory (RAM) usage using sysinfo.
 ///
 /// On Linux, this will take cgroup usage/limits into account.
@@ -20,19 +37,13 @@ pub(crate) fn get_ram_usage(collector: &DataCollector) -> Option<MemData> {
 
     cfg_select! {
         target_os = "linux" => {
-            use crate::collection::linux::cgroups;
-
             let base_used = sys.used_memory();
             let base_total = sys.total_memory();
 
             let (used, total) = match &collector.cgroup_memory_data.ram {
                 Some(cgroup_data) => {
                     let used = cgroup_data.used_bytes;
-                    let total = match cgroup_data.limit {
+                    let total = resolve_cgroup_total(cgroup_data.limit.as_ref(), base_total);
-                        Some(cgroups::CgroupMemLimit::Bytes(bytes)) => bytes,
-                        Some(cgroups::CgroupMemLimit::Max) => base_total,
-                        None => base_total,
-                    };
 
                     (used, total)
                 }
@@ -56,19 +67,13 @@ pub(crate) fn get_swap_usage(collector: &DataCollector) -> Option<MemData> {
 
     cfg_select! {
         target_os = "linux" => {
-            use crate::collection::linux::cgroups;
-
             let base_used = sys.used_swap();
             let base_total = sys.total_swap();
 
             let (used, total) = match &collector.cgroup_memory_data.swap {
                 Some(cgroup_data) => {
                     let used = cgroup_data.used_bytes;
-                    let total = match cgroup_data.limit {
+                    let total = resolve_cgroup_total(cgroup_data.limit.as_ref(), base_total);
-                        Some(cgroups::CgroupMemLimit::Bytes(bytes)) => bytes,
-                        Some(cgroups::CgroupMemLimit::Max) => base_total,
-                        None => base_total,
-                    };
 
                     (used, total)
                 }
@@ -101,3 +106,39 @@ pub(crate) fn get_cache_usage(sys: &sysinfo::System) -> Option<MemData> {
 
     get_usage(mem_used, mem_total)
 }
+
+#[cfg(test)]
+#[cfg(target_os = "linux")]
+mod linux_tests {
+    use super::*;
+
+    const BASE_TOTAL: u64 = 16 * 1024 * 1024 * 1024; // 16 GiB
+
+    /// Regression test for <https://github.com/ClementTsang/bottom/issues/2092>.
+    #[test]
+    fn cap_cgroup_v1_limits() {
+        let sentinel = u64::MAX;
+        assert_eq!(
+            resolve_cgroup_total(Some(&CgroupMemLimit::Bytes(sentinel)), BASE_TOTAL),
+            BASE_TOTAL
+        );
+    }
+
+    #[test]
+    fn legit_cgroup_limit_works() {
+        let limit = 4 * 1024 * 1024 * 1024; // 4 GiB
+        assert_eq!(
+            resolve_cgroup_total(Some(&CgroupMemLimit::Bytes(limit)), BASE_TOTAL),
+            limit
+        );
+    }
+
+    #[test]
+    fn max_and_missing_limit_use_physical_total() {
+        assert_eq!(
+            resolve_cgroup_total(Some(&CgroupMemLimit::Max), BASE_TOTAL),
+            BASE_TOTAL
+        );
+        assert_eq!(resolve_cgroup_total(None, BASE_TOTAL), BASE_TOTAL);
+    }
+}