Move cgroup limits computation into its own function to split it out from the "normal" memory values

src/common.rs

@@ -458,6 +458,9 @@ impl System {
     /// let s = System::new_all();
     /// println!("{} bytes", s.total_memory());
     /// ```
+    ///
+    /// On Linux, if you want to see this information with the limit of your cgroup, take a look
+    /// at [`cgroup_limits`](System::cgroup_limits).
     pub fn total_memory(&self) -> u64 {
         self.inner.total_memory()
     }
@@ -546,6 +549,26 @@ impl System {
         self.inner.used_swap()
     }
 
+    /// Retrieves the limits for the current cgroup (if any), otherwise it returns `None`.
+    ///
+    /// This information is computed every time the method is called.
+    ///
+    /// ⚠️ You need to have run [`refresh_memory`](System::refresh_memory) at least once before
+    /// calling this method.
+    ///
+    /// ⚠️ This method is only implemented for Linux. It always returns `None` for all other
+    /// systems.
+    ///
+    /// ```no_run
+    /// use sysinfo::System;
+    ///
+    /// let s = System::new_all();
+    /// println!("limits: {:?}", s.cgroup_limits());
+    /// ```
+    pub fn cgroup_limits(&self) -> Option<CGroupLimits> {
+        self.inner.cgroup_limits()
+    }
+
     /// Returns system uptime (in seconds).
     ///
     /// ```no_run
@@ -2445,6 +2468,17 @@ impl std::fmt::Display for Signal {
     }
 }
 
+/// Contains memory limits for the current process.
+#[derive(Default, Debug, Clone)]
+pub struct CGroupLimits {
+    /// Total memory (in bytes) for the current cgroup.
+    pub total_memory: u64,
+    /// Free memory (in bytes) for the current cgroup.
+    pub free_memory: u64,
+    /// Free swap (in bytes) for the current cgroup.
+    pub free_swap: u64,
+}
+
 /// A struct representing system load average value.
 ///
 /// It is returned by [`System::load_average`][crate::System::load_average].

src/lib.rs

@@ -52,9 +52,9 @@ cfg_if::cfg_if! {
 }
 
 pub use crate::common::{
-    get_current_pid, Component, Components, Cpu, CpuRefreshKind, Disk, DiskKind, DiskUsage, Disks,
-    Gid, Group, LoadAvg, MacAddr, NetworkData, Networks, NetworksIter, Pid, Process,
-    ProcessRefreshKind, ProcessStatus, RefreshKind, Signal, System, Uid, User, Users,
+    get_current_pid, CGroupLimits, Component, Components, Cpu, CpuRefreshKind, Disk, DiskKind,
+    DiskUsage, Disks, Gid, Group, LoadAvg, MacAddr, NetworkData, Networks, NetworksIter, Pid,
+    Process, ProcessRefreshKind, ProcessStatus, RefreshKind, Signal, System, Uid, User, Users,
 };
 
 pub(crate) use crate::sys::{

src/serde.rs

@@ -134,6 +134,22 @@ impl serde::Serialize for crate::System {
     }
 }
 
+impl Serialize for crate::CGroupLimits {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        // `3` corresponds to the number of fields.
+        let mut state = serializer.serialize_struct("CGroupLimits", 3)?;
+
+        state.serialize_field("total_memory", &self.total_memory)?;
+        state.serialize_field("free_memory", &self.free_memory)?;
+        state.serialize_field("free_swap", &self.free_swap)?;
+
+        state.end()
+    }
+}
+
 impl Serialize for crate::Networks {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where

src/unix/apple/system.rs

@@ -159,6 +159,10 @@ impl SystemInner {
         }
     }
 
+    pub(crate) fn cgroup_limits(&self) -> Option<crate::CGroupLimits> {
+        None
+    }
+
     pub(crate) fn refresh_cpu_specifics(&mut self, refresh_kind: CpuRefreshKind) {
         self.cpus.refresh(refresh_kind, self.port);
     }

src/unix/freebsd/system.rs

@@ -55,6 +55,10 @@ impl SystemInner {
         self.swap_used = swap_used;
     }
 
+    pub(crate) fn cgroup_limits(&self) -> Option<crate::CGroupLimits> {
+        None
+    }
+
     pub(crate) fn refresh_cpu_specifics(&mut self, refresh_kind: CpuRefreshKind) {
         self.cpus.refresh(refresh_kind)
     }

src/unix/linux/system.rs

@@ -224,39 +224,10 @@ impl SystemInner {
                 .saturating_add(self.mem_slab_reclaimable)
                 .saturating_sub(self.mem_shmem);
         }
+    }
 
-        if let (Some(mem_cur), Some(mem_max)) = (
-            read_u64("/sys/fs/cgroup/memory.current"),
-            read_u64("/sys/fs/cgroup/memory.max"),
-        ) {
-            // cgroups v2
-            self.mem_total = min(mem_max, self.mem_total);
-            self.mem_free = self.mem_total.saturating_sub(mem_cur);
-            self.mem_available = self.mem_free;
-
-            if let Some(swap_cur) = read_u64("/sys/fs/cgroup/memory.swap.current") {
-                self.swap_free = self.swap_total.saturating_sub(swap_cur);
-            }
-
-            read_table("/sys/fs/cgroup/memory.stat", ' ', |key, value| {
-                let field = match key {
-                    "slab_reclaimable" => &mut self.mem_slab_reclaimable,
-                    "file" => &mut self.mem_page_cache,
-                    "shmem" => &mut self.mem_shmem,
-                    _ => return,
-                };
-                *field = value;
-                self.mem_free = self.mem_free.saturating_sub(value);
-            });
-        } else if let (Some(mem_cur), Some(mem_max)) = (
-            // cgroups v1
-            read_u64("/sys/fs/cgroup/memory/memory.usage_in_bytes"),
-            read_u64("/sys/fs/cgroup/memory/memory.limit_in_bytes"),
-        ) {
-            self.mem_total = min(mem_max, self.mem_total);
-            self.mem_free = self.mem_total.saturating_sub(mem_cur);
-            self.mem_available = self.mem_free;
-        }
+    pub(crate) fn cgroup_limits(&self) -> Option<crate::CGroupLimits> {
+        crate::CGroupLimits::new(self)
     }
 
     pub(crate) fn refresh_cpu_specifics(&mut self, refresh_kind: CpuRefreshKind) {
@@ -536,6 +507,57 @@ where
     }
 }
 
+impl crate::CGroupLimits {
+    fn new(sys: &SystemInner) -> Option<Self> {
+        assert!(
+            sys.mem_total != 0,
+            "You need to call System::refresh_memory before trying to get cgroup limits!",
+        );
+        if let (Some(mem_cur), Some(mem_max)) = (
+            read_u64("/sys/fs/cgroup/memory.current"),
+            read_u64("/sys/fs/cgroup/memory.max"),
+        ) {
+            // cgroups v2
+
+            let mut limits = Self {
+                total_memory: sys.mem_total,
+                free_memory: sys.mem_free,
+                free_swap: sys.swap_free,
+            };
+
+            limits.total_memory = min(mem_max, sys.mem_total);
+            limits.free_memory = limits.total_memory.saturating_sub(mem_cur);
+
+            if let Some(swap_cur) = read_u64("/sys/fs/cgroup/memory.swap.current") {
+                limits.free_swap = sys.swap_total.saturating_sub(swap_cur);
+            }
+
+            read_table("/sys/fs/cgroup/memory.stat", ' ', |_key, value| {
+                limits.free_memory = limits.free_memory.saturating_sub(value);
+            });
+
+            Some(limits)
+        } else if let (Some(mem_cur), Some(mem_max)) = (
+            // cgroups v1
+            read_u64("/sys/fs/cgroup/memory/memory.usage_in_bytes"),
+            read_u64("/sys/fs/cgroup/memory/memory.limit_in_bytes"),
+        ) {
+            let mut limits = Self {
+                total_memory: sys.mem_total,
+                free_memory: sys.mem_free,
+                free_swap: sys.swap_free,
+            };
+
+            limits.total_memory = min(mem_max, sys.mem_total);
+            limits.free_memory = limits.total_memory.saturating_sub(mem_cur);
+
+            Some(limits)
+        } else {
+            None
+        }
+    }
+}
+
 #[derive(PartialEq, Eq)]
 enum InfoType {
     /// The end-user friendly name of:

src/unknown/system.rs

@@ -21,6 +21,10 @@ impl SystemInner {
 
     pub(crate) fn refresh_memory(&mut self) {}
 
+    pub(crate) fn cgroup_limits(&self) -> Option<crate::CGroupLimits> {
+        None
+    }
+
     pub(crate) fn refresh_cpu_specifics(&mut self, _refresh_kind: CpuRefreshKind) {}
 
     pub(crate) fn refresh_processes_specifics(&mut self, _refresh_kind: ProcessRefreshKind) {}

src/windows/system.rs

@@ -165,6 +165,10 @@ impl SystemInner {
         }
     }
 
+    pub(crate) fn cgroup_limits(&self) -> Option<crate::CGroupLimits> {
+        None
+    }
+
     #[allow(clippy::map_entry)]
     pub(crate) fn refresh_process_specifics(
         &mut self,