start_command/
cgroup_memory.rs

1//! cgroup v2 memory counters of a detached docker container (issue #182).
2//!
3//! Docker's `State.OOMKilled` is container-wide and sticky (moby/moby#43564):
4//! it says that *some* process in the container was OOM-killed at some point,
5//! but not how many, not whether the container hit its own `--memory` limit or
6//! the whole host ran out, and not how close the execution came to its limit.
7//! The kernel provides raw counters per cgroup
8//! (<https://docs.kernel.org/admin-guide/cgroup-v2.html#memory-interface-files>):
9//!
10//! ```text
11//! memory.events `oom`       allocation events reaching the memory limit
12//! memory.events `oom_kill`  processes killed here by *any* OOM killer
13//! memory.peak / memory.max  peak usage (Linux 5.19+) and limit (`max` when
14//!                           unlimited)
15//! ```
16//! These counters have different units and are hierarchical. A group OOM can
17//! kill several processes for one allocation event; earlier allocation events
18//! can also coexist with a later host OOM. Their comparison cannot establish
19//! container, parent or host scope (issue #185).
20//!
21//! The cgroup is removed when the container stops, so the values cannot be read
22//! afterwards. The detached completion watcher therefore samples them while the
23//! container runs and hands the last sample to the post-mortem, the finalizer
24//! and the recovery step. Best effort by design: no cgroup v2, a remote docker
25//! daemon or a hidden `/proc` leave the counters unknown, and a kill in the last
26//! sampling interval can be missed when the cgroup is gone before the final
27//! read.
28
29use serde::{Deserialize, Deserializer, Serialize};
30use serde_json::Value;
31
32use crate::isolation::isolation_log::shell_quote;
33
34/// Seconds between two samples of a running container's cgroup.
35pub const CGROUP_SAMPLE_INTERVAL_SECONDS: u64 = 1;
36
37/// Shell variables used by the sampler snippets.
38pub mod cgroup_shell_vars {
39    /// Last sample: `<memory.max> <memory.peak> <oom> <oom_kill>`.
40    pub const SAMPLE: &str = "__start_command_cgroup";
41    pub const SAMPLER: &str = "__start_command_cgroup_sampler";
42    pub const FILE: &str = "__start_command_cgroup_file";
43}
44
45/// Where the OOM killer that killed processes in the container came from.
46#[derive(Debug, Clone, Copy, PartialEq, Eq)]
47pub enum OomScope {
48    /// Raw counters do not establish container, parent or host scope.
49    Unknown,
50    /// Retained scope name; raw counters alone cannot establish it.
51    ContainerLimit,
52    /// Retained scope name; raw counters alone cannot establish it.
53    HostOrParent,
54}
55
56impl OomScope {
57    pub fn as_str(&self) -> &'static str {
58        match self {
59            OomScope::Unknown => "unknown",
60            OomScope::ContainerLimit => "container-limit",
61            OomScope::HostOrParent => "host-or-parent",
62        }
63    }
64
65    pub fn note(&self) -> &'static str {
66        match self {
67            OomScope::Unknown => "OOM kill scope unknown",
68            OomScope::ContainerLimit => "the container hit its own memory limit",
69            OomScope::HostOrParent => "a host-wide or parent cgroup OOM killed processes here",
70        }
71    }
72}
73
74/// The counters of one sample. `limit_bytes` is `None` without a limit.
75#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Serialize, Deserialize)]
76#[serde(rename_all = "camelCase")]
77pub struct CgroupMemory {
78    pub limit_bytes: Option<u64>,
79    pub peak_bytes: Option<u64>,
80    pub oom_events: Option<u64>,
81    pub oom_kills: Option<u64>,
82}
83
84/// Shell functions shared by the sampler and its final read:
85///
86/// ```text
87/// __start_command_cgroup_dir NAME  print the container's cgroup v2 directory
88/// __start_command_cgroup_read DIR  print `<max> <peak> <oom> <oom_kill> DIR`
89/// ```
90///
91/// The directory comes from `/proc/<.State.Pid>/cgroup` (`0::<path>`), which
92/// covers the systemd and cgroupfs drivers, `--cgroup-parent` and rootless
93/// docker alike; the two default layouts are fallbacks. A candidate must name
94/// the container ID, so a PID reported by a remote daemon can never select an
95/// unrelated local cgroup. `START_COMMAND_CGROUP_ROOT` and
96/// `START_COMMAND_PROC_ROOT` replace `/sys/fs/cgroup` and `/proc` (tests).
97pub fn build_cgroup_functions_snippet() -> String {
98    [
99        concat!(
100            "__start_command_cgroup_dir() { __scd_id=$(docker inspect -f '{{.Id}}' \"$1\" 2>/dev/null); ",
101            "[ -n \"$__scd_id\" ] || return 1; ",
102            "__scd_pid=$(docker inspect -f '{{.State.Pid}}' \"$1\" 2>/dev/null); __scd_rel=''; ",
103            "case \"$__scd_pid\" in ''|0|*[!0-9]*) ;; ",
104            "*) __scd_rel=$(sed -n 's/^0:://p' \"${START_COMMAND_PROC_ROOT:-/proc}/$__scd_pid/cgroup\" 2>/dev/null);; esac; ",
105            "__scd_root=${START_COMMAND_CGROUP_ROOT:-/sys/fs/cgroup}; ",
106            "for __scd_dir in ${__scd_rel:+\"$__scd_root$__scd_rel\"} ",
107            "\"$__scd_root/system.slice/docker-$__scd_id.scope\" \"$__scd_root/docker/$__scd_id\"; do ",
108            "case \"$__scd_dir\" in *\"$__scd_id\"*) if [ -r \"$__scd_dir/memory.events\" ]; then ",
109            "printf '%s' \"$__scd_dir\"; return 0; fi;; esac; done; return 1; }",
110        ),
111        concat!(
112            "__start_command_cgroup_read() { __scr_events=$(cat \"$1/memory.events\" 2>/dev/null) || return 1; ",
113            "__scr_oom=$(printf '%s\\n' \"$__scr_events\" | sed -n 's/^oom //p'); ",
114            "__scr_kill=$(printf '%s\\n' \"$__scr_events\" | sed -n 's/^oom_kill //p'); ",
115            "__scr_max=$(cat \"$1/memory.max\" 2>/dev/null); __scr_peak=$(cat \"$1/memory.peak\" 2>/dev/null); ",
116            "printf '%s %s %s %s %s\\n' \"${__scr_max:--}\" \"${__scr_peak:--}\" ",
117            "\"${__scr_oom:--}\" \"${__scr_kill:--}\" \"$1\"; }",
118        ),
119    ]
120    .join("; ")
121}
122
123/// Shell fragment starting the background sampler. It writes each sample to a
124/// temp file with `mv`, so the watcher never reads a half-written line, and
125/// ends by itself once the cgroup is gone.
126pub fn build_cgroup_sampler_start_snippet(container_name: &str) -> String {
127    use cgroup_shell_vars::{FILE, SAMPLER};
128    [
129        build_cgroup_functions_snippet(),
130        format!("{}=\"${{TMPDIR:-/tmp}}/start-command-cgroup.$$\"", FILE),
131        format!("rm -f \"${f}\" \"${f}.tmp\"", f = FILE),
132        format!(
133            "( __scs_dir=$(__start_command_cgroup_dir {name}) || exit 0; \
134             while __scs_line=$(__start_command_cgroup_read \"$__scs_dir\"); do \
135             printf '%s\\n' \"$__scs_line\" > \"${f}.tmp\" && mv -f \"${f}.tmp\" \"${f}\"; \
136             sleep {interval}; done ) >/dev/null 2>&1 & {sampler}=$!",
137            name = shell_quote(container_name),
138            f = FILE,
139            interval = CGROUP_SAMPLE_INTERVAL_SECONDS,
140            sampler = SAMPLER,
141        ),
142    ]
143    .join("; ")
144}
145
146/// Shell fragment stopping the sampler once the container has exited and
147/// leaving the last sample (`<max> <peak> <oom> <oom_kill>`, or empty) in
148/// `$__start_command_cgroup`. The cgroup can outlive the main process for a
149/// moment, so it is read one last time when it still exists.
150pub fn build_cgroup_sampler_stop_snippet() -> String {
151    use cgroup_shell_vars::{FILE, SAMPLE, SAMPLER};
152    [
153        format!("kill \"${}\" 2>/dev/null", SAMPLER),
154        format!("wait \"${}\" 2>/dev/null", SAMPLER),
155        format!("{}=$(cat \"${}\" 2>/dev/null)", SAMPLE, FILE),
156        format!("__scs_dir=$(printf '%s' \"${}\" | cut -s -d ' ' -f 5-)", SAMPLE),
157        format!(
158            "if [ -n \"$__scs_dir\" ] && __scs_line=$(__start_command_cgroup_read \"$__scs_dir\"); then {}=$__scs_line; fi",
159            SAMPLE
160        ),
161        format!("rm -f \"${f}\" \"${f}.tmp\"", f = FILE),
162        format!(
163            "{s}=$(printf '%s' \"${s}\" | cut -d ' ' -f 1-4)",
164            s = SAMPLE
165        ),
166    ]
167    .join("; ")
168}
169
170/// Shell fragment appending the `Memory:` line of the post-mortem when a
171/// sample exists. `quoted_log_path` must already be shell-quoted.
172pub fn build_cgroup_memory_log_snippet(quoted_log_path: &str) -> String {
173    let sample = cgroup_shell_vars::SAMPLE;
174    // A function, so `$1`.. of the watcher script itself stay untouched.
175    format!(
176        "__start_command_cgroup_log() {{ __scm_note=''; \
177         if [ \"$4\" -gt 0 ] 2>/dev/null; then __scm_note=' ({unknown})'; fi; \
178         printf 'Memory:     memory.max=%s memory.peak=%s oom=%s oom_kill=%s%s\\n' \
179         \"$1\" \"$2\" \"$3\" \"$4\" \"$__scm_note\"; }}; \
180         if [ -n \"${sample}\" ]; then __start_command_cgroup_log ${sample} >> {log}; fi",
181        unknown = OomScope::Unknown.note(),
182        sample = sample,
183        log = quoted_log_path,
184    )
185}
186
187fn parse_counter(text: &str) -> Option<u64> {
188    if !text.is_empty() && text.chars().all(|c| c.is_ascii_digit()) {
189        text.parse().ok()
190    } else {
191        None
192    }
193}
194
195/// Parse a sample written by the watcher
196/// (`<memory.max> <memory.peak> <oom> <oom_kill>`); `None` without a sample.
197pub fn parse_cgroup_memory_sample(text: &str) -> Option<CgroupMemory> {
198    let fields: Vec<&str> = text.split_whitespace().collect();
199    if fields.len() < 4 {
200        return None;
201    }
202    let counters = CgroupMemory {
203        limit_bytes: parse_counter(fields[0]),
204        peak_bytes: parse_counter(fields[1]),
205        oom_events: parse_counter(fields[2]),
206        oom_kills: parse_counter(fields[3]),
207    };
208    if counters.oom_events.is_none() && counters.oom_kills.is_none() {
209        // memory.events was unreadable: the line carries no information.
210        return None;
211    }
212    Some(counters)
213}
214
215/// The `Memory:` line for a sample, exactly as the watcher's shell writes it.
216/// Used where Rust writes the post-mortem itself (the recovery step).
217pub fn format_cgroup_memory_log_line(text: &str) -> Option<String> {
218    let counters = parse_cgroup_memory_sample(text)?;
219    let fields: Vec<&str> = text.split_whitespace().collect();
220    let note = describe_cgroup_oom_scope(&counters)
221        .map(|scope| format!(" ({})", scope.note()))
222        .unwrap_or_default();
223    Some(format!(
224        "Memory:     memory.max={} memory.peak={} oom={} oom_kill={}{}",
225        fields[0], fields[1], fields[2], fields[3], note
226    ))
227}
228
229/// `Unknown` for observed kills, `None` when no kills were observed.
230///
231/// Separately attributed kernel/cgroup evidence would be needed to establish
232/// container, parent or host scope. An unknown `oom_events` remains unknown.
233pub fn describe_cgroup_oom_scope(memory: &CgroupMemory) -> Option<OomScope> {
234    memory.oom_kills.filter(|kills| *kills > 0)?;
235    Some(OomScope::Unknown)
236}
237
238fn format_bytes(bytes: Option<u64>) -> String {
239    let Some(bytes) = bytes else {
240        return "unknown".to_string();
241    };
242    const UNITS: [&str; 5] = ["B", "KiB", "MiB", "GiB", "TiB"];
243    let mut value = bytes as f64;
244    let mut unit = 0;
245    while value >= 1024.0 && unit < UNITS.len() - 1 {
246        value /= 1024.0;
247        unit += 1;
248    }
249    if unit == 0 {
250        format!("{} B", bytes)
251    } else {
252        format!("{:.1} {}", value, UNITS[unit])
253    }
254}
255
256/// Human-readable counters for `--status`, e.g.
257/// `peak 255.9 MiB of 256.0 MiB limit, oom 0, oom_kill 3 (...)`.
258pub fn format_cgroup_memory(memory: &CgroupMemory) -> String {
259    let limit = match memory.limit_bytes {
260        Some(_) => format!("{} limit", format_bytes(memory.limit_bytes)),
261        None => "no limit".to_string(),
262    };
263    let count = |value: Option<u64>| value.map_or_else(|| "unknown".to_string(), |v| v.to_string());
264    let note = describe_cgroup_oom_scope(memory)
265        .map(|scope| format!(" ({})", scope.note()))
266        .unwrap_or_default();
267    format!(
268        "peak {} of {}, oom {}, oom_kill {}{}",
269        format_bytes(memory.peak_bytes),
270        limit,
271        count(memory.oom_events),
272        count(memory.oom_kills),
273        note
274    )
275}
276
277fn counter_from_value(value: Option<&Value>) -> Option<u64> {
278    match value? {
279        Value::Number(number) => number.as_u64().or_else(|| {
280            number
281                .as_f64()
282                .filter(|v| v.fract() == 0.0 && *v >= 0.0 && *v <= 9_007_199_254_740_991.0)
283                .map(|v| v as u64)
284        }),
285        Value::String(text) => parse_counter(text.trim()),
286        _ => None,
287    }
288}
289
290/// Normalize counters read back from an execution record. Lenient, like the
291/// JavaScript reader: a malformed value never makes the record unreadable.
292pub fn normalize_cgroup_memory(value: &Value) -> Option<CgroupMemory> {
293    let object = value.as_object()?;
294    Some(CgroupMemory {
295        limit_bytes: counter_from_value(object.get("limitBytes")),
296        peak_bytes: counter_from_value(object.get("peakBytes")),
297        oom_events: counter_from_value(object.get("oomEvents")),
298        oom_kills: counter_from_value(object.get("oomKills")),
299    })
300}
301
302/// `deserialize_with` helper for `ExecutionRecord::cgroup_memory`.
303pub fn deserialize_cgroup_memory<'de, D>(deserializer: D) -> Result<Option<CgroupMemory>, D::Error>
304where
305    D: Deserializer<'de>,
306{
307    let value = Option::<Value>::deserialize(deserializer)?;
308    Ok(value.as_ref().and_then(normalize_cgroup_memory))
309}
310
311#[cfg(test)]
312mod tests {
313    use super::*;
314
315    #[test]
316    fn parses_counters_and_treats_max_as_no_limit() {
317        assert_eq!(
318            parse_cgroup_memory_sample("max 1024 0 2"),
319            Some(CgroupMemory {
320                limit_bytes: None,
321                peak_bytes: Some(1024),
322                oom_events: Some(0),
323                oom_kills: Some(2),
324            })
325        );
326        assert_eq!(parse_cgroup_memory_sample("max - - -"), None);
327        assert_eq!(parse_cgroup_memory_sample("1 2 3"), None);
328    }
329
330    #[test]
331    fn normalizes_floats_strings_and_nulls() {
332        let value = serde_json::json!({
333            "limitBytes": 268435456.0,
334            "peakBytes": "1024",
335            "oomEvents": null,
336            "oomKills": -1
337        });
338        assert_eq!(
339            normalize_cgroup_memory(&value),
340            Some(CgroupMemory {
341                limit_bytes: Some(268_435_456),
342                peak_bytes: Some(1024),
343                oom_events: None,
344                oom_kills: None,
345            })
346        );
347        assert_eq!(normalize_cgroup_memory(&Value::Null), None);
348    }
349}
start_command/cgroup_memory.rs

start_command/
cgroup_memory.rs
