Enable auto-gomemlimit by default (#15372)

Enable the `auto-gomemlimit` feature flag by default.
* Add command line flag `--no-auto-gomemlimit` to disable.

Signed-off-by: SuperQ <superq@gmail.com>

cmd/prometheus/main.go

@@ -195,13 +195,14 @@ type flagConfig struct {
 	enableAutoReload   bool
 	autoReloadInterval model.Duration
 
-	featureList   []string
-	memlimitRatio float64
+	memlimitEnable bool
+	memlimitRatio  float64
+
+	featureList []string
 	// These options are extracted from featureList
 	// for ease of use.
 	enablePerStepStats       bool
 	enableAutoGOMAXPROCS     bool
-	enableAutoGOMEMLIMIT     bool
 	enableConcurrentRuleEval bool
 
 	prometheusURL   string
@@ -242,9 +243,6 @@ func (c *flagConfig) setFeatureListOptions(logger *slog.Logger) error {
 					c.autoReloadInterval, _ = model.ParseDuration("1s")
 				}
 				logger.Info("Enabled automatic configuration file reloading. Checking for configuration changes every", "interval", c.autoReloadInterval)
-			case "auto-gomemlimit":
-				c.enableAutoGOMEMLIMIT = true
-				logger.Info("Automatically set GOMEMLIMIT to match Linux container or system memory limit")
 			case "concurrent-rule-eval":
 				c.enableConcurrentRuleEval = true
 				logger.Info("Experimental concurrent rule evaluation enabled.")
@@ -331,6 +329,8 @@ func main() {
 	a.Flag("web.listen-address", "Address to listen on for UI, API, and telemetry. Can be repeated.").
 		Default("0.0.0.0:9090").StringsVar(&cfg.web.ListenAddresses)
 
+	a.Flag("auto-gomemlimit", "Automatically set GOMEMLIMIT to match Linux container or system memory limit").
+		Default("true").BoolVar(&cfg.memlimitEnable)
 	a.Flag("auto-gomemlimit.ratio", "The ratio of reserved GOMEMLIMIT memory to the detected maximum container or system memory").
 		Default("0.9").FloatVar(&cfg.memlimitRatio)
 
@@ -514,7 +514,7 @@ func main() {
 	a.Flag("scrape.discovery-reload-interval", "Interval used by scrape manager to throttle target groups updates.").
 		Hidden().Default("5s").SetValue(&cfg.scrape.DiscoveryReloadInterval)
 
-	a.Flag("enable-feature", "Comma separated feature names to enable. Valid options: auto-gomemlimit, exemplar-storage, expand-external-labels, memory-snapshot-on-shutdown, promql-per-step-stats, promql-experimental-functions, extra-scrape-metrics, auto-gomaxprocs, native-histograms, created-timestamp-zero-ingestion, concurrent-rule-eval, delayed-compaction, old-ui. See https://prometheus.io/docs/prometheus/latest/feature_flags/ for more details.").
+	a.Flag("enable-feature", "Comma separated feature names to enable. Valid options: exemplar-storage, expand-external-labels, memory-snapshot-on-shutdown, promql-per-step-stats, promql-experimental-functions, extra-scrape-metrics, auto-gomaxprocs, native-histograms, created-timestamp-zero-ingestion, concurrent-rule-eval, delayed-compaction, old-ui. See https://prometheus.io/docs/prometheus/latest/feature_flags/ for more details.").
 		Default("").StringsVar(&cfg.featureList)
 
 	a.Flag("agent", "Run Prometheus in 'Agent mode'.").BoolVar(&agentMode)
@@ -765,7 +765,7 @@ func main() {
 		}
 	}
 
-	if cfg.enableAutoGOMEMLIMIT {
+	if cfg.memlimitEnable {
 		if _, err := memlimit.SetGoMemLimitWithOpts(
 			memlimit.WithRatio(cfg.memlimitRatio),
 			memlimit.WithProvider(

docs/command-line/prometheus.md

@@ -17,6 +17,7 @@ The Prometheus monitoring server
 | <code class="text-nowrap">--config.file</code> | Prometheus configuration file path. | `prometheus.yml` |
 | <code class="text-nowrap">--config.auto-reload-interval</code> | Specifies the interval for checking and automatically reloading the Prometheus configuration file upon detecting changes. | `30s` |
 | <code class="text-nowrap">--web.listen-address</code> <code class="text-nowrap">...<code class="text-nowrap"> | Address to listen on for UI, API, and telemetry. Can be repeated. | `0.0.0.0:9090` |
+| <code class="text-nowrap">--auto-gomemlimit</code> | Automatically set GOMEMLIMIT to match Linux container or system memory limit | `true` |
 | <code class="text-nowrap">--auto-gomemlimit.ratio</code> | The ratio of reserved GOMEMLIMIT memory to the detected maximum container or system memory | `0.9` |
 | <code class="text-nowrap">--web.config.file</code> | [EXPERIMENTAL] Path to configuration file that can enable TLS or authentication. |  |
 | <code class="text-nowrap">--web.read-timeout</code> | Maximum duration before timing out read of the request, and closing idle connections. | `5m` |
@@ -58,7 +59,7 @@ The Prometheus monitoring server
 | <code class="text-nowrap">--query.timeout</code> | Maximum time a query may take before being aborted. Use with server mode only. | `2m` |
 | <code class="text-nowrap">--query.max-concurrency</code> | Maximum number of queries executed concurrently. Use with server mode only. | `20` |
 | <code class="text-nowrap">--query.max-samples</code> | Maximum number of samples a single query can load into memory. Note that queries will fail if they try to load more samples than this into memory, so this also limits the number of samples a query can return. Use with server mode only. | `50000000` |
-| <code class="text-nowrap">--enable-feature</code> <code class="text-nowrap">...<code class="text-nowrap"> | Comma separated feature names to enable. Valid options: auto-gomemlimit, exemplar-storage, expand-external-labels, memory-snapshot-on-shutdown, promql-per-step-stats, promql-experimental-functions, extra-scrape-metrics, auto-gomaxprocs, native-histograms, created-timestamp-zero-ingestion, concurrent-rule-eval, delayed-compaction, old-ui. See https://prometheus.io/docs/prometheus/latest/feature_flags/ for more details. |  |
+| <code class="text-nowrap">--enable-feature</code> <code class="text-nowrap">...<code class="text-nowrap"> | Comma separated feature names to enable. Valid options: exemplar-storage, expand-external-labels, memory-snapshot-on-shutdown, promql-per-step-stats, promql-experimental-functions, extra-scrape-metrics, auto-gomaxprocs, native-histograms, created-timestamp-zero-ingestion, concurrent-rule-eval, delayed-compaction, old-ui. See https://prometheus.io/docs/prometheus/latest/feature_flags/ for more details. |  |
 | <code class="text-nowrap">--agent</code> | Run Prometheus in 'Agent mode'. |  |
 | <code class="text-nowrap">--log.level</code> | Only log messages with the given severity or above. One of: [debug, info, warn, error] | `info` |
 | <code class="text-nowrap">--log.format</code> | Output format of log messages. One of: [logfmt, json] | `logfmt` |

docs/feature_flags.md

@@ -53,14 +53,6 @@ computed at all.
 
 When enabled, GOMAXPROCS variable is automatically set to match Linux container CPU quota.
 
-## Auto GOMEMLIMIT
-
-`--enable-feature=auto-gomemlimit`
-
-When enabled, the GOMEMLIMIT variable is automatically set to match the Linux container memory limit. If there is no container limit, or the process is running outside of containers, the system memory total is used.
-
-There is also an additional tuning flag, `--auto-gomemlimit.ratio`, which allows controlling how much of the memory is used for Prometheus. The remainder is reserved for memory outside the process. For example, kernel page cache. Page cache is important for Prometheus TSDB query performance. The default is `0.9`, which means 90% of the memory limit will be used for Prometheus.
-
 ## Native Histograms
 
 `--enable-feature=native-histograms`