feat: add gomemlimits debug logs for the amount of reserved memory

CHANGELOG.md

@@ -36,6 +36,7 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 - [#8484](https://github.com/thanos-io/thanos/pull/8484) Query: add `/api/v1/status/tsdb` API endpoint.
 - [#8454](https://github.com/thanos-io/thanos/pull/8454) Compact: ensure we don't mark blocks for deletion again after just deleting them
 - [#8410](https://github.com/thanos-io/thanos/pull/8410) Compact: ignore blocks with deletion mark in partial deletes
+- [#8556](https://github.com/thanos-io/thanos/pull/8556) All Components: add debug logs when enabling GOMEMLIMIT and log the effective memory limit on startup 
 
 ### Changed
 

cmd/thanos/config.go

@@ -349,24 +349,28 @@ func (gml *goMemLimitConfig) registerFlag(cmd extkingpin.FlagClause) *goMemLimit
 	return gml
 }
 
-func configureGoAutoMemLimit(common goMemLimitConfig) error {
+func configureGoAutoMemLimit(common goMemLimitConfig) (int64, error) {
+	var err error
+	limits := int64(-1)
+
 	if common.memlimitRatio <= 0.0 || common.memlimitRatio > 1.0 {
-		return errors.New("--auto-gomemlimit.ratio must be greater than 0 and less than or equal to 1.")
+		return limits, errors.New("--auto-gomemlimit.ratio must be greater than 0 and less than or equal to 1.")
 	}
 
 	if common.enableAutoGoMemlimit {
-		if _, err := memlimit.SetGoMemLimitWithOpts(
+		limits, err = memlimit.SetGoMemLimitWithOpts(
 			memlimit.WithRatio(common.memlimitRatio),
 			memlimit.WithProvider(
 				memlimit.ApplyFallback(
 					memlimit.FromCgroup,
 					memlimit.FromSystem,
 				),
 			),
-		); err != nil {
-			return errors.Wrap(err, "Failed to set GOMEMLIMIT automatically")
+		)
+		if err != nil {
+			return -1, errors.Wrap(err, "Failed to set GOMEMLIMIT automatically")
 		}
 	}
 
-	return nil
+	return limits, nil
 }

cmd/thanos/main.go

@@ -66,7 +66,8 @@ func main() {
 	cmd, setup := app.Parse()
 	logger := logging.NewLogger(*logLevel, *logFormat, *debugName)
 
-	if err := configureGoAutoMemLimit(goMemLimitConf); err != nil {
+	limits, err := configureGoAutoMemLimit(goMemLimitConf)
+	if err != nil {
 		level.Error(logger).Log("msg", "failed to configure Go runtime memory limits", "err", err)
 		os.Exit(1)
 	}
@@ -77,6 +78,11 @@ func main() {
 		level.Debug(logger).Log("msg", fmt.Sprintf(template, args...))
 	}))
 	defer undo()
+
+	if goMemLimitConf.enableAutoGoMemlimit {
+		level.Debug(logger).Log("msg", fmt.Sprintf("GOMEMLIMIT set to %d bytes configured with ratio equals to %.0f%% of detected memory", limits, goMemLimitConf.memlimitRatio*100))
+	}
+
 	if err != nil {
 		level.Warn(logger).Log("warn", errors.Wrapf(err, "failed to set GOMAXPROCS: %v", err))
 	}