Add the option to configure memory ballast for Loki

CHANGELOG.md

@@ -1,5 +1,5 @@
 ## Main
-
+* [5081](https://github.com/grafana/loki/pull/5081) **SasSwart**: Add the option to configure memory ballast for Loki
 * [5067](https://github.com/grafana/loki/pull/5057) **cstyan**: Add a metric to Azure Blob Storage client to track total egress bytes
 * [4950](https://github.com/grafana/loki/pull/4950) **DylanGuedes**: Implement common instance addr/net interface
 * [4949](https://github.com/grafana/loki/pull/4949) **ssncferreira**: Add query `queueTime` metric to statistics and metrics.go

cmd/loki/main.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"reflect"
+	"runtime"
 
 	"github.com/go-kit/log/level"
 	"github.com/prometheus/common/version"
@@ -87,6 +88,9 @@ func main() {
 		}()
 	}
 
+	ballast := make([]byte, config.BallastBytes)
+	runtime.KeepAlive(ballast)
+
 	// Start Loki
 	t, err := loki.New(config.Config)
 	util_log.CheckFatal("initialising loki", err)

pkg/loki/config_wrapper.go

@@ -35,6 +35,7 @@ type ConfigWrapper struct {
 	LogConfig       bool
 	ConfigFile      string
 	ConfigExpandEnv bool
+	BallastBytes    int
 }
 
 func (c *ConfigWrapper) RegisterFlags(f *flag.FlagSet) {
@@ -46,6 +47,8 @@ func (c *ConfigWrapper) RegisterFlags(f *flag.FlagSet) {
 		"level with the order reversed, reversing the order makes viewing the entries easier in Grafana.")
 	f.StringVar(&c.ConfigFile, "config.file", "", "yaml file to load")
 	f.BoolVar(&c.ConfigExpandEnv, "config.expand-env", false, "Expands ${var} in config according to the values of the environment variables.")
+	f.IntVar(&c.BallastBytes, "config.ballast-bytes", 0, "The amount of virtual memory to reserve as a ballast in order to optimise "+
+		"garbage collection.")
 	c.Config.RegisterFlags(f)
 }