* (global): added --no-mem-optimization flag

This commit adds a new command-line argument that disables memory
optimizations AGH is using. These memory optimizations might be
necessary on low-memory devices, but they aren't free and there's a
performance hit (see #2044). Now they can be disabled - just pass
--no-mem-optimization when you run AGH or when you install the service
-- ./AdGuardHome -s install --no-mem-optimization

Closes: #2044

home/home.go

@@ -161,6 +161,9 @@ func run(args options) {
 	// configure log level and output
 	configureLogger(args)
 
+	// Go memory hacks
+	memoryUsage(args)
+
 	// print the first message after logger is configured
 	log.Println(version())
 	log.Debug("Current working directory is %s", Context.workDir)

home/memory.go

@@ -0,0 +1,44 @@
+package home
+
+import (
+	"os"
+	"runtime/debug"
+	"time"
+
+	"github.com/AdguardTeam/golibs/log"
+)
+
+// memoryUsage implements a couple of not really beautiful hacks which purpose is to
+// make OS reclaim the memory freed by AdGuard Home as soon as possible.
+// See this for the details on the performance hits & gains:
+// https://github.com/AdguardTeam/AdGuardHome/issues/2044#issuecomment-687042211
+func memoryUsage(args options) {
+	if args.disableMemoryOptimization {
+		log.Info("Memory optimization is disabled")
+		return
+	}
+
+	// Makes Go allocate heap at a slower pace
+	// By default we keep it at 50%
+	debug.SetGCPercent(50)
+
+	// madvdontneed: setting madvdontneed=1 will use MADV_DONTNEED
+	// instead of MADV_FREE on Linux when returning memory to the
+	// kernel. This is less efficient, but causes RSS numbers to drop
+	// more quickly.
+	_ = os.Setenv("GODEBUG", "madvdontneed=1")
+
+	// periodically call "debug.FreeOSMemory" so
+	// that the OS could reclaim the free memory
+	go func() {
+		ticker := time.NewTicker(5 * time.Minute)
+		for {
+			select {
+			case t := <-ticker.C:
+				t.Second()
+				log.Debug("Free OS memory")
+				debug.FreeOSMemory()
+			}
+		}
+	}()
+}

home/options.go

@@ -24,7 +24,11 @@ type options struct {
 	// runningAsService flag is set to true when options are passed from the service runner
 	runningAsService bool
 
-	glinetMode bool // Activate GL-Inet mode
+	// disableMemoryOptimization - disables memory optimization hacks
+	// see memoryUsage() function for the details
+	disableMemoryOptimization bool
+
+	glinetMode bool // Activate GL-Inet compatibility mode
 }
 
 // functions used for their side-effects
@@ -151,6 +155,13 @@ var noCheckUpdateArg = arg{
 	func(o options) []string { return boolSliceOrNil(o.disableUpdate) },
 }
 
+var disableMemoryOptimizationArg = arg{
+	"Disable memory optimization",
+	"no-mem-optimization", "",
+	nil, func(o options) (options, error) { o.disableMemoryOptimization = true; return o, nil }, nil,
+	func(o options) []string { return boolSliceOrNil(o.disableMemoryOptimization) },
+}
+
 var verboseArg = arg{
 	"Enable verbose output",
 	"verbose", "v",
@@ -194,6 +205,7 @@ func init() {
 		pidfileArg,
 		checkConfigArg,
 		noCheckUpdateArg,
+		disableMemoryOptimizationArg,
 		verboseArg,
 		glinetArg,
 		versionArg,

main.go

@@ -4,10 +4,6 @@
 package main
 
 import (
-	"os"
-	"runtime/debug"
-	"time"
-
 	"github.com/AdguardTeam/AdGuardHome/home"
 )
 
@@ -21,32 +17,5 @@ var channel = "release"
 var goarm = ""
 
 func main() {
-	memoryUsage()
-
 	home.Main(version, channel, goarm)
 }
-
-// memoryUsage implements a couple of not really beautiful hacks which purpose is to
-// make OS reclaim the memory freed by AdGuard Home as soon as possible.
-func memoryUsage() {
-	debug.SetGCPercent(10)
-
-	// madvdontneed: setting madvdontneed=1 will use MADV_DONTNEED
-	// instead of MADV_FREE on Linux when returning memory to the
-	// kernel. This is less efficient, but causes RSS numbers to drop
-	// more quickly.
-	_ = os.Setenv("GODEBUG", "madvdontneed=1")
-
-	// periodically call "debug.FreeOSMemory" so
-	// that the OS could reclaim the free memory
-	go func() {
-		ticker := time.NewTicker(15 * time.Second)
-		for {
-			select {
-			case t := <-ticker.C:
-				t.Second()
-				debug.FreeOSMemory()
-			}
-		}
-	}()
-}