feat: add java optimisation flags

.cargo/config.toml

@@ -1,2 +1,2 @@
 [alias]
-runs = "run -- paper --config data/config --backup data/backups --world data/worlds --jar data/paper.jar"
+runs = "run -- paper 1.19.4-545 --config data/config --backup data/backups --world data/worlds --jar data/paper.jar"

src/server/command.rs

@@ -113,16 +113,57 @@ impl ServerCommand {
         let backup_dir = self.backup_dir.canonicalize()?;
 
         self.accept_eula()?;
+        let mut cmd = Command::new(&self.java);
 
-        let child = Command::new(&self.java)
-            .current_dir(&config_dir)
+        // Apply JVM optimisation flags
+        // https://aikar.co/2018/07/02/tuning-the-jvm-g1gc-garbage-collector-flags-for-minecraft/
+        cmd.arg(format!("-Xms{}M", self.xms))
+            .arg(format!("-Xmx{}M", self.xmx))
+            .args([
+                "-XX:+UseG1GC",
+                "-XX:+ParallelRefProcEnabled",
+                "-XX:MaxGCPauseMillis=200",
+                "-XX:+UnlockExperimentalVMOptions",
+                "-XX:+DisableExplicitGC",
+                "-XX:+AlwaysPreTouch",
+                "-XX:G1HeapWastePercent=5",
+                "-XX:G1MixedGCCountTarget=4",
+                "-XX:G1MixedGCLiveThresholdPercent=90",
+                "-XX:G1RSetUpdatingPauseTimePercent=5",
+                "-XX:SurvivorRatio=32",
+                "-XX:+PerfDisableSharedMem",
+                "-XX:MaxTenuringThreshold=1",
+                "-Dusing.aikars.flags=https://mcflags.emc.gs",
+                "-Daikars.new.flags=true",
+            ]);
+
+        if self.xms > 12 * 1024 {
+            cmd.args([
+                "-XX:G1NewSizePercent=40",
+                "-XX:G1MaxNewSizePercent=50",
+                "-XX:G1HeapRegionSize=16M",
+                "-XX:G1ReservePercent=15",
+                "-XX:InitiatingHeapOccupancyPercent=20",
+            ]);
+        } else {
+            cmd.args([
+                "-XX:G1NewSizePercent=30",
+                "-XX:G1MaxNewSizePercent=40",
+                "-XX:G1HeapRegionSize=8M",
+                "-XX:G1ReservePercent=15",
+                "-XX:InitiatingHeapOccupancyPercent=15",
+            ]);
+        }
+
+        cmd.current_dir(&config_dir)
             .arg("-jar")
             .arg(&jar)
             .arg("--universe")
             .arg(&world_dir)
             .arg("--nogui")
-            .stdin(Stdio::piped())
-            .spawn()?;
+            .stdin(Stdio::piped());
+
+        let child = cmd.spawn()?;
 
         Ok(ServerProcess::new(
             self.type_,