Don't drop user's MaxDirectMemorySize flag on jdk8/windows (#48657)

* Always pass user-specified MaxDirectMemorySize

We had been testing whether a user had passed a value for
MaxDirectMemorySize by parsing the output of "java -XX:PrintFlagsFinal
-version". If MaxDirectMemorySize equals zero, we set it to half of max
heap. The problem is that on Windows with JDK 8, a JDK bug incorrectly
truncates values over 4g and returns multiples of 4g as zero. In order
to always respect the user-defined settings, we need to check our input
to see if an "-XX:MaxDirectMemorySize" value has been passed.

* Always warn for Windows/jdk8 ergo issue

Even if a user has set MaxDirectMemorySize, they aren't future-proof for
this JDK bug. With this change, we issue a general warning for the
windows/JDK8 issue, and a specific warning if MaxDirectMemorySize is
unset.

distribution/tools/launchers/src/main/java/org/elasticsearch/tools/launchers/JvmErgonomics.java

@@ -59,12 +59,20 @@ final class JvmErgonomics {
         final Map<String, Optional<String>> finalJvmOptions = finalJvmOptions(userDefinedJvmOptions);
         final long heapSize = extractHeapSize(finalJvmOptions);
         final long maxDirectMemorySize = extractMaxDirectMemorySize(finalJvmOptions);
-        if (maxDirectMemorySize == 0) {
+
+        if (System.getProperty("os.name").startsWith("Windows") && JavaVersion.majorVersion(JavaVersion.CURRENT) == 8) {
+            Launchers.errPrintln("Warning: with JDK 8 on Windows, Elasticsearch may be unable to derive correct");
+            Launchers.errPrintln("  ergonomic settings due to a JDK issue (JDK-8074459). Please use a newer");
+            Launchers.errPrintln("  version of Java.");
+        }
+
+        if (maxDirectMemorySize == 0 && userDefinedJvmOptions.stream().noneMatch(s -> s.startsWith("-XX:MaxDirectMemorySize"))) {
+
             if (System.getProperty("os.name").startsWith("Windows") && JavaVersion.majorVersion(JavaVersion.CURRENT) == 8) {
-                Launchers.errPrintln("Warning: with JDK 8 on Windows, Elasticsearch may miscalculate MaxDirectMemorySize");
+                Launchers.errPrintln("Warning: MaxDirectMemorySize may have been miscalculated due to JDK-8074459.");
-                Launchers.errPrintln("  due to a JDK issue (JDK-8074459).");
+                Launchers.errPrintln("  Please use a newer version of Java or set MaxDirectMemorySize explicitly.");
-                Launchers.errPrintln("  Please use a newer version of Java or set MaxDirectMemorySize explicitly");
             }
+
             ergonomicChoices.add("-XX:MaxDirectMemorySize=" + heapSize / 2);
         }
         return ergonomicChoices;

distribution/tools/launchers/src/test/java/org/elasticsearch/tools/launchers/JvmErgonomicsTests.java

@@ -25,6 +25,7 @@ import java.io.IOException;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 
 import static org.hamcrest.Matchers.anyOf;
@@ -142,8 +143,10 @@ public class JvmErgonomicsTests extends LaunchersTestCase {
     }
 
     public void testMaxDirectMemorySizeChoiceWhenSet() throws InterruptedException, IOException {
+        List<String> derivedSettingList = JvmErgonomics.choose(Arrays.asList("-Xms5g", "-Xmx5g", "-XX:MaxDirectMemorySize=4g"));
         assertThat(
-                JvmErgonomics.choose(Arrays.asList("-Xms1g", "-Xmx1g", "-XX:MaxDirectMemorySize=1g")),
+                derivedSettingList,
+                // if MaxDirectMemorySize is set, we shouldn't derive our own value for it
                 everyItem(not(startsWith("-XX:MaxDirectMemorySize="))));
     }