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An Serviceability-Agent based tool to see stats of NIO direct memory for JDK8
import java.lang.reflect.*;
import java.lang.reflect.Method;
import java.util.*;
import sun.jvm.hotspot.memory.*;
import sun.jvm.hotspot.oops.*;
import sun.jvm.hotspot.debugger.*;
import sun.jvm.hotspot.runtime.*;
import sun.jvm.hotspot.tools.*;
import sun.jvm.hotspot.utilities.*;
public class DirectMemorySize extends Tool {
private boolean exactMallocMode;
private boolean verbose;
public DirectMemorySize(boolean exactMallocMode, boolean verbose) {
this.exactMallocMode = exactMallocMode;
this.verbose = verbose;
}
public void run() {
// Ready to go with the database...
try {
long reservedMemory = getStaticLongFieldValue("java.nio.Bits", "reservedMemory");
long directMemory = getStaticLongFieldValue("sun.misc.VM", "directMemory");
System.out.println("NIO direct memory: (in bytes)");
System.out.printf(" reserved size = %f MB (%d bytes)\n", toM(reservedMemory), reservedMemory);
System.out.printf(" max size = %f MB (%d bytes)\n", toM(directMemory), directMemory);
if (verbose) {
System.out.println("Currently allocated direct buffers:");
}
if (exactMallocMode || verbose) {
final long pageSize = getStaticIntFieldValue("java.nio.Bits", "pageSize");
ObjectHeap heap = VM.getVM().getObjectHeap();
InstanceKlass deallocatorKlass =
SystemDictionaryHelper.findInstanceKlass("java.nio.DirectByteBuffer$Deallocator");
final LongField addressField = (LongField) deallocatorKlass.findField("address", "J");
final IntField capacityField = (IntField) deallocatorKlass.findField("capacity", "I");
final int[] countHolder = new int[1];
heap.iterateObjectsOfKlass(new DefaultHeapVisitor() {
public boolean doObj(Oop oop) {
long address = addressField.getValue(oop);
if (address == 0) return false; // this deallocator has already been run
long capacity = capacityField.getValue(oop);
long mallocSize = capacity + pageSize;
countHolder[0]++;
if (verbose) {
System.out.printf(" 0x%016x: capacity = %f MB (%d bytes),"
+ " mallocSize = %f MB (%d bytes)\n",
address, toM(capacity), capacity,
toM(mallocSize), mallocSize);
}
return false;
}
}, deallocatorKlass, false);
if (exactMallocMode) {
long totalMallocSize = reservedMemory + pageSize * countHolder[0];
System.out.printf("NIO direct memory malloc'd size: %f MB (%d bytes)\n",
toM(totalMallocSize), totalMallocSize);
}
}
} catch (AddressException e) {
System.err.println("Error accessing address 0x"
+ Long.toHexString(e.getAddress()));
e.printStackTrace();
}
}
public static long getStaticLongFieldValue(String className, String fieldName) {
InstanceKlass klass = SystemDictionaryHelper.findInstanceKlass(className);
LongField field = (LongField) klass.findField(fieldName, "J");
return field.getValue(klass); // on JDK7 use: field.getValue(klass.getJavaMirror());
}
public static int getStaticIntFieldValue(String className, String fieldName) {
InstanceKlass klass = SystemDictionaryHelper.findInstanceKlass(className);
IntField field = (IntField) klass.findField(fieldName, "I");
return field.getValue(klass); // on JDK7 use: field.getValue(klass.getJavaMirror());
}
public static double toM(long value) {
return value / (1024 * 1024.0);
}
public String getName() {
return "directMemorySize";
}
protected void printFlagsUsage() {
System.out.println(" -e\tto print the actual size malloc'd");
System.out.println(" -v\tto print verbose info of every live DirectByteBuffer allocated from Java");
super.printFlagsUsage();
}
public static void main(String[] args) {
boolean exactMallocMode = false;
boolean verbose = false;
// argument processing logic copied from sun.jvm.hotspot.tools.JStack
int used = 0;
for (String arg : args) {
if ("-e".equals(arg)) {
exactMallocMode = true;
used++;
} else if ("-v".equals(arg)) {
verbose = true;
used++;
}
}
if (used != 0) {
args = Arrays.copyOfRange(args, used, args.length);
}
DirectMemorySize tool = new DirectMemorySize(exactMallocMode, verbose);
try {
Method start = Tool.class.getDeclaredMethod("start", Class.forName("[Ljava.lang.String;"));
start.setAccessible(true);
start.invoke(tool, new Object[]{args});
} catch (Exception e) {
e.printStackTrace();
}
tool.stop();
}
}
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