Java8元空间和堆使用

Question

我有这个代码动态生成类并加载它

import javassist.CannotCompileException;
import javassist.ClassPool;

public class PermGenLeak {
    private static final String PACKAGE_NAME = "com.jigarjoshi.permgenleak.";

    public static void main(String[] args) throws CannotCompileException, InterruptedException {
        for (int i = 0; i < Integer.MAX_VALUE; i++) {
            ClassPool pool = ClassPool.getDefault();
            pool.makeClass(PACKAGE_NAME + i).toClass();
            Thread.sleep(3);
        }

    }
}

我针对Java 7(jdk1.7.0_60)启动了这个类,正如预期的那样,它填满了PermGenSpace并且堆仍未使用 _{图像显示permgen使用超时,最后JVM终止}

现在相同的代码针对Java 8(jdk1.8.0_40-ea)运行并且正如预期的那样它继续扩展本机内存(Metaspace)但令人惊讶的是,1g的Metaspace它在OldGen中消耗了3g的堆(随着时间的推移,几乎是Metaspace的3倍)

_{该图显示了Metaspace使用超时和系统内存使用示例}

这封来自Jon Masamitsu的电子邮件和这张JEP门票说

interned String和Class stats以及一些misc数据已移至Heap

当它将更多类加载到Metaspace中时,究竟是什么导致了堆的增加？

Answer 1

运行jmap -histo PID以查看哪些对象占用堆空间.
当我运行你的例子时,我看到堆满了Javassist辅助对象:

 num     #instances         #bytes  class name
----------------------------------------------
   1:        592309      312739152  [Ljavassist.bytecode.ConstInfo;
   2:       6515673      208501536  java.util.HashMap$Node
   3:       2964403      169188824  [C
   4:       1777622      102165184  [Ljava.lang.Object;
   5:       4146200       99508800  javassist.bytecode.Utf8Info
   6:       3553889       85293336  java.util.ArrayList
   7:       2964371       71144904  java.lang.String
   8:        593075       56944008  java.lang.Class
   9:        592332       47388032  [Ljava.util.HashMap$Node;
  10:        592309       37907776  javassist.bytecode.ClassFile
  11:        592308       37907712  javassist.CtNewClass
  12:       1185118       28555808  [B
  13:        592342       28432416  java.util.HashMap
  14:       1184624       28430976  javassist.bytecode.ClassInfo
  15:        592309       28430832  [[Ljavassist.bytecode.ConstInfo;
  16:        592322       23692880  javassist.bytecode.MethodInfo
  17:        592315       23692600  javassist.bytecode.CodeAttribute
  18:        592434       18957888  java.util.Hashtable$Entry
  19:        592309       18953888  javassist.bytecode.ConstPool
  20:        592308       18953856  java.lang.ref.WeakReference
  21:        592318       14215632  javassist.bytecode.MethodrefInfo
  22:        592318       14215632  javassist.bytecode.NameAndTypeInfo
  23:        592315       14215560  javassist.bytecode.ExceptionTable
  24:        592309       14215416  javassist.bytecode.LongVector
  25:        592309       14215416  javassist.bytecode.SourceFileAttribute
  26:        592507        9487584  [I
  27:             8        6292528  [Ljava.util.Hashtable$Entry;
  28:           212          18656  java.lang.reflect.Method
  29:           407          13024  java.util.concurrent.ConcurrentHashMap$Node
  30:           124           8928  java.lang.reflect.Field