IBM JVM 1.4.2 32位在AIX 64位操作系统下最大能使用偶然2814m内存，多次测试能使用2940271104字节(2802MB)

小灰灰 2023-10-05 16:10 68阅读 0赞

如下是Java 内存消耗程序的源代码。其目的是消耗所有JVM内存（RAM）。它尝试分配1 MB的字节数组，直到用完JVM RAM。

import java.util.Vector;
    
    public class MemoryEater {
        public static void main(String[] args) {
            Vector v = new Vector();
            int i = 0;
            while (true) {
                byte b[] = new byte[1048576];
                v.add(b);
                i = i + 1;
                Runtime rt = Runtime.getRuntime();
                System.out.println("Total Memory = " +
                    rt.totalMemory() +
                    " Free Memory = " +
                    rt.freeMemory() +
                    " Allocated Memory = " +
                    i +
                    "MB");
            }
        }
    }

使用选项（如下所示）运行此**Java** **内存**消耗程序也很重要，-Xmx以确保您的JVM获得了您希望它拥有的所有**内存**：

$ **java** **-Xmx1024M MemoryEater**

上面显示的示例将尝试消耗多达1,024 MB RAM（1 GB）。

IBM J9 JDK 1.4.2 32bit On AIX6.1 64 bit测试结果:

**\# /usr/java14/bin/java -Xmx6910m MemoryEater**  
Total Memory = 2950756864 Free Memory = 2948381040  
Total Memory = 2950756864 Free Memory = 2947332448

...

Total Memory = 2950756864 Free Memory = 1073272  
JVMDG217: Dump Handler is Processing OutOfMemory - Please Wait.  
JVMDG315: JVM Requesting Heap dump file  
JVMDG318: Heap dump file written to //heapdump18743486.1608351347.phd  
JVMDG303: JVM Requesting Java core file  
JVMDG304: Java core file written to //javacore18743486.1608351348.txt  
JVMDG274: Dump Handler has Processed OutOfMemory.  
JVMST109: Insufficient space in Javaheap to satisfy allocation request  
Exception in thread "main" java.lang.OutOfMemoryError  
at MemoryEater.main(MemoryEater.java(Compiled Code))

**2950756864/1024/1024=2814.061035MB**

**可见****-Xmx6910m并不代表真正可以使用6910m内存。实际最大可以使用2814m，最好实际配置时 -Xmx小于2814m。**

另一时间在上面统一台AIX上测试

Total Memory = 2940271104 Free Memory = 2122008  
Total Memory = 2940271104 Free Memory = 1073416  
JVMDG217: Dump Handler is Processing OutOfMemory - Please Wait.  
JVMDG315: JVM Requesting Heap dump file  
JVMDG318: Heap dump file written to //heapdump19595290.1608435853.phd  
JVMDG303: JVM Requesting Java core file  
JVMDG304: Java core file written to //javacore19595290.1608435854.txt  
JVMDG274: Dump Handler has Processed OutOfMemory.  
JVMST109: Insufficient space in Javaheap to satisfy allocation request  
Exception in thread "main" java.lang.OutOfMemoryError  
at MemoryEater.main(MemoryEater.java(Compiled Code))

\# /usr/java14/bin/java -version  
java version "1.4.2"  
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2)  
Classic VM (build 1.4.2, J2RE 1.4.2 IBM AIX build ca142ifx-20130618 (SR13 FP18) (JIT enabled: jitc))  
\# oslevel -s  
6100-09-04-1441  
\#

**另一台AIXJAVA最大可使用内存小很多**

**Total Memory = 1996618240 Free Memory = 1070744  
JVMDG217: Dump Handler is Processing OutOfMemory - Please Wait.  
JVMDG315: JVM Requesting Heap dump file  
JVMDG318: Heap dump file written to //heapdump119008.1608435566.phd  
JVMDG303: JVM Requesting Java core file  
JVMDG304: Java core file written to //javacore119008.1608435567.txt  
JVMDG274: Dump Handler has Processed OutOfMemory.  
JVMST109: Insufficient space in Javaheap to satisfy allocation request  
Exception in thread "main" java.lang.OutOfMemoryError  
at MemoryEater.main(MemoryEater.java(Compiled Code))  
\# /usr/java14/bin/java -version  
java version "1.4.2"  
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2)  
Classic VM (build 1.4.2, J2RE 1.4.2 IBM AIX build ca142ifx-20110418 (SR13 FP9) (JIT enabled: jitc))  
\# oslevel -s  
5300-12-08-1316  
\#**

将jdk 升级补丁后,**JAVA最大可使用内存增大了，应该是SR13 FP9的 一个BUG。**

Total Memory = 2940271104 Free Memory = 2123176  
Total Memory = 2940271104 Free Memory = 1074584  
JVMDG217: Dump Handler is Processing OutOfMemory - Please Wait.  
JVMDG315: JVM Requesting Heap dump file  
JVMDG318: Heap dump file written to //heapdump536720.1608437021.phd  
JVMDG303: JVM Requesting Java core file  
JVMDG304: Java core file written to //javacore536720.1608437022.txt  
JVMDG274: Dump Handler has Processed OutOfMemory.  
JVMST109: Insufficient space in Javaheap to satisfy allocation request  
Exception in thread "main" java.lang.OutOfMemoryError  
at MemoryEater.main(MemoryEater.java(Compiled Code))  
\#

**又一台**

**Total Memory = 2940271104 Free Memory = 2101680  
Total Memory = 2940271104 Free Memory = 1090344  
JVMDG217: Dump Handler is Processing OutOfMemory - Please Wait.  
JVMDG315: JVM Requesting Heap dump file  
JVMDG318: Heap dump file written to //heapdump26232102.1608436120.phd  
JVMDG303: JVM Requesting Java core file  
JVMDG304: Java core file written to //javacore26232102.1608436120.txt  
JVMDG274: Dump Handler has Processed OutOfMemory.  
JVMST109: Insufficient space in Javaheap to satisfy allocation request  
Exception in thread "main" java.lang.OutOfMemoryError  
at MemoryEater.main(MemoryEater.java(Compiled Code))  
\# oslevel -s  
5300-06-06-0811  
\#**

**\# /usr/java14/bin/java -version  
java version "1.4.2"  
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2)  
Classic VM (build 1.4.2, J2RE 1.4.2 IBM AIX build ca142-20061124 (SR7) (JIT enab led: jitc))**

**又进行测试**

**Total Memory = 2940271104 Free Memory = 2122768 Allocated Memory = 2801MB  
Total Memory = 2940271104 Free Memory = 1074176 Allocated Memory = 2802MB  
JVMDG217: Dump Handler is Processing OutOfMemory - Please Wait.  
JVMDG315: JVM Requesting Heap dump file  
JVMDG318: Heap dump file written to //heapdump344230.1608548867.phd  
JVMDG303: JVM Requesting Java core file  
JVMDG304: Java core file written to //javacore344230.1608548868.txt  
JVMDG274: Dump Handler has Processed OutOfMemory.  
JVMST109: Insufficient space in Javaheap to satisfy allocation request  
Exception in thread "main" java.lang.OutOfMemoryError  
at MemoryEater.main(MemoryEater.java(Compiled Code))  
\#**