标签：system 对象 span 程序 elar page oop alt serial
在主函数中通过下如下方法实时打印没创建一个对象后查看内存情况：
private static void printRuntimeMemoryInfo(String str) { System.out.println("================= " + str + " ================"); Runtime runtime = Runtime.getRuntime(); System.out.println("max memory: " + runtime.maxMemory()); System.out.println("free memory: " + runtime.freeMemory()); System.out.println("tatal memory: " + runtime.totalMemory()); }
注：
当前进程设置的参数为-Xms5m -Xmx10m -XX:+PrintGCDetails -XX:+UseSerialGC -XX:+PrintCommandLineFlags
程序运行后的结果如下：
1 -XX:InitialHeapSize=5242880 -XX:MaxHeapSize=10485760 -XX:+PrintCommandLineFlags -XX:+PrintGCDetails -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:-UseLargePagesIndividualAllocation -XX:+UseSerialGC 2 ======================= 初始状态 ============================== 3 max memory: 10158080 4 free memory: 5175632 5 tatal memory: 6094848 6 ======================= b1 ============================== 7 max memory: 10158080 8 free memory: 4651328 9 tatal memory: 6094848 10 [GC (Allocation Failure) [DefNew: 1409K->191K(1856K), 0.0011437 secs] 1409K->1070K(5952K), 0.0011870 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] 11 ======================= b2 ============================== 12 max memory: 10158080 13 free memory: 4441040 14 tatal memory: 6094848 15 ======================= b3 ============================== 16 max memory: 10158080 17 free memory: 3916736 18 tatal memory: 6094848 19 ======================= b4 ============================== 20 max memory: 10158080 21 free memory: 3392432 22 tatal memory: 6094848 23 [GC (Allocation Failure) [DefNew: 1760K->0K(1856K), 0.0010500 secs] 2639K->2606K(5952K), 0.0010660 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] 24 ======================= b5 ============================== 25 max memory: 10158080 26 free memory: 2867912 27 tatal memory: 6094848 28 ======================= b6 ============================== 29 max memory: 10158080 30 free memory: 2343608 31 tatal memory: 6094848 32 ======================= b7 ============================== 33 max memory: 10158080 34 free memory: 1819304 35 tatal memory: 6094848 36 [GC (Allocation Failure) [DefNew: 1568K->0K(1856K), 0.0015055 secs][Tenured: 4142K->4142K(4612K), 0.0013368 secs] 4175K->4142K(6468K), [Metaspace: 2714K->2714K(1056768K)], 0.0028898 secs] [Times: user=0.02 sys=0.00, real=0.00 secs] 37 ======================= b8 ============================== 38 max memory: 10158080 39 free memory: 5336216 40 tatal memory: 10158080 41 ======================= b9 ============================== 42 max memory: 10158080 43 free memory: 4811912 44 tatal memory: 10158080 45 ======================= b10 ============================== 46 max memory: 10158080 47 free memory: 4287608 48 tatal memory: 10158080 49 ======================= b11 ============================== 50 max memory: 10158080 51 free memory: 3763304 52 tatal memory: 10158080 53 ======================= b12 ============================== 54 max memory: 10158080 55 free memory: 3239000 56 tatal memory: 10158080 57 [GC (Allocation Failure) [DefNew: 2614K->0K(3072K), 0.0011039 secs] 6756K->6703K(9920K), 0.0011251 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] 58 ======================= b13 ============================== 59 max memory: 10158080 60 free memory: 2714440 61 tatal memory: 10158080 62 ======================= b14 ============================== 63 max memory: 10158080 64 free memory: 2190136 65 tatal memory: 10158080 66 ======================= b15 ============================== 67 max memory: 10158080 68 free memory: 1665832 69 tatal memory: 10158080 70 ======================= b16 ============================== 71 max memory: 10158080 72 free memory: 1113336 73 tatal memory: 10158080 74 ======================= b17 ============================== 75 max memory: 10158080 76 free memory: 589032 77 tatal memory: 10158080 78 [GC (Allocation Failure) [DefNew: 2641K->2641K(3072K), 0.0000071 secs][Tenured: 6702K->6702K(6848K), 0.0015729 secs] 9344K->9263K(9920K), [Metaspace: 2716K->2716K(1056768K)], 0.0016249 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] 79 [Full GC (Allocation Failure) [Tenured: 6702K->6688K(6848K), 0.0019453 secs] 9263K->9249K(9920K), [Metaspace: 2716K->2716K(1056768K)], 0.0019585 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] 80 Exception in thread "main" java.lang.OutOfMemoryError: Java heap space 81 at com.shif.test.JvmMemaryTest.main(JvmMemaryTest.java:80) 82 Heap 83 def new generation total 3072K, used 2669K [0x00000000ff600000, 0x00000000ff950000, 0x00000000ff950000) 84 eden space 2752K, 97% used [0x00000000ff600000, 0x00000000ff89b760, 0x00000000ff8b0000) 85 from space 320K, 0% used [0x00000000ff900000, 0x00000000ff900000, 0x00000000ff950000) 86 to space 320K, 0% used [0x00000000ff8b0000, 0x00000000ff8b0000, 0x00000000ff900000) 87 tenured generation total 6848K, used 6688K [0x00000000ff950000, 0x0000000100000000, 0x0000000100000000) 88 the space 6848K, 97% used [0x00000000ff950000, 0x00000000fffd81e0, 0x00000000fffd8200, 0x0000000100000000) 89 Metaspace used 2746K, capacity 4486K, committed 4864K, reserved 1056768K 90 class space used 305K, capacity 386K, committed 512K, reserved 1048576K
通过运行结果可以得出以下结论：
1 当前进程能申请到的的最大内存为maxMemory()；
2 totalMemory()返回的是我们程序当前已经申请到的内存大小；
3 freeMemorm()返回的是已经申请到的内存还有多少没有用；
(以上数据会有一些误差)
标签：system 对象 span 程序 elar page oop alt serial
原文地址：https://www.cnblogs.com/fpsfzy/p/jvm.html
