PretenureSizeThreshol 设置对象超过多大时内存直接分配到老年代
1.7jdk默认垃圾收集器为 Parallel Scavenge(新生代)+Parallel Old(老年代) ,PretenureSizeThreshol在jdk1.7未指定垃圾收集器时未生效
private static final int _1MB = 1024 * 1024;
/**
* VM参数:-verbose:gc -Xms20M -Xmx20M -Xmn10M -XX:+PrintGCDetails -XX:SurvivorRatio=8 -XX:+PrintCommandLineFlags -XX:PretenureSizeThreshold=3145728-verbose:gc -Xms20M -Xmx20M -Xmn10M -XX:+PrintGCDetails -XX:SurvivorRatio=8 -XX:+PrintCommandLineFlags -XX:PretenureSizeThreshold=3145728 -XX:+UseSerialGC
*/ public static void testAllocation() { byte[] allocation1 = new byte[4 * _1MB]; }
gc日志显示数组并没有直接分配到老年代
-XX:InitialHeapSize=20971520 -XX:MaxHeapSize=20971520 -XX:MaxNewSize=10485760 -XX:NewSize=10485760 -XX:PretenureSizeThreshold=3145728 -XX:+PrintCommandLineFlags -XX:+PrintGC -XX:+PrintGCDetails -XX:SurvivorRatio=8 -XX:+UseCompressedOops -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC
Heap
PSYoungGen total 9216K, used 5097K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)
eden space 8192K, 62% used [0x00000000ff600000,0x00000000ffafa458,0x00000000ffe00000)
from space 1024K, 0% used [0x00000000fff00000,0x00000000fff00000,0x0000000100000000)
to space 1024K, 0% used [0x00000000ffe00000,0x00000000ffe00000,0x00000000fff00000)
ParOldGen total 10240K, used 0K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)
object space 10240K, 0% used [0x00000000fec00000,0x00000000fec00000,0x00000000ff600000)
PSPermGen total 21248K, used 2691K [0x00000000f9a00000, 0x00000000faec0000, 0x00000000fec00000)
object space 21248K, 12% used [0x00000000f9a00000,0x00000000f9ca0c80,0x00000000faec0000)
指定Serial收集器
-verbose:gc-Xms20M -Xmx20M -Xmn10M -XX:+PrintGCDetails -XX:SurvivorRatio=8-XX:+PrintCommandLineFlags -XX:PretenureSizeThreshold=3145728 -XX:+UseSerialGC
gc日志显示对象直接分配到老年代
-XX:InitialHeapSize=20971520 -XX:MaxHeapSize=20971520 -XX:MaxNewSize=10485760 -XX:NewSize=10485760 -XX:PretenureSizeThreshold=3145728 -XX:+PrintCommandLineFlags -XX:+PrintGC -XX:+PrintGCDetails -XX:SurvivorRatio=8 -XX:+UseCompressedOops -XX:-UseLargePagesIndividualAllocation -XX:+UseSerialGC
Heap
def new generation total 9216K, used 1001K [0x00000000f9a00000, 0x00000000fa400000, 0x00000000fa400000)
eden space 8192K, 12% used [0x00000000f9a00000, 0x00000000f9afa448, 0x00000000fa200000)
from space 1024K, 0% used [0x00000000fa200000, 0x00000000fa200000, 0x00000000fa300000)
to space 1024K, 0% used [0x00000000fa300000, 0x00000000fa300000, 0x00000000fa400000)
tenured generation total 10240K, used 4096K [0x00000000fa400000, 0x00000000fae00000, 0x00000000fae00000)
the space 10240K, 40% used [0x00000000fa400000, 0x00000000fa800010, 0x00000000fa800200, 0x00000000fae00000)
compacting perm gen total 21248K, used 2691K [0x00000000fae00000, 0x00000000fc2c0000, 0x0000000100000000)
the space 21248K, 12% used [0x00000000fae00000, 0x00000000fb0a0c80, 0x00000000fb0a0e00, 0x00000000fc2c0000)
No shared spaces configured.