Java メモリの割り当てとリサイクル戦略の分析

public class ReflectTest {

  private static final int _1MB = 1024*1024;
  
  public static void testAllocation(){
    byte[] allocation1 , allocation2 , allocation3 , allocation4;
    allocation1 = new byte[2 * _1MB];
    allocation2 = new byte[2 * _1MB];
    allocation3 = new byte[2 * _1MB];
    allocation4 = new byte[6 * _1MB];
  }
  
  public static void main(String[] args) {
    ReflectTest.testAllocation();
  }
  
}

Heap
 PSYoungGen   total 9216K, used 6651K [0x000000000b520000, 0x000000000bf20000, 0x000000000bf20000)
 eden space 8192K, 81% used [0x000000000b520000,0x000000000bb9ef28,0x000000000bd20000)
 from space 1024K, 0% used [0x000000000be20000,0x000000000be20000,0x000000000bf20000)
 to  space 1024K, 0% used [0x000000000bd20000,0x000000000bd20000,0x000000000be20000)
 PSOldGen    total 10240K, used 6144K [0x000000000ab20000, 0x000000000b520000, 0x000000000b520000)
 object space 10240K, 60% used [0x000000000ab20000,0x000000000b120018,0x000000000b520000)
 PSPermGen    total 21248K, used 2973K [0x0000000005720000, 0x0000000006be0000, 0x000000000ab20000)
 object space 21248K, 13% used [0x0000000005720000,0x0000000005a07498,0x0000000006be0000)

public class ReflectTestBig {

  private static final int _1MB = 1024*1024;
  
  public static void testAllocation(){
    byte[] allocation2 , allocation3 , allocation4;
    allocation2 = new byte[2 * _1MB];
    allocation3 = new byte[2 * _1MB];
    allocation4 = new byte[6 * _1MB];
  }
  
  public static void main(String[] args) {
    ReflectTestBig.testAllocation();
  }
  
}

Heap
 PSYoungGen   total 8960K, used 4597K [0x000000000b510000, 0x000000000bf10000, 0x000000000bf10000)
 eden space 7680K, 59% used [0x000000000b510000,0x000000000b98d458,0x000000000bc90000)
 from space 1280K, 0% used [0x000000000bdd0000,0x000000000bdd0000,0x000000000bf10000)
 to  space 1280K, 0% used [0x000000000bc90000,0x000000000bc90000,0x000000000bdd0000)
 PSOldGen    total 10240K, used 6144K [0x000000000ab10000, 0x000000000b510000, 0x000000000b510000)
 object space 10240K, 60% used [0x000000000ab10000,0x000000000b110018,0x000000000b510000)
 PSPermGen    total 21248K, used 2973K [0x0000000005710000, 0x0000000006bd0000, 0x000000000ab10000)
 object space 21248K, 13% used [0x0000000005710000,0x00000000059f7460,0x0000000006bd0000)

public class JavaTest { 
 
  static int m = 1024 * 1024; 
 
  public static void main(String[] args) { 
    byte[] a1 = new byte[1 * m / 4]; 

　　　　 byte[] a2 = new byte[7 * m]; 

　　　　 byte[] a3 = new byte[3 * m]; //GC 
  } 
}

[GC [DefNew: 7767K->403K(9216K), 0.0062209 secs] 7767K->7571K(19456K), 0.0062482 secs]  
[Times: user=0.00 sys=0.00, real=0.01 secs]  
a3 ok 
Heap 
 def new generation  total 9216K, used 3639K [0x331d0000, 0x33bd0000, 0x33bd0000) 
 eden space 8192K, 39% used [0x331d0000, 0x334f9040, 0x339d0000) 
 from space 1024K, 39% used [0x33ad0000, 0x33b34de8, 0x33bd0000) 
 to  space 1024K,  0% used [0x339d0000, 0x339d0000, 0x33ad0000) 
 tenured generation  total 10240K, used 7168K [0x33bd0000, 0x345d0000, 0x345d0000) 
  the space 10240K, 70% used [0x33bd0000, 0x342d0010, 0x342d0200, 0x345d0000) 
 compacting perm gen total 12288K, used 381K [0x345d0000, 0x351d0000, 0x385d0000) 
  the space 12288K,  3% used [0x345d0000, 0x3462f548, 0x3462f600, 0x351d0000) 
  ro space 10240K, 55% used [0x385d0000, 0x38b51140, 0x38b51200, 0x38fd0000) 
  rw space 12288K, 55% used [0x38fd0000, 0x396744c8, 0x39674600, 0x39bd0000)