why oom? and first gc why Tenured: 8192K->8961K(10240K)? tks : public class TestJVmRiZHI{

   
    /**
     jdk 1.8
     -XX:+UseSerialGC
     -verbose:gc
     -Xms20M
     -Xmx20m
     -Xmn10M
     -XX:+PrintGCDetails
     -XX:SurvivorRatio=8
     * @param args
     */     

    private  static final int _1mb = 1024 * 1024;

    public static void main(String[] args) {

        Byte[] allocation1 = new Byte[2*_1mb];

        Byte[] allocation2 = new Byte[2*_1mb];

        Byte[] allocation3 = new Byte[2*_1mb];

        Byte[] allocation4 = new Byte[4*_1mb];

    }
}


result:

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
	at controller.TestJVmRiZHI.main(TestJVmRiZHI.java:24)


[GC (Allocation Failure) [DefNew: 2540K->770K(9216K), 0.0034872 secs][Tenured: 8192K->8961K(10240K), 0.0071963 secs] 10732K->8961K(19456K), [Metaspace: 3385K->3385K(1056768K)], 0.0107478 secs] [Times: user=0.01 sys=0.00, real=0.01 secs] 

[Full GC (Allocation Failure) [Tenured: 8961K->8943K(10240K), 0.0073261 secs] 8961K->8943K(19456K), [Metaspace: 3385K->3385K(1056768K)], 0.0073536 secs] [Times: user=0.02 sys=0.00, real=0.01 secs] 

Heap
 def new generation   total 9216K, used 410K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)

eden space 8192K,   5% used [0x00000000fec00000, 0x00000000fec66800, 0x00000000ff400000)

  from space 1024K,   0% used [0x00000000ff500000, 0x00000000ff500000, 0x00000000ff600000)

  to   space 1024K,   0% used [0x00000000ff400000, 0x00000000ff400000, 0x00000000ff500000)

 tenured generation   total 10240K, used 8943K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)

   the space 10240K,  87% used [0x00000000ff600000, 0x00000000ffebbd38, 0x00000000ffebbe00, 0x0000000100000000)

Metaspace       used 3429K, capacity 4494K, committed 4864K, reserved 1056768K
 
class space    used 382K, capacity 386K, committed 512K, reserved 1048576