GC 测试

App

public class GCApp {
    // 1 MB = 1024 KB, 1 KB = 1024 B(字节), 1 B=8 b(bit比特)
    public static final int MB = 1024 * 1024;

    public static void main(String[] args) {
        byte[] a1, a2, a3, a4;
        a1 = new byte[2 * MB];
        a2 = new byte[2 * MB];
        a3 = new byte[2 * MB];
        a4 = new byte[4 * MB];
    }
}

vm option

-verbose:gc
-Xms20m
-Xmx20m
-Xmn10M
-XX:+PrintGCDetails
-XX:SurvivorRatio=8

Heap
 PSYoungGen      total 9216K, used 8155K [0x00000007bf600000, 0x00000007c0000000, 0x00000007c0000000)
  eden space 8192K, 99% used [0x00000007bf600000,0x00000007bfdf6fe8,0x00000007bfe00000)
  from space 1024K, 0% used [0x00000007bff00000,0x00000007bff00000,0x00000007c0000000)
  to   space 1024K, 0% used [0x00000007bfe00000,0x00000007bfe00000,0x00000007bff00000)
 ParOldGen       total 10240K, used 4096K [0x00000007bec00000, 0x00000007bf600000, 0x00000007bf600000)
  object space 10240K, 40% used [0x00000007bec00000,0x00000007bf000010,0x00000007bf600000)
 Metaspace       used 3192K, capacity 4496K, committed 4864K, reserved 1056768K
  class space    used 355K, capacity 388K, committed 512K, reserved 1048576K