JVM -XX:MaxDirectMemorySize

-XX:MaxDirectMemorySize

该参数指定了DirectByteBuffer能分配的空间的限额，如果没有显示指定这个参数启动jvm，默认值是xmx对应的值。

DirectByteBuffer对象是一种典型的”冰山对象”

“iceberg objects” such as a Java heap leak. A Java heap
leak from iceberg objects is when you have small leaking objects on the Java heap with
links to resources on the native heap which could cause the native heap to run out of
memory.
在堆中存在少量的泄露的对象，但其下面连接用堆外内存，这种情况容易造成内存的大量使用而得不到释放

-XX:+DisableExplicitGC

参考

http://hllvm.group.iteye.com/group/topic/27945