紧急问题 在ibm aix 设置java启动内存问题！？

我是这样设置启动脚本的 java -Xms512m -Xmx5120m -classpath "$lib_path/hbtool.jar:$lib_path/dom4j-1.6.jar:$lib_path/classes12.jar:$lib_path/log4j-1.2.12.jar:
$lib_path/commons-logging.jar:$lib_path/framework.jar:$lib_path/drools-ant-4.0.3.jar:$lib_path/drools-compiler-4.0.3.jar:$lib_path/d
rools-core-4.0.3.jar:$lib_path/drools-decisiontables-4.0.3.jar:$lib_path/drools-jsr94-4.0.3.jar:$lib_path/ant-1.6.5.jar:$lib_path/an
t-nodeps-1.6.5.jar:$lib_path/antlr-runtime-3.0.jar:$lib_path/core-3.2.3.v_686_R32x.jar:$lib_path/janino-2.5.7.jar:$lib_path/jsr94-1.
1.jar:$lib_path/jxl-2.4.2.jar:$lib_path/mvel14-1.2rc4rv908.jar:$lib_path/xercesImpl-2.4.0.jar:$lib_path/xml-apis-1.0.b2.jar:$lib_pat
h/xpp3_min-1.1.3.4.O.jar:$lib_path/xstream-1.2.2.jar:$class_path" com.nl.exactmkt.drools.sc.ExactMKTRule
启动之后 运行一段时间就会发生
JVMST109: Insufficient space in Javaheap to satisfy allocation request
java.lang.OutOfMemoryError: JVMXE006:OutOfMemoryError, stAllocArray for executeJava failed
        at oracle.net.ns.Packet.createBuffer(Unknown Source)
        at oracle.net.ns.DataPacket.initialize(Unknown Source)
        at oracle.net.ns.DataPacket.<init>(Unknown Source)
JVMST109: Insufficient space in Javaheap to satisfy allocation request
        at oracle.net.ns.DataPacket.<init>(Unknown Source)
问问大家这个问题 为什么会发生！