看到一篇文章说，系统进程内存最大限制，32位和64位理论上最大都可达到4G，这个最大限制可以测试，用类似于下面命令：

 java -Xmx503446m -version
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如果不报错，说明能分配500G左右
我试了一下，

$ java -Xmx603446m -version 
Java HotSpot(TM) 64-Bit Server VM warning: INFO:         
os::commit_memory(0x00007e6915650000, 19773718528, 0) failed; 
error='Cannot allocate memory' (errno=12)
#
# There is insufficient memory for the Java Runtime Environment 
to continue.
# Native memory allocation (mmap) failed to map 19773718528 
bytes for committing reserved memory.
$ java -Xmx503446m -version 
java version "1.8.0_131"
Java(TM) SE Runtime Environment (build 1.8.0_131-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.131-b11, mixed mode)
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可见500G左右没问题，600G就不行了,但是这个远超4G了？