[SOLVED] Why I cannot set my java program with expected memory size?

Why I cannot set my java program with expected memory size?

I limit my java program with -Xmx2g -Xmn1280m -Xms2g -XX:MetaspaceSize=128m -XX:MaxMetaspaceSize=152m -XX:SurvivorRatio=8 -XX:+UseConcMarkSweepGC.
And then, I use top to show memory uesage, which shows:

Tasks: 139 total,   1 running, 138 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.5 us,  0.9 sy,  0.2 ni, 98.4 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem :  7896536 total,  2724188 free,  1870168 used,  3302180 buff/cache
KiB Swap:        0 total,        0 free,        0 used.  5756128 avail Mem 

   PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND                                                  
 69518 service   20   0 4089960   1.5g  16916 S   1.3 19.3   3:03.27 java

The real memory uesage is 1.5g.
But I have already set the jvm heap size.
Why this happened? Thank you very much.

Solution

Java heap memory and stack memory are virtual memory.
VIRT is the virtual memory space: the sum of everything in the virtual memory map.
RES is the resident set size: the number of pages that are currently resident in RAM.
In short, parameters above just affects the virtual memory.