Java8 MetaspaceSize flag not working - java-8

Question

I have a simple test code that setup both -XX:MetaspaceSize and -XX:MaxMetaspaceSize to a same value. I think the metaspace then should not dynamically resizing. But from my testing (check Metaspace diagram from VisualVM GC and print out log by jstat), i saw metaspace keep growing from a low value to the max value i set. So doesn't the -XX:MetaspaceSize not working?
My testing code:
try {
while(true){
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(A.class);
enhancer.setUseCache(false);
enhancer.setCallback((MethodInterceptor) (obj, method, args1, methodProxy) -> methodProxy.invokeSuper(obj, args1));
enhancer.create();
Thread.sleep(50);
}
} catch (Throwable throwable) {
throwable.printStackTrace();
}
VM args:
-XX:MetaspaceSize=10m -XX:MaxMetaspaceSize=10m
Java version:
java version "1.8.0_45"
Java(TM) SE Runtime Environment (build 1.8.0_45-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.45-b02, mixed mode)
jstat result: (MC value keep growing to around 10m)
C:\Users\dyu>jstat -gc 12336 1000 20
S0C S1C S0U S1U EC EU OC OU MC MU CCSC CCSU YGC YGCT FGC FGCT GCT
8192.0 8192.0 0.0 2207.8 49152.0 43399.2 131072.0 16.0 7168.0 6777.9 768.0 677.7 1 0.015 0 0.000 0.015
8192.0 8192.0 0.0 2207.8 49152.0 48166.1 131072.0 16.0 7168.0 6777.9 768.0 677.7 1 0.015 0 0.000 0.015
8192.0 8192.0 2592.0 0.0 49152.0 3691.9 131072.0 24.0 8832.0 8403.6 896.0 795.9 2 0.020 0 0.000 0.020
8192.0 8192.0 2592.0 0.0 49152.0 7537.9 131072.0 24.0 8832.0 8403.6 896.0 795.9 2 0.020 0 0.000 0.020
8192.0 8192.0 2592.0 0.0 49152.0 11378.9 131072.0 24.0 8832.0 8403.6 896.0 795.9 2 0.020 0 0.000 0.020
8192.0 8192.0 2592.0 0.0 49152.0 16180.3 131072.0 24.0 8832.0 8403.6 896.0 795.9 2 0.020 0 0.000 0.020
8192.0 8192.0 2592.0 0.0 49152.0 20021.3 131072.0 24.0 8832.0 8403.6 896.0 795.9 2 0.020 0 0.000 0.020
8192.0 8192.0 2592.0 0.0 49152.0 24822.5 131072.0 24.0 8832.0 8403.6 896.0 795.9 2 0.020 0 0.000 0.020
8192.0 8192.0 2592.0 0.0 49152.0 28663.5 131072.0 24.0 8832.0 8403.6 896.0 795.9 2 0.020 0 0.000 0.020
8192.0 8192.0 2592.0 0.0 49152.0 33466.8 131072.0 24.0 8832.0 8403.6 896.0 795.9 2 0.020 0 0.000 0.020
8192.0 8192.0 2592.0 0.0 49152.0 37312.8 131072.0 24.0 8832.0 8403.6 896.0 795.9 2 0.020 0 0.000 0.020
8192.0 8192.0 2592.0 0.0 49152.0 42114.1 131072.0 24.0 8832.0 8403.6 896.0 795.9 2 0.020 0 0.000 0.020
8192.0 8192.0 2592.0 0.0 49152.0 45955.1 131072.0 24.0 8832.0 8403.6 896.0 795.9 2 0.020 0 0.000 0.020
8192.0 8192.0 0.0 3488.0 49152.0 1925.1 131072.0 32.0 10752.0 10225.1 1024.0 934.2 3 0.026 0 0.000 0.026
8192.0 8192.0 0.0 3488.0 49152.0 6737.6 131072.0 32.0 10752.0 10225.1 1024.0 934.2 3 0.026 0 0.000 0.026
8192.0 8192.0 0.0 3488.0 49152.0 11758.5 131072.0 32.0 10752.0 10225.1 1024.0 934.2 3 0.026 0 0.000 0.026
8192.0 8192.0 0.0 3488.0 49152.0 15608.7 131072.0 32.0 10752.0 10225.1 1024.0 934.2 3 0.026 0 0.000 0.026
8192.0 8192.0 0.0 3488.0 49152.0 29056.4 131072.0 32.0 10752.0 10225.1 1024.0 934.2 3 0.026 0 0.000 0.026
8192.0 8192.0 0.0 3488.0 49152.0 34196.6 131072.0 32.0 10752.0 10225.1 1024.0 934.2 3 0.026 0 0.000 0.026
8192.0 8192.0 0.0 3488.0 49152.0 39339.7 131072.0 32.0 10752.0 10225.1 1024.0 934.2 3 0.026 0 0.000 0.026

Answer 1

You have misunderstood what -XX:MetaspaceSize does:
-XX:MetaspaceSize=size
Sets the size of the allocated class metadata space that will trigger a garbage collection the first time it is exceeded. This threshold for a garbage collection is increased or decreased depending on the amount of metadata used.
The name of that option might be considered misleading, unless you interpret it as “intended size”, so obviously it should trigger garbage collection when exceeded (while max size defines the hard limit).
There is an open bug report, JDK-8067205 calling for an option to set the initial metaspace size.