On some linux x86_64 machine we run in the test “jdk/internal/platform/cgroup/TestCgroupMetrics.java” into this
  NumberFormatException :
 
java.lang.NumberFormatException: For input string: "18446744073709551615"
at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:68)
at java.base/java.lang.Long.parseLong(Long.java:699)
at java.base/java.lang.Long.parseLong(Long.java:824)
at jdk.test.lib.containers.cgroup.MetricsTester.getLongValueFromFile(MetricsTester.java:160)
at jdk.test.lib.containers.cgroup.MetricsTester.testMemorySubsystem(MetricsTester.java:223)
at TestCgroupMetrics.main(TestCgroupMetrics.java:50)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:567)
at com.sun.javatest.regtest.agent.MainWrapper$MainThread.run(MainWrapper.java:127)
at java.base/java.lang.Thread.run(Thread.java:830)

I checked the number "18446744073709551615" and it seems to be larger than Long.html#MAX_VALUE : A constant holding the maximum value a long can have, 2^63-1 = “9,223,372,036,854,775,807”
But we have : "18,446,744,073,709,551,615" .

Looks like from C side (Linux kernel?) we have unsigned long long.
https://www.redhat.com/archives/libvir-list/2013-December/msg00435.html
describes it a bit.