gc/TestSystemGC.java fails on my system like this:

$ CONF=linux-x86_64-server-fastdebug make test TEST=gc/TestSystemGC.java TEST_VM_OPTS="-XX:+UseZGC"
...

STDOUT:
[0.026s][error][gc] Failed to commit memory (Not enough space)
[0.026s][error][gc] Failed to commit memory (Not enough space)
[0.026s][error][gc] Failed to commit memory (Not enough space)
[0.026s][error][gc] Failed to commit memory (Not enough space)
[0.026s][error][gc] Forced to lower max Java heap size from 1006M(100%) to 784M(78%)
[0.026s][error][gc] Failed to allocate initial Java heap (1006M)
STDERR:
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.

Started with JDK-8269077.

The system where it fails has 1G hugetlbfs configured:

HugePages_Total: 512
HugePages_Free: 512
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 2048 kB
Hugetlb: 1048576 kB

This looks enough for G1 and other GCs to work, but apparently not for ZGC. Adding -Xmx128m makes the test pass with ZGC.