Using small heap sizes is currently broken on systems with a large pages size. E.g. with 64k Pages on PPC64:
java -XX:+PrintFlagsFinal -Xmx8m -version |grep -E "GCCardSizeInBytes|MaxHeapSize"
     uint GCCardSizeInBytes = 512 {product} {default}
   size_t MaxHeapSize = 33554432 {product} {command line, ergonomic}
   size_t SoftMaxHeapSize = 33554432 {manageable} {ergonomic}

Some tests don't work as expected because of a much larger MaxHeapSize on such systems. See JDK-8339166 for example.

Root cause is that the MaxHeapSize gets increased dependent on GCCardSizeInBytes * os::vm_page_size() in GCArguments::compute_heap_alignment().