This Oracle HotSpot option affects the alignment of direct byte buffer allocation and is implemented by the OpenJ9 VM for compatibility.
As discussed in the Oracle documentation, before Java™ SE 7, direct buffers that were allocated using
java.nio.ByteBuffer.allocateDirect(int) were aligned on a page boundary. This behavior changed in Java SE 7 and the
-XX:+PageAlignDirectMemory option is provided to revert to the previous behavior.