This Oracle HotSpot option affects the alignment of direct byte buffer allocation and is implemented by the Eclipse 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.
For more information about the changes, see RFE 4837564, which was introduced in the Java SE 7 release notes.