Bug 309554

--1491-- WARNING: unhandled syscall: 216
--1491-- You may be able to write your own handler.
--1491-- Read the file README_MISSING_SYSCALL_OR_IOCTL.
--1491-- Nevertheless we consider this a bug.  Please report
--1491-- it at http://valgrind.org/support/bug_reports.html.

Valgrind doesn't support the remap_file_pages syscall which is e.g. useful for easy-to-use and fast ringbuffers (you can have arbitrary-sized reads and writes at arbitrary positions in the ringbuffer without having to constantly think about when some pointer wraps by mapping to adjacent areas of virtual memory to the same physical memory section).