MPI memory leak

Question

I am writing some code that uses MPI and I was keeping noticing some memory leaks when running it with valgrind. While trying to identify where the problem was, I ended up w

Answer 1

The OpenMPI FAQ addresses issues with valgrind. This refers initalization issues and memory leaks during finalization - which should have no practical negative impact.

There are many situations, where Open MPI purposefully does not initialize and subsequently communicates memory, e.g., by calling writev. Furthermore, several cases are known, where memory is not properly freed upon MPI_Finalize.

This certainly does not help distinguishing real errors from false positives. Valgrind provides functionality to suppress errors and warnings from certain function contexts.

In an attempt to ease debugging using Valgrind, starting with v1.5, Open MPI provides a so-called Valgrind-suppression file, that can be passed on the command line:

mpirun -np 2 valgrind
--suppressions=$PREFIX/share/openmpi/openmpi-valgrind.supp

Answer 2

You're not doing anything wrong. Memcheck false positives with valgrind are common, the best you can do is suppress them.

This page of the manual speaks more about these false positives. A quote near the end:

The wrappers should reduce Memcheck's false-error rate on MPI applications. Because the wrapping is done at the MPI interface, there will still potentially be a large number of errors reported in the MPI implementation below the interface. The best you can do is try to suppress them.