6. Advanced Memory Checking Frameworks for MPI Parallel Applications in Open MPI

In this paper, we describe the implementation of memory checking functionality that is based on instrumentation tools. The combination of instrumentation based checking functions and the MPI-implementation offers superior debugging functionalities, for errors that otherwise are not possible to detect with comparable MPI-debugging tools. Our implementation contains three parts: first, a memory callback extension that is implemented on top of the Valgrind Memcheck tool for advanced memory checking in parallel applications; second, a new instrumentation tool was developed based on the Intel Pin framework, which provides similar functionality as Memcheck it can be used in Windows environments that have no access to the Valgrind suite; third, all the checking functionalities are integrated as the so-called memchecker framework within Open MPI. This will also allow other memory debuggers that offer a similar API to be integrated. The tight control of the user’s memory passed to Open MPI, allows us to detect application errors and to track bugs within Open MPI itself. The extension of the callback mechanism targets communication buffer checks in both pre- and post-communication phases, in order to analyze the usage of the received data, e.g. whether the received data has been overwritten before it is used in an computation or whether the data is never used. We describe our actual checks, classes of errors being found, how memory buffers are being handled internally, show errors actually found in user’s code, and the performance implications of our instrumentation.