Collect MPI usage issues on new page

* Resolves #291, #270, and #163

doc.zih.tu-dresden.de/docs/jobs_and_resources/mpi_issues.md

+# Known MPI-Usage Issues
+
+This pages holds known issues observed with MPI and concrete MPI implementations.
+
+## R Parallel Library on Multiple Nodes
+
+Using the R parallel library on MPI clusters has shown problems when using more than a few compute
+nodes. The error messages indicate that there are buggy interactions of R/Rmpi/OpenMPI and UCX.
+Disabling UCX has solved these problems in our experiments.
+
+We invoked the R script successfully with the following command:
+
+```
+console mpirun -mca btl_openib_allow_ib true --mca pml ^ucx --mca osc ^ucx -np 1 Rscript
+--vanilla the-script.R
+```
+
+where the arguments `-mca btl_openib_allow_ib true --mca pml ^ucx --mca osc ^ucx` disable usage of
+UCX.
+
+## MPI Function `MPI_Win_allocate`
+
+The function `MPI_Win_allocate` is a one-sided MPI call that allocates memory and returns a window
+object for RDMA operations (ref. [man page](https://www.open-mpi.org/doc/v3.0/man3/MPI_Win_allocate.3.php)).
+
+> Using MPI_Win_allocate rather than separate MPI_Alloc_mem + MPI_Win_create may allow the MPI implementation to optimize the memory allocation.
+> (Using advanced MPI)
+
+It was observed for at least for the `OpenMPI/4.0.5` module that using `MPI_Alloc_mem` in
+conjunction with `MPI_Win_create` instead of `MPI_Win_Allocate` leads to segmentation faults in the
+calling application. To be precise, the segfaults occurred at partition `romeo` when about 200 GB
+per node where allocated. In contrast, the segmentation faults vanished when the implementation was
+refactored to call the `MPI_Win_allocate` function.

doc.zih.tu-dresden.de/mkdocs.yml

@@ -80,6 +80,7 @@ nav:
       - Compilers and Flags: software/compilers.md
       - GPU Programming: software/gpu_programming.md
       - Mathematics Libraries: software/math_libraries.md
+      - MPI Usage Issues: software/mpi_issues.md
       - Debugging: software/debuggers.md
     - Software Engineering Tools:
       - MPI Error Detection: software/mpi_usage_error_detection.md