Hi, I have configured MPICH 4.1.2 with both -with-device=ch4:ofi and -with-device=ch4:ucx. My application fails in both cases when it can't allocate enough memory. For -with-device=ch4:ofi : Unable to create send CQ of size 5080 on mlx5_0: Cannot allocate memory n001.cluster.pssclabs.com:rank0.NeedlesMpiMM: Unable to initialize verbs NIC /sys/class/infiniband/mlx5_0 (unit 0:0) n001.cluster.pssclabs.com:rank0: PSM3 can't open nic unit: 0 (err=23) Abort(606197135): Fatal error in internal_Init: Other MPI error, error stack: internal_Init(66)........: MPI_Init(argc=0x7ffc1cbd334c, argv=0x7ffc1cbd3340) failed MPII_Init_thread(234)....: MPID_Init(513)...........: MPIDI_OFI_init_local(604): create_vni_context(982)..: OFI endpoint open failed (ofi_init.c:982:create_vni_context:Cannot allocate memory) Configuring using -with-device=ch4:ucx, there was a very similar error involving /sys/class/infiniband/mlx5_0 that explicitly stating that the locked memory limit (ulimit -l) needs to be set to "unlimited". Are there any other ch4 device configuration options that don't require unlimited locked memory? Thanks, Kurt