I am using Mfix 23.3.2. I have installed it on Ubuntu 22.04.3 LTS. When using DMP, the solver runs and it seems to speed up the run as expected. However, I get the error as shown in the attached image. What is this and what do I do about it?
This is a bit beyond the scope of MFiX - if you search for cma-permission-denied you will find more about this. See for example users@lists.openhpc.community | OpenMPI and shared memory
The full text of the cma-permission-denied message is:
[cma-permission-denied]
WARNING: Linux kernel CMA support was requested via the
btl_vader_single_copy_mechanism MCA variable, but CMA support is
not available due to restrictive ptrace settings.
The vader shared memory BTL will fall back on another single-copy
mechanism if one is available. This may result in lower performance.
CMA stands for Cross-memory attach. The vader is the name for the mechanism used in OpenMPI for sharing memory. OpenMPI is telling you that it is trying to use a particular mechanism, which is not allowed, and is falling back on another strategy which may be slower. It’s possible that this message is entirely harmless, but it’s also possible that you will get better performance with CMA.
To allow ptrace, do
# echo 0 > /proc/sys/kernel/yama/ptrace_scope
and to make that configuration persist across reboots, put
kernel.yama.ptrace_scope = 0
into /etc/sysctl.conf
On the other hand, you may choose to change the value of btl_vader_single_copy_mechanism in your OpenMPI configuration, to disable this feature completely.
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Thank you for the reply