Unified memory -gpu=unified

Dear All,
I tried using unified memory via the -gpu=unified switch in nvc++ from hpc_sdk 24.3. I’m running a Debian 12 (bookworm) on a Laptop with an Ampere A1000 graphic card. My examples run fine without that switch, however, as soon as I add -gpu=unified to the nvc++ compilation, the code compiles, however I get the following message when running the code:

Accelerator Fatal Error: The application was compiled with -gpu=unified, but this platform does not support Unified Memory.
Please consult the NVIDIA HPC Compilers User's Guide for details.

To best of my knowledge ( well what I could find on the internet) the Ampere card should be compatible with unified memory. Is there anything special one hast to install?, or do I misunderstand the documentation and unified memory should not work for the Ampere card?

Best regards,
Peter

Hi Peter,

There’s two types of CUDA Unified Memory. The older “-gpu=managed” version which will work on your system, and the newer full UM “-gpu=unified” which requires Heterogeneous Memory Management (HMM) enabled in a newer Linux Kernel (6.1.24+, 6.2.11+, or 6.3+)

The key difference is that “managed” is only available for allocated heap memory while “unified” adds support for global and stack memory.

Full details on HMM please see:

I did find this post asking about enabling HMM on Debian 12, but unfortunately there wasn’t a response. The Debian 2 pages just indicate that kernel 6.1 is used, but I don’t know which build or if it supports HMM. Our lab uses Ubuntu 22.04 with 6.2.35.

The following article may also be helpful, though focuses on GH200.

-Mat

Dear Mat,
thanks for your explanation, I’ll contact our sysadmin concerning HMM.
Best regards,
Peter

Dear Mat,
for your information, on Debian bookworm the latest backported kernel seems to be 6.6.13 with NVIDIA UNIX Open Kernel Module for x86_64 525.147.05. For 535 we would have to switch to debian unstable. Seems like I’ll have to wait a little bit.
Best regards,
Peter

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