How to Fix RuntimeError: cuda error: an illegal memory access was encountered

The RuntimeError: cuda error: an illegal memory access was encountered error occurs when an issue accessing GPU memory in your CUDA application.

The error suggests an out-of-bound memory access similar to a segfault on the CPU, like an indexing error in the low-level code.

Sometimes RuntimeError occurs on the large batch size. It does not occur on smaller batch sizes. The peak memory usage might have caused the OOM issue.


  1.  If the memory you are accessing has already been freed.
  2. If you are trying to access memory outside the bounds of an array.
  3. Incorrect device-to-host or host-to-device data transfers.
  4. Trying to read or write to read-only or write-only memory.

How to Fix RuntimeError: cuda error: an illegal memory access was encountered

To fix the RuntimeError: cuda error: an illegal memory access was encountered, set a specific GPU using the device = torch.cuda.set_device(1) function instead of device = torch.device(“cuda:1”) function.

The code device = torch.cuda.set_device(1) sets the current CUDA device used by PyTorch to be the GPU with index 1.

PyTorch supports multiple GPUs, and the set_device() function is used to specify which GPU should be used for computations.

Alternate solutions

  1. You can check the memory allocation and access patterns in your code.
  2. You must ensure proper synchronization of host and device memory operations.
  3. You need to use the CUDA profiler to inspect memory access patterns.
  4. Consider using tools for memory debugging, such as cuda-memcheck.
  5. You need to verify compatibility issues with the GPU driver and CUDA version.

After considering all the proposed solutions, one solution might work for you.

CUDA is a parallel computing platform and programming model created by NVIDIA

CUDA has been widely adopted across consumer and industrial ecosystems to accelerate high-performance computing (HPC) and research applications.

I hope this will help you resolve your error.

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.