jax-smi

JAX Synergistic Memory Inspector

jax-smi is a tool for real-time inspection of the memory usage of a JAX process. It is similar to nvidia-smi for GPU, but works on multiple platforms including CPU, GPU and TPU.

On TPU platforms, jax-smi is the only way to monitor TPU memory usage. On GPU platforms, jax-smi is also preferable to nvidia-smi. The latter is unable to report real-time memory usage of JAX processes, as JAX always pre-allocates 90% of the GPU memory by default.

This project is supported by Cloud TPUs from Google's TPU Research Cloud (TRC).

Installation

Install go. On Ubuntu, this is usually done by:

sudo apt-get install golang

If you followed tpu-starter to set up the TPU environment, go should be already installed.

Then install jax-smi with:

pip install jax-smi

Usage

In your JAX script:

from jax_smi import initialise_tracking
initialise_tracking()
# some computation...

Open a shell and run:

jax-smi

Approach

Save the memory profile to /dev/shm/memory.prof in a separate thread every 1 second using jax.profiler.save_device_memory_profile().

Inspect the memory profile with go tool pprof -tags /dev/shm/memory.prof.

See https://twitter.com/ayaka14732/status/1565013139594551296 for more details.

Limitations

Tracing can only be performed by one process at a time. If tracing is performed by multiple JAX processes, they will write the memory profiles to the same file, which will lead to conflicts.

The jax-smi command line tool cannot detect if a memory profile file is out of date. Therefore, even if no JAX process is running, the tool will still read the outdated memory profile and report outdated memory usage information.