PyTorch optimizer

Explore how ApexW optimizes PyTorch for larger GPU workloads

Most PyTorch optimizers treat memory like it's infinite, but anyone training large models knows that's not reality.

4 min readMachine Learning

ApexW is the kind of project that deserves attention not because it claims to reinvent deep learning, but because it respects the constraints you actually hit in production. The developer's honest framing, that this is an engineering trade-off rather than a magic bullet, is exactly the mindset more optimizer work should adopt. Cutting optimizer-state memory in half while gaining a 1.5x speedup on large-tensor workloads is a meaningful win for anyone who has stared down an out-of-memory error during model fine-tuning. The reality check on small-tensor workloads, where Python launch latency makes the Triton path roughly 0.21x as fast as PyTorch native, is just as valuable. That kind of transparency builds trust, and it gives practitioners the information they need to decide when ApexW is worth testing.

The practical implications here connect directly to the broader challenge of scaling models on fixed hardware. If you are training Transformers or fine-tuning large language models, the optimizer state often competes with batch size for precious GPU memory. A tool that halves that state lets you increase batch size or scale model parameters without upgrading your infrastructure. That is not a theoretical benefit; it is a concrete lever for productivity. The developer's own end-to-end MLP test shows PyTorch still runs slightly faster overall due to deeper C++ integration, so the win is not universal yet. But for workloads dominated by a few large tensors, the optimizer step itself becomes a bottleneck worth attacking. This aligns with the ongoing push to simplify multi-GPU training and tune batch sizes automatically, where memory efficiency directly influences how far you can stretch existing resources. Similarly, the broader quest to make AI more accessible, whether through repurposing drugs or mastering noisy data, ultimately depends on tools that lower the barrier to experimentation. ApexW is a small but genuine step in that direction.

The honest caveats matter more than the headline numbers. The developer is clear that the speedup does not consistently hold in automatic execution mode, and that full training steps are dominated by forward and backward passes. That means the 1.5x figure is best understood as a component-level improvement, not a guarantee of faster wall-clock training. The real question for the community is whether the compact-state approach can be extended to handle small-tensor layouts without the Python overhead penalty. The current 76.0 ms/step versus 16.1 ms/step on the many-small test is a stark reminder that kernel-level optimizations only pay off when launch overhead does not eat the gains. This is exactly the kind of trade-off that needs a second pair of eyes, and the developer's request for feedback on both implementation and benchmarks is the right call.

What we want to see next is a benchmark on a realistic model, something like a moderate-sized Transformer, with full training loop measurements and memory tracking across different GPU generations. That would tell us whether the memory savings translate into meaningful batch size increases without sacrificing throughput. The developer has already identified the right next steps, and the community should engage with the code rather than dismiss it for its current limitations. The specific takeaway is straightforward: if you are hitting OOM barriers on large-tensor workloads, ApexW's compact optimizer state is worth a test run, but verify it against your own model architecture before trusting the 1.5x number. The future of this project depends on whether it can close the small-tensor gap and prove itself in end-to-end training. That is the benchmark worth watching.

From Machine Learning

Hey, I've been working on a PyTorch optimizer called ApexW and figured I'd share it here to get some feedback from people who know more about this stuff than I do.

The main goal is to reduce optimizer-state memory usage and see how much faster I can make optimizer steps on larger GPU workloads. I've been experimenting with compact optimizer states and a Triton-based execution path.

Read the original at Machine Learning