Common Pytorch Memory Management Strategies

Supercharge Your Model Training: Essential Techniques and Tricks 🚀 Are you tired of long model training times and inefficient training process? I have always struggled to understand which techniques can be chained together towards cumulative improvement and the order of magnitude improvement from each. Here is an array of powerful techniques to accelerate training with their effect size. The key in most cases is to know the memory architecture for the GPU  💾 and utilize it optimally by reducing data movement between on chip registers, cache, and off chip high-bandwidth memory. Frameworks like PyTorch make this pretty simple allowing you to do this in a few lines of code at most. - Switch to Mixed Precision: 🔢 Implementing bfloat16 can lead to a potential 3x speedup by reducing the amount of data transferred, thus enabling larger batch sizes. Although GPUs may promise up to an 8x improvement, actual gains could be lower due to memory constraints. Benchmarking is essential! - PyTorch Compile: 🖥️ Experience about a 2.5x speed increase by minimizing unnecessary memory bus traffic. This approach prepares your computations for more efficient execution. - Flash Attention: ⚡ Utilize a fused kernel specifically optimized for attention-heavy models, which can boost performance by up to 40% by enhancing memory hierarchy utilization. - Optimized Data Formats: 📊 Aligning your vocab size to a power of 2 can provide a straightforward 10% speed boost by improving memory access efficiency. - Hyperparameter Tuning: 🛠️ Gain an additional 5-10% speed by tweaking hyperparameters and employing fused kernels for optimizers like AdamW. Bespoke Fused Kernels: 🧩 Push the boundaries with custom kernels designed specifically for your model’s architecture to achieve optimal performance. Leverage Additional Optimizations: ➕ Employ vector operations (e.g., AVX-512) on CPUs or use sparse kernels for pruned models to further enhance memory efficiency. Scale Responsibly: 📈 Before moving to a multi-GPU setup, ensure you've maximized the potential of single-GPU optimizations to avoid inefficiencies. Once your setup is optimized, scaling across multiple GPUs can dramatically reduce training times by parallelizing the workload and minimizing data transfers. You can do this almost trivially by using things like Hugging Face Accelerate. Remember, the effectiveness of these techniques can vary based on your specific model, hardware setup, and other variables. Extensive benchmarking is crucial to find the perfect balance between speed and accuracy. Optimization is a continuous journey. Stay proactive in exploring new methods to reduce training times and remain competitive in the fast-evolving field of machine learning. For more insights, check out Karpathy’s latest video where he replicates GPT-2 on 8x A100s, astonishingly beating GPT-3 on Hellaswag. It’s incredible to see such advancements, allowing what once took months to be accomplished virtually overnight. 🌙✨

My next tutorial on pretraining an LLM from scratch is now out. It starts with a step-by-step walkthrough of understanding, calculating, and optimizing the loss. After training, we update the text generation function with temperature scaling and top-k sampling. And finally, we also load openly available pretrained weights into our scratch-built model architecture. Along with this pretraining tutorial, I also have bonus material on speeding up the LLM training. These apply not just to LLMs but also to other transformer-based models like vision transformers: 1. Instead of saving the causal mask, this creates the causal mask on the fly to reduce memory usage (here it has minimal effect, but it can add up in long-context size models like Llama 3.2 with 131k-input-tokens support) 2. Use tensor cores (only works for Ampere GPUs like A100 and newer) 3. Use the fused CUDA kernels for `AdamW` by setting 4. Pre-allocate and re-use GPU memory via the pinned memory setting in the data loader 5. Switch from 32-bit float to 16-bit brain float (bfloat16) precision 6. Replace from-scratch implementations of attention mechanisms, layer normalizations, and activation functions with PyTorch counterparts that have optimized CUDA kernels 7. Use FlashAttention for more efficient memory read and write operations 8. Compile the model 9. Optimize the vocabulary size 10. After saving memory with the steps above, increase the batch size Video tutorial: https://lnkd.in/gDRycWea PyTorch speed-ups: https://lnkd.in/gChvGCJH

Running PyTorch in production? Memory is most like an issue and also a silent bottleneck. I came across this blog that shows how they slashed inference latency and costs using lesser-known tricks. Here’s what stood out: 👉 Selective Gradient Checkpointing Checkpoint only memory-heavy layers → cuts peak memory by 40%. 👉 Dynamic Kernel Caching Cache common input shapes during warmup → avoids CUDA recompilation lag. 👉 Manual Precision Casting Control which tensors stay in FP32 vs. BF16 → stability + speed. 👉 Smart empty_cache() Scheduling Call it only during idle windows → avoids perf drops. 👉 Partial Quantization Quantize only safe layers like linear → preserve accuracy, save memory. 👉 Custom CUDA Streams Overlap compute and data loads → reduces GPU idle time. 👉 Shared Memory Tensors Zero-copy multiprocessing → boosts throughput for high RPS services. These aren’t just dev tips — they’re real production survival tactics. Full blog here - https://lnkd.in/gzJSccc8