Strategies for Memory Optimization in PyTorch
1. Use torch.no_grad()
for Inference
During inference or evaluation, gradient calculations are unnecessary. Using torch.no_grad()
reduces memory consumption by not storing gradients. This can significantly reduce the amount of memory used during the inference phase.
with torch.no_grad():
outputs = model(inputs)
2. Clear Unused Variables
Use del to delete variables that are no longer needed. This frees up memory that can be used by other parts of the program. By deleting the loss and outputs tensors after each training step, you can prevent memory from being unnecessarily occupied.
loss = criterion(outputs, targets)
loss.backward()
optimizer.step()
del loss, outputs
3. Use ‘inplace'
Operations
Many PyTorch operations have an in-place version, which can save memory by modifying existing tensors instead of creating new ones. In-place operations are usually indicated by a trailing underscore in PyTorch (e.g., add_).
x = x.add_(y) # In-place addition
4. Optimize Data Loading
Efficient data loading can reduce memory overhead. Use pin_memory=True
for faster data transfer to GPU, and choose appropriate batch sizes to balance memory usage and computational efficiency.
train_loader = DataLoader(dataset, batch_size=64, shuffle=True, pin_memory=True)
5. Gradient Accumulation
For large models, training with small batches can reduce memory usage. Accumulate gradients over multiple mini-batches before updating the model weights. This technique allows you to effectively increase the batch size without requiring additional memory.
optimizer.zero_grad()
for i, (inputs, targets) in enumerate(train_loader):
outputs = model(inputs)
loss = criterion(outputs, targets)
loss.backward()
if (i+1) % accumulation_steps == 0:
optimizer.step()
optimizer.zero_grad()
6. Model Checkpointing
Save intermediate model states and reload them when necessary to avoid keeping the entire model in memory. This can be particularly useful for long-running training processes or when experimenting with different model configurations.
torch.save(model.state_dict(), 'model_checkpoint.pth')
model.load_state_dict(torch.load('model_checkpoint.pth'))
7. Half-Precision Training (Mixed Precision)
Training with mixed precision (using both 16-bit and 32-bit floating point) can significantly reduce memory usage while maintaining model accuracy. The torch.cuda.amp
module provides tools to easily implement mixed precision training.
from torch.cuda.amp import GradScaler, autocast
scaler = GradScaler()
for inputs, targets in train_loader:
optimizer.zero_grad()
with autocast():
outputs = model(inputs)
loss = criterion(outputs, targets)
scaler.scale(loss).backward()
scaler.step(optimizer)
scaler.update()
8. Remove Detached Graphs
Avoid retaining computational graphs when they are no longer needed. Use .detach()
to create a tensor that shares storage with its base tensor but does not require gradient computation.
outputs = model(inputs)
detached_outputs = outputs.detach()
9. Efficient Memory Allocation
Preallocate memory for frequently used tensors and reuse them to avoid frequent memory allocation and deallocation. This can help in reducing fragmentation and improving memory utilization.
buffer = torch.empty(buffer_size, device=device)
10. Profiling and Monitoring
Use PyTorch’s built-in tools like torch.cuda.memory_summary()
and third-party libraries like torchsummary
to profile and monitor memory usage. This helps in identifying memory bottlenecks and optimizing memory allocation.
print(torch.cuda.memory_summary())
How to optimize memory usage in PyTorch?
Memory optimization is essential when using PyTorch, particularly when training deep learning models on GPUs or other devices with restricted memory. Larger model training, quicker training periods, and lower costs in cloud settings may all be achieved with effective memory management. This article describes how to minimize memory utilization in PyTorch, covers key topics, and offers useful code samples.
Table of Content
- Understanding Memory Consumption in PyTorch
- Strategies for Memory Optimization in PyTorch
- 1. Use torch.no_grad() for Inference
- 2. Clear Unused Variables
- 3. Use ‘inplace’ Operations
- 4. Optimize Data Loading
- 5. Gradient Accumulation
- 6. Model Checkpointing
- 7. Half-Precision Training (Mixed Precision)
- 8. Remove Detached Graphs
- 9. Efficient Memory Allocation
- 10. Profiling and Monitoring
- Conclusion