Add checkpointing example

docs/examples/data/checkpointing/README.rst

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+Checkpointing
+=============
+
+
+**Prerequisites**
+
+Make sure to read the following sections of the documentation before using this
+example:
+
+* :ref:`pytorch_setup`
+* :ref:`001 - Single GPU Job`
+
+The full source code for this example is available on `the mila-docs GitHub
+repository.
+<https://github.com/mila-iqia/mila-docs/tree/master/docs/examples/data/checkpointing>`_
+
+
+**job.sh**
+
+.. code:: diff
+
+    # distributed/001_single_gpu/job.sh -> data/checkpointing/job.sh
+    #!/bin/bash
+    #SBATCH --gpus-per-task=rtx8000:1
+    #SBATCH --cpus-per-task=4
+    #SBATCH --ntasks-per-node=1
+    #SBATCH --mem=16G
+    #SBATCH --time=00:15:00
+   +#SBATCH --signal=B:TERM@300 # tells the controller to send SIGTERM to the job 5
+   +                            # min before its time ends to give it a chance for
+   +                            # better cleanup. If you cancel the job manually,
+   +                            # make sure that you specify the signal as TERM like
+   +                            # so scancel --signal=TERM <jobid>.
+   +                            # https://dhruveshp.com/blog/2021/signal-propagation-on-slurm/
+   +
+   +# trap the signal to the main BATCH script here.
+   +sig_handler()
+   +{
+   +    echo "BATCH interrupted"
+   +    wait # wait for all children, this is important!
+   +}
+   +
+   +trap 'sig_handler' SIGINT SIGTERM SIGCONT
+
+
+    # Echo time and hostname into log
+    echo "Date:     $(date)"
+    echo "Hostname: $(hostname)"
+
+
+    # Ensure only anaconda/3 module loaded.
+    module --quiet purge
+    # This example uses Conda to manage package dependencies.
+    # See https://docs.mila.quebec/Userguide.html#conda for more information.
+    module load anaconda/3
+    module load cuda/11.7
+
+   +
+    # Creating the environment for the first time:
+    # conda create -y -n pytorch python=3.9 pytorch torchvision torchaudio \
+   -#     pytorch-cuda=11.7 -c pytorch -c nvidia
+   +#     pytorch-cuda=11.7 scipy -c pytorch -c nvidia
+    # Other conda packages:
+    # conda install -y -n pytorch -c conda-forge rich tqdm
+
+    # Activate pre-existing environment.
+    conda activate pytorch
+
+
+    # Stage dataset into $SLURM_TMPDIR
+    mkdir -p $SLURM_TMPDIR/data
+    cp /network/datasets/cifar10/cifar-10-python.tar.gz $SLURM_TMPDIR/data/
+    # General-purpose alternatives combining copy and unpack:
+    #     unzip   /network/datasets/some/file.zip -d $SLURM_TMPDIR/data/
+    #     tar -xf /network/datasets/some/file.tar -C $SLURM_TMPDIR/data/
+
+
+    # Fixes issues with MIG-ed GPUs with versions of PyTorch < 2.0
+    unset CUDA_VISIBLE_DEVICES
+
+    # Execute Python script
+    python main.py
+
+
+**main.py**
+
+.. code:: diff
+
+    # distributed/001_single_gpu/main.py -> data/checkpointing/main.py
+    """Single-GPU training example."""
+    import logging
+    import os
+   -from pathlib import Path
+   +import shutil
+
+    import rich.logging
+    import torch
+    from torch import Tensor, nn
+    from torch.nn import functional as F
+    from torch.utils.data import DataLoader, random_split
+    from torchvision import transforms
+    from torchvision.datasets import CIFAR10
+    from torchvision.models import resnet18
+    from tqdm import tqdm
+
+
+   +try:
+   +    _CHECKPTS_DIR = f"{os.environ['SCRATCH']}/checkpoints"
+   +except KeyError:
+   +    _CHECKPTS_DIR = "../checkpoints"
+   +
+   +
+    def main():
+        training_epochs = 10
+        learning_rate = 5e-4
+        weight_decay = 1e-4
+        batch_size = 128
+   +    resume_file = f"{_CHECKPTS_DIR}/resnet18_cifar10/checkpoint.pth.tar"
+   +    start_epoch = 0
+   +    best_acc = 0
+
+        # Check that the GPU is available
+        assert torch.cuda.is_available() and torch.cuda.device_count() > 0
+        device = torch.device("cuda", 0)
+
+        # Setup logging (optional, but much better than using print statements)
+        logging.basicConfig(
+            level=logging.INFO,
+            handlers=[rich.logging.RichHandler(markup=True)],  # Very pretty, uses the `rich` package.
+        )
+
+        logger = logging.getLogger(__name__)
+
+   -    # Create a model and move it to the GPU.
+   +    # Create a model.
+        model = resnet18(num_classes=10)
+   +
+   +    # Resume from a checkpoint
+   +    if os.path.isfile(resume_file):
+   +        logger.debug(f"=> loading checkpoint '{resume_file}'")
+   +        # Map model to be loaded to gpu.
+   +        checkpoint = torch.load(resume_file, map_location="cuda:0")
+   +        start_epoch = checkpoint["epoch"]
+   +        best_acc = checkpoint["best_acc"]
+   +        # best_acc may be from a checkpoint from a different GPU
+   +        best_acc = best_acc.to(device)
+   +        model.load_state_dict(checkpoint["state_dict"])
+   +        optimizer.load_state_dict(checkpoint["optimizer"])
+   +        logger.debug(f"=> loaded checkpoint '{resume_file}' (epoch {checkpoint['epoch']})")
+   +    else:
+   +        logger.debug(f"=> no checkpoint found at '{resume_file}'")
+   +
+   +    # Move the model to the GPU.
+        model.to(device=device)
+
+        optimizer = torch.optim.AdamW(model.parameters(), lr=learning_rate, weight_decay=weight_decay)
+
+        # Setup CIFAR10
+        num_workers = get_num_workers()
+   -    dataset_path = Path(os.environ.get("SLURM_TMPDIR", ".")) / "data"
+   -    train_dataset, valid_dataset, test_dataset = make_datasets(str(dataset_path))
+   +    try:
+   +        dataset_path = f"{os.environ['SLURM_TMPDIR']}/data"
+   +    except KeyError:
+   +        dataset_path = "../dataset"
+   +    train_dataset, valid_dataset, test_dataset = make_datasets(dataset_path)
+        train_dataloader = DataLoader(
+            train_dataset,
+            batch_size=batch_size,
+            num_workers=num_workers,
+            shuffle=True,
+        )
+        valid_dataloader = DataLoader(
+            valid_dataset,
+            batch_size=batch_size,
+            num_workers=num_workers,
+            shuffle=False,
+        )
+        test_dataloader = DataLoader(  # NOTE: Not used in this example.
+            test_dataset,
+            batch_size=batch_size,
+            num_workers=num_workers,
+            shuffle=False,
+        )
+
+        # Checkout the "checkpointing and preemption" example for more info!
+        logger.debug("Starting training from scratch.")
+
+   -    for epoch in range(training_epochs):
+   +    for epoch in range(start_epoch, training_epochs):
+            logger.debug(f"Starting epoch {epoch}/{training_epochs}")
+
+   -        # Set the model in training mode (important for e.g. BatchNorm and Dropout layers)
+   +        # Set the model in training mode (this is important for e.g. BatchNorm and Dropout layers)
+            model.train()
+
+            # NOTE: using a progress bar from tqdm because it's nicer than using `print`.
+            progress_bar = tqdm(
+                total=len(train_dataloader),
+                desc=f"Train epoch {epoch}",
+            )
+
+            # Training loop
+            for batch in train_dataloader:
+                # Move the batch to the GPU before we pass it to the model
+                batch = tuple(item.to(device) for item in batch)
+                x, y = batch
+
+                # Forward pass
+                logits: Tensor = model(x)
+
+                loss = F.cross_entropy(logits, y)
+
+                optimizer.zero_grad()
+                loss.backward()
+                optimizer.step()
+
+                # Calculate some metrics:
+                n_correct_predictions = logits.detach().argmax(-1).eq(y).sum()
+                n_samples = y.shape[0]
+                accuracy = n_correct_predictions / n_samples
+
+                logger.debug(f"Accuracy: {accuracy.item():.2%}")
+                logger.debug(f"Average Loss: {loss.item()}")
+
+                # Advance the progress bar one step, and update the "postfix" () the progress bar. (nicer than just)
+                progress_bar.update(1)
+                progress_bar.set_postfix(loss=loss.item(), accuracy=accuracy.item())
+            progress_bar.close()
+
+            val_loss, val_accuracy = validation_loop(model, valid_dataloader, device)
+            logger.info(f"Epoch {epoch}: Val loss: {val_loss:.3f} accuracy: {val_accuracy:.2%}")
+
+   +        # remember best acc and save checkpoint
+   +        is_best = val_accuracy > best_acc
+   +        best_acc = max(val_accuracy, best_acc)
+   +
+   +        save_checkpoint({
+   +            "epoch": epoch + 1,
+   +            "arch": "resnet18",
+   +            "state_dict": model.state_dict(),
+   +            "best_acc": best_acc,
+   +            "optimizer": optimizer.state_dict(),
+   +        }, is_best)
+   +
+        print("Done!")
+
+
+    @torch.no_grad()
+    def validation_loop(model: nn.Module, dataloader: DataLoader, device: torch.device):
+        model.eval()
+
+        total_loss = 0.0
+        n_samples = 0
+        correct_predictions = 0
+
+        for batch in dataloader:
+            batch = tuple(item.to(device) for item in batch)
+            x, y = batch
+
+            logits: Tensor = model(x)
+            loss = F.cross_entropy(logits, y)
+
+            batch_n_samples = x.shape[0]
+            batch_correct_predictions = logits.argmax(-1).eq(y).sum()
+
+            total_loss += loss.item()
+            n_samples += batch_n_samples
+            correct_predictions += batch_correct_predictions
+
+        accuracy = correct_predictions / n_samples
+        return total_loss, accuracy
+
+
+    def make_datasets(
+        dataset_path: str,
+        val_split: float = 0.1,
+        val_split_seed: int = 42,
+    ):
+        """Returns the training, validation, and test splits for CIFAR10.
+
+        NOTE: We don't use image transforms here for simplicity.
+        Having different transformations for train and validation would complicate things a bit.
+        Later examples will show how to do the train/val/test split properly when using transforms.
+        """
+        train_dataset = CIFAR10(
+            root=dataset_path, transform=transforms.ToTensor(), download=True, train=True
+        )
+        test_dataset = CIFAR10(
+            root=dataset_path, transform=transforms.ToTensor(), download=True, train=False
+        )
+        # Split the training dataset into a training and validation set.
+   -    n_samples = len(train_dataset)
+   -    n_valid = int(val_split * n_samples)
+   -    n_train = n_samples - n_valid
+        train_dataset, valid_dataset = random_split(
+   -        train_dataset, (n_train, n_valid), torch.Generator().manual_seed(val_split_seed)
+   +        train_dataset, ((1 - val_split), val_split), torch.Generator().manual_seed(val_split_seed)
+        )
+        return train_dataset, valid_dataset, test_dataset
+
+
+    def get_num_workers() -> int:
+        """Gets the optimal number of DatLoader workers to use in the current job."""
+        if "SLURM_CPUS_PER_TASK" in os.environ:
+            return int(os.environ["SLURM_CPUS_PER_TASK"])
+        if hasattr(os, "sched_getaffinity"):
+            return len(os.sched_getaffinity(0))
+        return torch.multiprocessing.cpu_count()
+
+
+   +def save_checkpoint(state, is_best, filename=f"{_CHECKPTS_DIR}/checkpoint.pth.tar"):
+   +    torch.save(state, filename)
+   +    if is_best:
+   +        _dir = os.path.dirname(filename)
+   +        shutil.copyfile(filename, f"{_dir}/model_best.pth.tar")
+   +
+   +
+    if __name__ == "__main__":
+        main()
+
+
+**Running this example**
+
+.. code-block:: bash
+
+   $ sbatch job.sh

docs/examples/data/checkpointing/_index.rst

@@ -0,0 +1,34 @@
+Checkpointing
+=============
+
+
+**Prerequisites**
+
+Make sure to read the following sections of the documentation before using this
+example:
+
+* :ref:`pytorch_setup`
+* :ref:`001 - Single GPU Job`
+
+The full source code for this example is available on `the mila-docs GitHub
+repository.
+<https://github.com/mila-iqia/mila-docs/tree/master/docs/examples/data/checkpointing>`_
+
+
+**job.sh**
+
+.. literalinclude:: examples/data/checkpointing/job.sh.diff
+   :language: diff
+
+
+**main.py**
+
+.. literalinclude:: examples/data/checkpointing/main.py.diff
+   :language: diff
+
+
+**Running this example**
+
+.. code-block:: bash
+
+   $ sbatch job.sh