Add MemoryFormat callback (channels last)

src/lightning/pytorch/CHANGELOG.md

@@ -10,6 +10,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 ### Added
 
+- Added `MemoryFormat` callback to easily change the model memory format ([#15175](https://github.com/Lightning-AI/lightning/pull/17680))
+
+
 - Added `WeightAveraging` callback that wraps the PyTorch `AveragedModel` class ([#20545](https://github.com/Lightning-AI/pytorch-lightning/pull/20545))
 
 

src/lightning/pytorch/callbacks/__init__.py

@@ -21,6 +21,7 @@
 from lightning.pytorch.callbacks.lambda_function import LambdaCallback
 from lightning.pytorch.callbacks.lr_finder import LearningRateFinder
 from lightning.pytorch.callbacks.lr_monitor import LearningRateMonitor
+from lightning.pytorch.callbacks.memory_format import MemoryFormat
 from lightning.pytorch.callbacks.model_checkpoint import ModelCheckpoint
 from lightning.pytorch.callbacks.model_summary import ModelSummary
 from lightning.pytorch.callbacks.on_exception_checkpoint import OnExceptionCheckpoint
@@ -47,6 +48,7 @@
     "LambdaCallback",
     "LearningRateFinder",
     "LearningRateMonitor",
+    "MemoryFormat",
     "ModelCheckpoint",
     "ModelPruning",
     "ModelSummary",

src/lightning/pytorch/callbacks/memory_format.py

@@ -0,0 +1,80 @@
+# Copyright The Lightning AI team.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+r"""
+MemoryFormat
+===============
+
+changes the model memory format
+"""
+
+from collections.abc import MutableSequence
+from typing import Any, Optional
+
+import torch
+
+import lightning.pytorch as pl
+from lightning.pytorch.callbacks import Callback
+from lightning.pytorch.utilities.rank_zero import rank_zero_warn
+
+
+class MemoryFormat(Callback):
+    """The `MemoryFormat` callback changes the model memory format to `torch.channels_last` before training starts and
+    returns the original when it ends.
+
+    <https://\\pytorch.org/tutorials/intermediate/memory_format_tutorial.html>`_.
+
+    Setting the memory format channels_last usually improves GPU utilization.
+
+    Runs on setup, so it can set the memory format before the model is DDP wrapped.
+
+    """
+
+    def __init__(self, memory_format: torch.memory_format = torch.channels_last, convert_input: bool = False):
+        self.memory_format = memory_format
+        self.convert_input = convert_input
+
+    def setup(self, trainer: "pl.Trainer", pl_module: "pl.LightningModule", stage: Optional[str] = None) -> None:
+        if self.memory_format in (
+            torch.channels_last,
+            torch.channels_last_3d,
+        ) and not self.has_layer_benefiting_from_channels_last(pl_module):
+            rank_zero_warn(
+                f"model does not have any layers benefiting from {self.memory_format} format", category=RuntimeWarning
+            )
+
+        pl_module.to(memory_format=self.memory_format)
+
+    def teardown(self, trainer: "pl.Trainer", pl_module: "pl.LightningModule", stage: Optional[str] = None) -> None:
+        pl_module.to(memory_format=torch.contiguous_format)
+
+    def on_train_batch_start(
+        self, trainer: "pl.Trainer", pl_module: "pl.LightningModule", batch: Any, batch_idx: int
+    ) -> None:
+        if not self.convert_input:
+            return
+
+        if not isinstance(batch, MutableSequence):
+            rank_zero_warn(
+                f"batch is not a MutableSequence, cannot convert input to {self.memory_format}", category=RuntimeWarning
+            )
+            return
+
+        for i, item in enumerate(batch):
+            if isinstance(item, torch.Tensor):
+                batch[i] = item.to(memory_format=self.memory_format)
+
+    benefitial_layers = (torch.nn.BatchNorm2d, torch.nn.BatchNorm3d, torch.nn.Conv2d, torch.nn.Conv3d)
+
+    def has_layer_benefiting_from_channels_last(self, model: torch.nn.Module) -> bool:
+        return any(isinstance(layer, self.benefitial_layers) for layer in model.modules())

tests/tests_pytorch/callbacks/test_memory_format.py

@@ -0,0 +1,76 @@
+# Copyright The Lightning AI team.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+import warnings
+from unittest.mock import MagicMock
+
+import torch
+
+from lightning.pytorch import LightningModule, Trainer
+from lightning.pytorch.callbacks import MemoryFormat
+
+
+def test_memory_format_callback_setup():
+    class DummyModule(LightningModule):
+        def __init__(self):
+            super().__init__()
+            self.conv = torch.nn.Conv2d(3, 3, kernel_size=3)
+
+        def forward(self, x):
+            return self.conv(x)
+
+    model = DummyModule()
+
+    # create a dummy Trainer
+    trainer = Trainer(max_epochs=1, devices=1)
+
+    # create the callback
+    callback = MemoryFormat()
+
+    # call the setup method
+    callback.setup(trainer, model)
+
+    # check that the memory format is channels_last
+    assert model.conv.weight.is_contiguous(memory_format=torch.channels_last)
+
+
+def test_memory_format_callback():
+    # create a mock LightningModule
+    trainer = MagicMock()
+    pl_module = MagicMock()
+
+    # create a MemoryFormat callback
+    memory_format_callback = MemoryFormat()
+
+    # check that the callback sets the memory format correctly
+    memory_format_callback.setup(trainer=trainer, pl_module=pl_module)
+    assert pl_module.to.call_args[1]["memory_format"] == torch.channels_last
+
+    # check that the callback resets the memory format correctly
+    memory_format_callback.teardown(trainer=trainer, pl_module=pl_module)
+    assert pl_module.to.call_args[1]["memory_format"] == torch.contiguous_format
+
+    # check that the callback warns if the model doesn't have any layers benefiting from channels_last
+    pl_module.modules.return_value = [torch.nn.Linear(10, 10)]
+    with warnings.catch_warnings(record=True) as w:
+        memory_format_callback.setup(trainer=trainer, pl_module=pl_module)
+        assert len(w) == 1
+        assert issubclass(w[-1].category, RuntimeWarning)
+        assert "model does not have any layers benefiting from" in str(w[-1].message)
+
+    # check that the callback converts input tensors to channels_last format
+    memory_format_callback.convert_input = True
+    batch = [torch.randn(16, 3, 32, 32), torch.randn(16, 3, 32, 32)]
+    memory_format_callback.on_train_batch_start(trainer=trainer, pl_module=pl_module, batch=batch, batch_idx=0)
+    for item in batch:
+        assert item.is_contiguous(memory_format=torch.channels_last)