Support custom weight decay for Normalization layers.

references/classification/train.py

@@ -197,16 +197,22 @@ def main(args):
 
     criterion = nn.CrossEntropyLoss(label_smoothing=args.label_smoothing)
 
+    if args.norm_weight_decay is None:
+        parameters = model.parameters()
+    else:
+        param_groups = torchvision.ops._utils.split_normalization_params(model)
+        wd_groups = [args.norm_weight_decay, args.weight_decay]
+        parameters = [{"params": p, "weight_decay": w} for p, w in zip(param_groups, wd_groups) if p]
+
     opt_name = args.opt.lower()
     if opt_name.startswith("sgd"):
-        optimizer = torch.optim.SGD(
-            model.parameters(), lr=args.lr, momentum=args.momentum, weight_decay=args.weight_decay,
-            nesterov="nesterov" in opt_name)
+        optimizer = torch.optim.SGD(parameters, lr=args.lr, momentum=args.momentum, weight_decay=args.weight_decay,
+                                    nesterov="nesterov" in opt_name)
     elif opt_name == 'rmsprop':
-        optimizer = torch.optim.RMSprop(model.parameters(), lr=args.lr, momentum=args.momentum,
-                                        weight_decay=args.weight_decay, eps=0.0316, alpha=0.9)
+        optimizer = torch.optim.RMSprop(parameters, lr=args.lr, momentum=args.momentum, weight_decay=args.weight_decay,
+                                        eps=0.0316, alpha=0.9)
     elif opt_name == 'adamw':
-        optimizer = torch.optim.AdamW(model.parameters(), lr=args.lr, weight_decay=args.weight_decay)
+        optimizer = torch.optim.AdamW(parameters, lr=args.lr, weight_decay=args.weight_decay)
     else:
         raise RuntimeError(f"Invalid optimizer {args.opt}. Only SGD, RMSprop and AdamW are supported.")
 
@@ -326,6 +332,8 @@ def get_args_parser(add_help=True):
     parser.add_argument('--wd', '--weight-decay', default=1e-4, type=float,
                         metavar='W', help='weight decay (default: 1e-4)',
                         dest='weight_decay')
+    parser.add_argument('--norm-weight-decay', default=None, type=float,
+                        help='weight decay for Normalization layers (default: None, same value as --wd)')
     parser.add_argument('--label-smoothing', default=0.0, type=float,
                         help='label smoothing (default: 0.0)',
                         dest='label_smoothing')

test/test_ops.py

@@ -9,10 +9,10 @@
 from PIL import Image
 import torch
 from functools import lru_cache
-from torch import Tensor
+from torch import nn, Tensor
 from torch.autograd import gradcheck
 from torch.nn.modules.utils import _pair
-from torchvision import ops
+from torchvision import models, ops
 from typing import Tuple
 
 
@@ -1062,5 +1062,15 @@ def test_stochastic_depth(self, mode, p):
         assert p_value > 0.0001
 
 
+class TestUtils:
+    @pytest.mark.parametrize('norm_layer', [None, nn.BatchNorm2d, nn.LayerNorm])
+    def test_split_normalization_params(self, norm_layer):
+        model = models.mobilenet_v3_large(norm_layer=norm_layer)
+        params = ops._utils.split_normalization_params(model, None if norm_layer is None else [norm_layer])
+
+        assert len(params[0]) == 92
+        assert len(params[1]) == 82
+
+
 if __name__ == '__main__':
     pytest.main([__file__])

torchvision/ops/_utils.py

@@ -1,6 +1,6 @@
 import torch
-from torch import Tensor
-from typing import List, Union
+from torch import nn, Tensor
+from typing import List, Optional, Tuple, Union
 
 
 def _cat(tensors: List[Tensor], dim: int = 0) -> Tensor:
@@ -34,3 +34,27 @@ def check_roi_boxes_shape(boxes: Union[Tensor, List[Tensor]]):
     else:
         assert False, 'boxes is expected to be a Tensor[L, 5] or a List[Tensor[K, 4]]'
     return
+
+
+def split_normalization_params(model: nn.Module,
+                               norm_classes: Optional[List[type]] = None) -> Tuple[List[Tensor], List[Tensor]]:
+    # Adapted from https://github.com/facebookresearch/ClassyVision/blob/659d7f78/classy_vision/generic/util.py#L501
+    if not norm_classes:
+        norm_classes = [nn.modules.batchnorm._BatchNorm, nn.LayerNorm, nn.GroupNorm]
+
+    for t in norm_classes:
+        if not issubclass(t, nn.Module):
+            raise ValueError(f"Class {t} is not a subclass of nn.Module.")
+
+    classes = tuple(norm_classes)
+
+    norm_params = []
+    other_params = []
+    for module in model.modules():
+        if next(module.children(), None):
+            other_params.extend(p for p in module.parameters(recurse=False) if p.requires_grad)
+        elif isinstance(module, classes):
+            norm_params.extend(p for p in module.parameters() if p.requires_grad)
+        else:
+            other_params.extend(p for p in module.parameters() if p.requires_grad)
+    return norm_params, other_params