Add support for other normalizations in MobileNetV2 (#2267)

* Add norm_layer to MobileNetV2

* Add simple test case

* Small fix

test/test_models.py

@@ -2,6 +2,7 @@ from common_utils import TestCase, map_nested_tensor_object, freeze_rng_state
 from collections import OrderedDict
 from itertools import product
 import torch
+import torch.nn as nn
 import numpy as np
 from torchvision import models
 import unittest
@@ -240,6 +241,17 @@ class ModelTester(TestCase):
         out = model(x)
         self.assertEqual(out.shape[-1], 1000)
 
+    def test_mobilenetv2_norm_layer(self):
+        model = models.__dict__["mobilenet_v2"]()
+        self.assertTrue(any(isinstance(x, nn.BatchNorm2d) for x in model.modules()))
+
+        def get_gn(num_channels):
+            return nn.GroupNorm(32, num_channels)
+
+        model = models.__dict__["mobilenet_v2"](norm_layer=get_gn)
+        self.assertFalse(any(isinstance(x, nn.BatchNorm2d) for x in model.modules()))
+        self.assertTrue(any(isinstance(x, nn.GroupNorm) for x in model.modules()))
+
     def test_fasterrcnn_double(self):
         model = models.detection.fasterrcnn_resnet50_fpn(num_classes=50, pretrained_backbone=False)
         model.double()

torchvision/models/mobilenet.py

@@ -31,34 +31,39 @@ def _make_divisible(v, divisor, min_value=None):
 
 
 class ConvBNReLU(nn.Sequential):
-    def __init__(self, in_planes, out_planes, kernel_size=3, stride=1, groups=1):
+    def __init__(self, in_planes, out_planes, kernel_size=3, stride=1, groups=1, norm_layer=None):
         padding = (kernel_size - 1) // 2
+        if norm_layer is None:
+            norm_layer = nn.BatchNorm2d
         super(ConvBNReLU, self).__init__(
             nn.Conv2d(in_planes, out_planes, kernel_size, stride, padding, groups=groups, bias=False),
-            nn.BatchNorm2d(out_planes),
+            norm_layer(out_planes),
             nn.ReLU6(inplace=True)
         )
 
 
 class InvertedResidual(nn.Module):
-    def __init__(self, inp, oup, stride, expand_ratio):
+    def __init__(self, inp, oup, stride, expand_ratio, norm_layer=None):
         super(InvertedResidual, self).__init__()
         self.stride = stride
         assert stride in [1, 2]
 
+        if norm_layer is None:
+            norm_layer = nn.BatchNorm2d
+
         hidden_dim = int(round(inp * expand_ratio))
         self.use_res_connect = self.stride == 1 and inp == oup
 
         layers = []
         if expand_ratio != 1:
             # pw
-            layers.append(ConvBNReLU(inp, hidden_dim, kernel_size=1))
+            layers.append(ConvBNReLU(inp, hidden_dim, kernel_size=1, norm_layer=norm_layer))
         layers.extend([
             # dw
-            ConvBNReLU(hidden_dim, hidden_dim, stride=stride, groups=hidden_dim),
+            ConvBNReLU(hidden_dim, hidden_dim, stride=stride, groups=hidden_dim, norm_layer=norm_layer),
             # pw-linear
             nn.Conv2d(hidden_dim, oup, 1, 1, 0, bias=False),
-            nn.BatchNorm2d(oup),
+            norm_layer(oup),
         ])
         self.conv = nn.Sequential(*layers)
 
@@ -75,7 +80,8 @@ class MobileNetV2(nn.Module):
                  width_mult=1.0,
                  inverted_residual_setting=None,
                  round_nearest=8,
-                 block=None):
+                 block=None,
+                 norm_layer=None):
         """
         MobileNet V2 main class
 
@@ -86,12 +92,17 @@ class MobileNetV2(nn.Module):
             round_nearest (int): Round the number of channels in each layer to be a multiple of this number
             Set to 1 to turn off rounding
             block: Module specifying inverted residual building block for mobilenet
+            norm_layer: Module specifying the normalization layer to use
 
         """
         super(MobileNetV2, self).__init__()
 
         if block is None:
             block = InvertedResidual
+
+        if norm_layer is None:
+            norm_layer = nn.BatchNorm2d
+
         input_channel = 32
         last_channel = 1280
 
@@ -115,16 +126,16 @@ class MobileNetV2(nn.Module):
         # building first layer
         input_channel = _make_divisible(input_channel * width_mult, round_nearest)
         self.last_channel = _make_divisible(last_channel * max(1.0, width_mult), round_nearest)
-        features = [ConvBNReLU(3, input_channel, stride=2)]
+        features = [ConvBNReLU(3, input_channel, stride=2, norm_layer=norm_layer)]
         # building inverted residual blocks
         for t, c, n, s in inverted_residual_setting:
             output_channel = _make_divisible(c * width_mult, round_nearest)
             for i in range(n):
                 stride = s if i == 0 else 1
-                features.append(block(input_channel, output_channel, stride, expand_ratio=t))
+                features.append(block(input_channel, output_channel, stride, expand_ratio=t, norm_layer=norm_layer))
                 input_channel = output_channel
         # building last several layers
-        features.append(ConvBNReLU(input_channel, self.last_channel, kernel_size=1))
+        features.append(ConvBNReLU(input_channel, self.last_channel, kernel_size=1, norm_layer=norm_layer))
         # make it nn.Sequential
         self.features = nn.Sequential(*features)
 
@@ -140,7 +151,7 @@ class MobileNetV2(nn.Module):
                 nn.init.kaiming_normal_(m.weight, mode='fan_out')
                 if m.bias is not None:
                     nn.init.zeros_(m.bias)
-            elif isinstance(m, nn.BatchNorm2d):
+            elif isinstance(m, (nn.BatchNorm2d, nn.GroupNorm)):
                 nn.init.ones_(m.weight)
                 nn.init.zeros_(m.bias)
             elif isinstance(m, nn.Linear):