Allow custom activation in SqueezeExcitation of EfficientNet (#4448)

* allow custom activation in SqueezeExcitation

* use ReLU as the default activation

* make scale activation parameterizable
Co-authored-by: Vasilis Vryniotis <datumbox@users.noreply.github.com>

torchvision/models/efficientnet.py

@@ -32,17 +32,25 @@ model_urls = {
 
 
 class SqueezeExcitation(nn.Module):
-    def __init__(self, input_channels: int, squeeze_channels: int):
+    def __init__(
+        self,
+        input_channels: int,
+        squeeze_channels: int,
+        activation: Callable[..., nn.Module] = nn.ReLU,
+        scale_activation: Callable[..., nn.Module] = nn.Sigmoid,
+    ) -> None:
         super().__init__()
         self.fc1 = nn.Conv2d(input_channels, squeeze_channels, 1)
         self.fc2 = nn.Conv2d(squeeze_channels, input_channels, 1)
+        self.activation = activation()
+        self.scale_activation = scale_activation()
 
     def _scale(self, input: Tensor) -> Tensor:
         scale = F.adaptive_avg_pool2d(input, 1)
         scale = self.fc1(scale)
-        scale = F.silu(scale, inplace=True)
+        scale = self.activation(scale)
         scale = self.fc2(scale)
-        return scale.sigmoid()
+        return self.scale_activation(scale)
 
     def forward(self, input: Tensor) -> Tensor:
         scale = self._scale(input)
@@ -108,7 +116,7 @@ class MBConv(nn.Module):
 
         # squeeze and excitation
         squeeze_channels = max(1, cnf.input_channels // 4)
-        layers.append(se_layer(expanded_channels, squeeze_channels))
+        layers.append(se_layer(expanded_channels, squeeze_channels, activation=partial(nn.SiLU, inplace=True)))
 
         # project
         layers.append(ConvBNActivation(expanded_channels, cnf.out_channels, kernel_size=1, norm_layer=norm_layer,