Use pytorch smooth_l1_loss and remove private custom implem (#3539)

torchvision/models/detection/_utils.py

@@ -344,19 +344,6 @@ class Matcher(object):
         matches[pred_inds_to_update] = all_matches[pred_inds_to_update]
 
 
-def smooth_l1_loss(input, target, beta: float = 1. / 9, size_average: bool = True):
-    """
-    very similar to the smooth_l1_loss from pytorch, but with
-    the extra beta parameter
-    """
-    n = torch.abs(input - target)
-    cond = n < beta
-    loss = torch.where(cond, 0.5 * n ** 2 / beta, n - 0.5 * beta)
-    if size_average:
-        return loss.mean()
-    return loss.sum()
-
-
 def overwrite_eps(model, eps):
     """
     This method overwrites the default eps values of all the

torchvision/models/detection/roi_heads.py

@@ -42,11 +42,11 @@ def fastrcnn_loss(class_logits, box_regression, labels, regression_targets):
     N, num_classes = class_logits.shape
     box_regression = box_regression.reshape(N, box_regression.size(-1) // 4, 4)
 
-    box_loss = det_utils.smooth_l1_loss(
+    box_loss = F.smooth_l1_loss(
         box_regression[sampled_pos_inds_subset, labels_pos],
         regression_targets[sampled_pos_inds_subset],
         beta=1 / 9,
-        size_average=False,
+        reduction='sum',
     )
     box_loss = box_loss / labels.numel()
 

torchvision/models/detection/rpn.py

@@ -304,11 +304,11 @@ class RegionProposalNetwork(torch.nn.Module):
         labels = torch.cat(labels, dim=0)
         regression_targets = torch.cat(regression_targets, dim=0)
 
-        box_loss = det_utils.smooth_l1_loss(
+        box_loss = F.smooth_l1_loss(
             pred_bbox_deltas[sampled_pos_inds],
             regression_targets[sampled_pos_inds],
             beta=1 / 9,
-            size_average=False,
+            reduction='sum',
         ) / (sampled_inds.numel())
 
         objectness_loss = F.binary_cross_entropy_with_logits(