simplify configure_optimizers by a lot

Author: karpathy

model.py

@@ -268,60 +268,28 @@ def from_pretrained(cls, model_type, override_args=None):
         return model
 
     def configure_optimizers(self, weight_decay, learning_rate, betas, device_type):
-        """
-        This long function is unfortunately doing something very simple and is being very defensive:
-        We are separating out all parameters of the model into two buckets: those that will experience
-        weight decay for regularization and those that won't (biases, and layernorm/embedding weights).
-        We are then returning the PyTorch optimizer object.
-        """
-
-        # separate out all parameters to those that will and won't experience regularizing weight decay
-        decay = set()
-        no_decay = set()
-        whitelist_weight_modules = (torch.nn.Linear, )
-        blacklist_weight_modules = (torch.nn.LayerNorm, LayerNorm, torch.nn.Embedding)
-        for mn, m in self.named_modules():
-            for pn, p in m.named_parameters():
-                fpn = '%s.%s' % (mn, pn) if mn else pn # full param name
-                # random note: because named_modules and named_parameters are recursive
-                # we will see the same tensors p many many times. but doing it this way
-                # allows us to know which parent module any tensor p belongs to...
-                if pn.endswith('bias'):
-                    # all biases will not be decayed
-                    no_decay.add(fpn)
-                elif pn.endswith('weight') and isinstance(m, whitelist_weight_modules):
-                    # weights of whitelist modules will be weight decayed
-                    decay.add(fpn)
-                elif pn.endswith('weight') and isinstance(m, blacklist_weight_modules):
-                    # weights of blacklist modules will NOT be weight decayed
-                    no_decay.add(fpn)
-
-        # subtle: 'transformer.wte.weight' and 'lm_head.weight' are tied, so they
-        # will appear in the no_decay and decay sets respectively after the above.
-        # In addition, because named_parameters() doesn't return duplicates, it
-        # will only return the first occurence, key'd by 'transformer.wte.weight', below.
-        # so let's manually remove 'lm_head.weight' from decay set. This will include
-        # this tensor into optimization via transformer.wte.weight only, and not decayed.
-        decay.remove('lm_head.weight')
-
-        # validate that we considered every parameter
+        # start with all of the candidate parameters
         param_dict = {pn: p for pn, p in self.named_parameters()}
-        inter_params = decay & no_decay
-        union_params = decay | no_decay
-        assert len(inter_params) == 0, "parameters %s made it into both decay/no_decay sets!" % (str(inter_params), )
-        assert len(param_dict.keys() - union_params) == 0, "parameters %s were not separated into either decay/no_decay set!" \
-                                                    % (str(param_dict.keys() - union_params), )
-
-        # create the pytorch optimizer object
+        # filter out those that do not require grad
+        param_dict = {pn: p for pn, p in param_dict.items() if p.requires_grad}
+        # create optim groups. Any parameters that is 2D will be weight decayed, otherwise no.
+        # i.e. all weight tensors in matmuls + embeddings decay, all biases and layernorms don't.
+        decay_params = [p for n, p in param_dict.items() if p.dim() >= 2]
+        nodecay_params = [p for n, p in param_dict.items() if p.dim() < 2]
         optim_groups = [
-            {"params": [param_dict[pn] for pn in sorted(list(decay))], "weight_decay": weight_decay},
-            {"params": [param_dict[pn] for pn in sorted(list(no_decay))], "weight_decay": 0.0},
+            {'params': decay_params, 'weight_decay': weight_decay},
+            {'params': nodecay_params, 'weight_decay': 0.0}
         ]
-        # new PyTorch nightly has a new 'fused' option for AdamW that is much faster
-        use_fused = (device_type == 'cuda') and ('fused' in inspect.signature(torch.optim.AdamW).parameters)
-        print(f"using fused AdamW: {use_fused}")
+        num_decay_params = sum(p.numel() for p in decay_params)
+        num_nodecay_params = sum(p.numel() for p in nodecay_params)
+        print(f"num decayed parameter tensors: {len(decay_params)}, with {num_decay_params:,} parameters")
+        print(f"num non-decayed parameter tensors: {len(nodecay_params)}, with {num_nodecay_params:,} parameters")
+        # Create AdamW optimizer and use the fused version if it is available
+        fused_available = 'fused' in inspect.signature(torch.optim.AdamW).parameters
+        use_fused = fused_available and device_type == 'cuda'
         extra_args = dict(fused=True) if use_fused else dict()
         optimizer = torch.optim.AdamW(optim_groups, lr=learning_rate, betas=betas, **extra_args)
+        print(f"using fused AdamW: {use_fused}")
 
         return optimizer