add --max-tokens-valid option for validation

Summary: Add the max-token-valid option. Sometime a separate max batch tokens for validation may be helpful, for example when there is a long sequence in validation set thats larger than max_tokens (it's rare in MT but could happen in ASR or AST).

Reviewed By: myleott

Differential Revision: D16076951

fbshipit-source-id: ae7f4218594580b9450a8196d7afa1e7e2018aee

fairseq/options.py

@@ -114,6 +114,8 @@ def parse_args_and_arch(parser, input_args=None, parse_known=False):
     # Post-process args.
     if hasattr(args, 'max_sentences_valid') and args.max_sentences_valid is None:
         args.max_sentences_valid = args.max_sentences
+    if hasattr(args, 'max_tokens_valid') and args.max_tokens_valid is None:
+        args.max_tokens_valid = args.max_tokens
     if getattr(args, 'memory_efficient_fp16', False):
         args.fp16 = True
 
@@ -252,6 +254,9 @@ def add_dataset_args(parser, train=False, gen=False):
                            help='validate every N epochs')
         group.add_argument('--disable-validation', action='store_true',
                            help='disable validation')
+        group.add_argument('--max-tokens-valid', type=int, metavar='N',
+                           help='maximum number of tokens in a validation batch'
+                                ' (defaults to --max-tokens)')
         group.add_argument('--max-sentences-valid', type=int, metavar='N',
                            help='maximum number of sentences in a validation batch'
                                 ' (defaults to --max-sentences)')

train.py

@@ -198,7 +198,7 @@ def validate(args, trainer, task, epoch_itr, subsets):
         # Initialize data iterator
         itr = task.get_batch_iterator(
             dataset=task.dataset(subset),
-            max_tokens=args.max_tokens,
+            max_tokens=args.max_tokens_valid,
             max_sentences=args.max_sentences_valid,
             max_positions=utils.resolve_max_positions(
                 task.max_positions(),