Fix VRAM leak in overlap scheduling with structured output (#20640) (#20697)

python/sglang/srt/managers/scheduler.py

@@ -2634,6 +2634,16 @@ class Scheduler(
             self.future_map.store_to_map(batch_result.future_indices, batch_result)
             batch_result.copy_to_cpu(return_logprob=self.cur_batch.return_logprob)
 
+        # Release the closure and large GPU tensors that are no longer needed.
+        # The delay_sample_func closure captures forward_batch (which holds
+        # sampling_info with vocab_mask) and logits_output (which holds
+        # next_token_logits). Without clearing these, they stay alive via
+        # batch_result in result_queue and batch_record_buf until the next
+        # iteration, causing a steady VRAM leak with structured output.
+        batch_result.delay_sample_func = None
+        if batch_result.logits_output is not None:
+            batch_result.logits_output.next_token_logits = None
+
     def process_batch_result(
         self,
         batch: ScheduleBatch,

python/sglang/srt/model_executor/model_runner.py

@@ -2727,6 +2727,13 @@ class ModelRunner(ModelRunnerKVCacheMixin):
         sampling_info.update_regex_vocab_mask()
         sampling_info.apply_logits_bias(logits_output.next_token_logits)
 
+        # Release the vocab_mask GPU tensor immediately after it has been applied
+        # to the logits. In overlap scheduling, the sampling_info (and its
+        # vocab_mask) can be kept alive by the delay_sample_func closure and
+        # batch_record_buf until the next iteration, causing a steady VRAM leak
+        # when structured output (grammar) is used.
+        sampling_info.vocab_mask = None
+
     def sample(
         self,
         logits_output: LogitsProcessorOutput,