Add comments on swap space (vllm-project#154)

Author: WoosukKwon

benchmarks/benchmark_serving.py

@@ -3,7 +3,8 @@
 On the server side, run one of the following commands:
     (vLLM backend)
     python -m vllm.entrypoints.api_server \
-        --disable-log-requests --model <your_model>
+        --model <your_model> --swap-space 16 \
+        --disable-log-requests
 
     (TGI backend)
     ./launch_hf_server.sh <your_model>

vllm/core/scheduler.py

@@ -409,7 +409,12 @@ def _swap_out(
         seq_group: SequenceGroup,
         blocks_to_swap_out: Dict[int, int],
     ) -> None:
-        assert self.block_manager.can_swap_out(seq_group)
+        if not self.block_manager.can_swap_out(seq_group):
+            # FIXME(woosuk): Abort the sequence group instead of aborting the
+            # entire engine.
+            raise RuntimeError(
+                "Aborted due to the lack of CPU swap space. Please increase "
+                "the swap space to avoid this error.")
         mapping = self.block_manager.swap_out(seq_group)
         blocks_to_swap_out.update(mapping)
         for seq in seq_group.get_seqs(status=SequenceStatus.RUNNING):