[Core] Free CPU pinned memory on environment cleanup (vllm-project#10477)

Author: janimo

vllm/distributed/parallel_state.py

@@ -1183,6 +1183,11 @@ def cleanup_dist_env_and_memory(shutdown_ray: bool = False):
     from vllm.platforms import current_platform
     if not current_platform.is_cpu():
         torch.cuda.empty_cache()
+    try:
+        torch._C._host_emptyCache()
+    except AttributeError:
+        logger.warning(
+            "torch._C._host_emptyCache() only available in Pytorch >=2.5")
 
 
 def in_the_same_node_as(pg: Union[ProcessGroup, StatelessProcessGroup],