[rllib] Replace ray.get() with ray_get_and_free() to optimize memory usage (#4586)

python/ray/rllib/optimizers/sync_replay_optimizer.py

@@ -17,6 +17,7 @@ from ray.rllib.utils.annotations import override
 from ray.rllib.utils.compression import pack_if_needed
 from ray.rllib.utils.timer import TimerStat
 from ray.rllib.utils.schedules import LinearSchedule
+from ray.rllib.utils.memory import ray_get_and_free
 
 logger = logging.getLogger(__name__)
 
@@ -89,7 +90,7 @@ class SyncReplayOptimizer(PolicyOptimizer):
         with self.sample_timer:
             if self.remote_evaluators:
                 batch = SampleBatch.concat_samples(
-                    ray.get(
+                    ray_get_and_free(
                         [e.sample.remote() for e in self.remote_evaluators]))
             else:
                 batch = self.local_evaluator.sample()