[bugfix] Resolve memory leak for evaluation

pytorch_lightning/trainer/evaluation_loop.py

@@ -203,6 +203,10 @@ def __run_eval_epoch_end(self, num_dataloaders):
 
         # with a single dataloader don't pass an array
         outputs = self.outputs
+
+        # free memory
+        self.outputs = []
+
         eval_results = outputs
         if num_dataloaders == 1:
             eval_results = outputs[0]

tests/callbacks/test_pruning.py

@@ -11,7 +11,6 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-import os
 from collections import OrderedDict
 from logging import INFO
 
@@ -22,7 +21,7 @@
 from torch.nn import Sequential
 
 from pytorch_lightning import seed_everything, Trainer
-from pytorch_lightning.callbacks import ModelPruning, ModelCheckpoint
+from pytorch_lightning.callbacks import ModelCheckpoint, ModelPruning
 from pytorch_lightning.utilities.exceptions import MisconfigurationException
 from tests.helpers import BoringModel
 from tests.helpers.runif import RunIf
@@ -274,6 +273,7 @@ def test_permanent_when_model_is_saved_multiple_times(tmpdir, caplog):
     seed_everything(0)
 
     class TestPruning(ModelPruning):
+
         def on_save_checkpoint(self, trainer, pl_module, checkpoint):
             super().on_save_checkpoint(trainer, pl_module, checkpoint)
             assert "layer.mlp_3.weight_orig" not in checkpoint["state_dict"]

tests/trainer/logging_/test_eval_loop_logging_1_0.py

@@ -126,6 +126,7 @@ def validation_step_end(self, acc):
         def validation_epoch_end(self, outputs):
             self.log('g', torch.tensor(2, device=self.device), on_epoch=True)
             self.validation_epoch_end_called = True
+            assert len(self.trainer.evaluation_loop.outputs) == 0
 
         def backward(self, loss, optimizer, optimizer_idx):
             return LightningModule.backward(self, loss, optimizer, optimizer_idx)

tests/trainer/logging_/test_logger_connector.py

@@ -478,6 +478,7 @@ def test_auto_add_dataloader_idx(tmpdir, add_dataloader_idx):
     """ test that auto_add_dataloader_idx argument works """
 
     class TestModel(BoringModel):
+
         def val_dataloader(self):
             dl = super().val_dataloader()
             return [dl, dl]
@@ -495,10 +496,7 @@ def validation_step(self, *args, **kwargs):
     model = TestModel()
     model.validation_epoch_end = None
 
-    trainer = Trainer(
-        default_root_dir=tmpdir,
-        max_steps=5
-    )
+    trainer = Trainer(default_root_dir=tmpdir, max_steps=5)
     trainer.fit(model)
     logged = trainer.logged_metrics