Fix PyTorch RAG tests GPU OOM (#16881)

* add torch.cuda.empty_cache in some PT RAG tests

* torch.cuda.empty_cache in tearDownModule()

* tearDown()

* add gc.collect()
Co-authored-by: ydshieh <ydshieh@users.noreply.github.com>

tests/rag/test_modeling_rag.py

@@ -14,6 +14,7 @@
 # limitations under the License.
 
 
+import gc
 import json
 import os
 import shutil
@@ -195,6 +196,10 @@ class RagTestMixin:
     def tearDown(self):
         shutil.rmtree(self.tmpdirname)
 
+        # clean-up as much as possible GPU memory occupied by PyTorch
+        gc.collect()
+        torch.cuda.empty_cache()
+
     def get_retriever(self, config):
         dataset = Dataset.from_dict(
             {
@@ -677,6 +682,12 @@ class RagDPRT5Test(RagTestMixin, unittest.TestCase):
 @require_tokenizers
 @require_torch_non_multi_gpu
 class RagModelIntegrationTests(unittest.TestCase):
+    def tearDown(self):
+        super().tearDown()
+        # clean-up as much as possible GPU memory occupied by PyTorch
+        gc.collect()
+        torch.cuda.empty_cache()
+
     @cached_property
     def sequence_model(self):
         return (
@@ -1024,6 +1035,12 @@ class RagModelIntegrationTests(unittest.TestCase):
 @require_torch
 @require_retrieval
 class RagModelSaveLoadTests(unittest.TestCase):
+    def tearDown(self):
+        super().tearDown()
+        # clean-up as much as possible GPU memory occupied by PyTorch
+        gc.collect()
+        torch.cuda.empty_cache()
+
     def get_rag_config(self):
         question_encoder_config = AutoConfig.from_pretrained("facebook/dpr-question_encoder-single-nq-base")
         generator_config = AutoConfig.from_pretrained("facebook/bart-large-cnn")