MPS unified memory cache empty (#16078)

Co-authored-by: UltralyticsAssistant <web@ultralytics.com>
Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

ultralytics/engine/trainer.py

@@ -28,6 +28,7 @@ from ultralytics.utils import (
     DEFAULT_CFG,
     LOCAL_RANK,
     LOGGER,
+    MACOS,
     RANK,
     TQDM,
     __version__,
@@ -453,7 +454,10 @@ class BaseTrainer:
                 self.stop |= epoch >= self.epochs  # stop if exceeded epochs
             self.run_callbacks("on_fit_epoch_end")
             gc.collect()
-            torch.cuda.empty_cache()  # clear GPU memory at end of epoch, may help reduce CUDA out of memory errors
+            if MACOS:
+                torch.mps.empty_cache()  # clear unified memory at end of epoch, may help MPS' management of 'unlimited' virtual memoy
+            else:
+                torch.cuda.empty_cache()  # clear GPU memory at end of epoch, may help reduce CUDA out of memory errors
 
             # Early Stopping
             if RANK != -1:  # if DDP training
@@ -475,7 +479,11 @@ class BaseTrainer:
                 self.plot_metrics()
             self.run_callbacks("on_train_end")
         gc.collect()
-        torch.cuda.empty_cache()
+        if MACOS:
+            torch.mps.empty_cache()
+        else:
+            torch.cuda.empty_cache()
+
         self.run_callbacks("teardown")
 
     def read_results_csv(self):