Memory check before inference to avoid VAE Decode using exceeded VRAM.

Check if free memory is not less than expected before doing actual decoding,
and if it fails, switch to tiled VAE decoding directly.

It seems PyTorch may continue occupying memory until the model is destroyed
after OOM occurs. This commit tries to avoid OOM from happening in the first
place for VAE Decode.

This is for VAE Decode ran with exceeded VRAM from #5737.

comfy/sd.py

@@ -348,11 +348,19 @@ def encode_tiled_1d(self, samples, tile_x=128 * 2048, overlap=32 * 2048):
         return comfy.utils.tiled_scale_multidim(samples, encode_fn, tile=(tile_x,), overlap=overlap, upscale_amount=(1/self.downscale_ratio), out_channels=self.latent_channels, output_device=self.output_device)
 
     def decode(self, samples_in):
+        predicted_oom = False
+        samples = None
+        out = None
         pixel_samples = None
         try:
             memory_used = self.memory_used_decode(samples_in.shape, self.vae_dtype)
             model_management.load_models_gpu([self.patcher], memory_required=memory_used)
             free_memory = model_management.get_free_memory(self.device)
+            logging.debug(f"Free memory: {free_memory} bytes, predicted memory useage of one batch: {memory_used} bytes")
+            if free_memory < memory_used:
+                logging.warning("Warning: Out of memory is predicted for regular VAE decoding, directly switch to tiled VAE decoding.")
+                predicted_oom = True
+                raise model_management.OOM_EXCEPTION
             batch_number = int(free_memory / memory_used)
             batch_number = max(1, batch_number)
 
@@ -363,7 +371,11 @@ def decode(self, samples_in):
                     pixel_samples = torch.empty((samples_in.shape[0],) + tuple(out.shape[1:]), device=self.output_device)
                 pixel_samples[x:x+batch_number] = out
         except model_management.OOM_EXCEPTION as e:
-            logging.warning("Warning: Ran out of memory when regular VAE decoding, retrying with tiled VAE decoding.")
+            samples = None
+            out = None
+            pixel_samples = None
+            if not predicted_oom:
+                logging.warning("Warning: Ran out of memory when regular VAE decoding, retrying with tiled VAE decoding.")
             dims = samples_in.ndim - 2
             if dims == 1:
                 pixel_samples = self.decode_tiled_1d(samples_in)