feat(swap): Add shell-based block swapping for WanVideo models

This commit introduces a new block swapping mechanism specifically for WanVideo models to enable running them on GPUs with limited VRAM.

A new `WanVideoBlockSwapManager` is implemented which uses a pre-allocation or "shell" strategy. Instead of moving entire blocks between CPU and GPU, this approach:
1.  Pre-allocates a single "shell" block on the GPU, sized to match the largest block in the model.
2.  Offloads designated model blocks to the CPU.
3.  Patches the `forward` method of these offloaded blocks.
4.  During inference, the patched method copies the weights (`state_dict`) from the CPU block into the GPU shell just before execution.

This method avoids the overhead of allocating and deallocating GPU memory for each block, reducing memory fragmentation and potentially improving performance and or corruption copying potentially modified blocks back to the swap space.

block_swap.py

@@ -76,6 +76,40 @@ class QwenBlockSwapManager:
         self.patched_blocks = {}
 
 
+class WanVideoBlockSwapManager:
+    """
+    Manages block-swapping for WanVideo models using a pre-allocated GPU shell block.
+    """
+    def __init__(self, model_patcher, gpu_shell_block):
+        self.model_patcher = model_patcher
+        self.gpu_shell_block = gpu_shell_block
+        self.patched_blocks = {}
+
+    def apply_patch(self, compute_device, swap_device, blocks_to_swap):
+        logging.info(f"[WanVideoBlockSwapManager] Applying state_dict patch to {len(blocks_to_swap)} blocks.")
+        for i, block in enumerate(blocks_to_swap):
+            block.to(swap_device) # Ensure the source block is on the swap device
+            original_forward = block.forward
+            
+            def create_patched_forward(cpu_block, gpu_shell):
+                def patched_forward(*args, **kwargs):
+                    logging.info(f"[DEBUG WANVIDEO SWAP] Loading state_dict from CPU block into GPU shell.")
+                    gpu_shell.load_state_dict(cpu_block.state_dict())
+                    logging.info(f"[DEBUG WANVIDEO SWAP] Executing forward pass on GPU shell.")
+                    result = gpu_shell.forward(*args, **kwargs)
+                    return result
+                return patched_forward
+
+            block.forward = create_patched_forward(block, self.gpu_shell_block)
+            self.patched_blocks[block] = original_forward
+
+    def cleanup(self):
+        logging.info(f"[WanVideoBlockSwapManager] Cleaning up {len(self.patched_blocks)} patched blocks.")
+        for block, original_forward in self.patched_blocks.items():
+            block.forward = original_forward
+        self.patched_blocks = {}
+
+
 def analyze_safetensor_distorch(model, compute_device, swap_device, virtual_vram_gb, all_blocks, blocks_to_swap):
     """Provides a detailed analysis of the block swap configuration, mimicking the GGUF DisTorch style."""
     
@@ -253,6 +287,66 @@ def apply_block_swap(model_patcher, compute_device="cuda:0", swap_device="cpu",
 
         logging.info("[BlockSwap] QWEN block swap setup complete.")
 
+    elif model_type == "WANVIDEO":
+        model_to_patch = model_patcher.model.diffusion_model
+        
+        if not hasattr(model_to_patch, 'blocks'):
+             logging.error("[BlockSwap] CRITICAL: Could not find 'blocks' in WanVideo model. Please analyze model structure.")
+             log_unsupported_model_analysis(model_patcher)
+             return
+
+        all_blocks = model_to_patch.blocks
+
+        if not all_blocks:
+            logging.error("[BlockSwap] CRITICAL: No swappable blocks found for WanVideo model.")
+            return
+
+        # --- Pre-allocation Strategy ---
+        # 1. Find the largest block to create a shell
+        largest_block = max(all_blocks, key=lambda b: sum(p.numel() * p.element_size() for p in b.parameters()))
+        gpu_shell_block = copy.deepcopy(largest_block).to(compute_device)
+        shell_size_mb = sum(p.numel() * p.element_size() for p in gpu_shell_block.parameters()) / (1024**2)
+        logging.info(f"[BlockSwap] Created GPU shell block for WanVideo on {compute_device}, size: {shell_size_mb:.2f} MB")
+        
+        manager = WanVideoBlockSwapManager(model_patcher, gpu_shell_block)
+        # --- End Pre-allocation ---
+
+        model_size_gb = sum(p.numel() * p.element_size() for p in model_to_patch.parameters()) / (1024**3)
+
+        if virtual_vram_gb > model_size_gb:
+            logging.warning(f"[BlockSwap] virtual_vram_gb ({virtual_vram_gb:.2f} GB) is larger than the model size ({model_size_gb:.2f} GB). Truncating to model size.")
+            virtual_vram_gb = model_size_gb
+            
+        vram_target_bytes = virtual_vram_gb * (1024**3)
+        current_swap_size = 0
+        blocks_to_swap = []
+
+        # We still need to identify which blocks to swap (i.e., which ones will use the shell)
+        for block in reversed(all_blocks):
+            if current_swap_size < vram_target_bytes:
+                block_size = sum(p.numel() * p.element_size() for p in block.parameters())
+                blocks_to_swap.append(block)
+                current_swap_size += block_size
+            else:
+                # The rest of the blocks will remain on the compute device and not be patched
+                block.to(compute_device)
+
+        blocks_to_swap.reverse()
+
+        analyze_safetensor_distorch(model_to_patch, compute_device, swap_device, virtual_vram_gb, all_blocks, blocks_to_swap)
+
+        if not blocks_to_swap:
+            logging.warning("[BlockSwap] No blocks designated for swapping for WanVideo model.")
+            return
+
+        manager.apply_patch(compute_device, swap_device, blocks_to_swap)
+
+        if not hasattr(model_patcher, 'block_swap_managers'):
+            model_patcher.block_swap_managers = []
+        model_patcher.block_swap_managers.append(manager)
+
+        logging.info("[BlockSwap] WanVideo block swap setup complete using pre-allocation strategy.")
+
     else:
         logging.warning(f"[BlockSwap] Model type '{model_type}' is not yet supported. Logging model structure for analysis.")
         log_unsupported_model_analysis(model_patcher)

model_sig.py

@@ -12,6 +12,8 @@ def get_model_type(model_patcher):
             return "FLUX"
         if "Qwen" in class_name:
             return "QWEN"
+        if "WanModel" in class_name:
+            return "WANVIDEO"
             
     # Fallback to the model_type enum for other cases
     if hasattr(model_patcher, 'model') and hasattr(model_patcher.model, 'model_type'):