LoRA patching optimization (#6439)

* allow model patcher to optimize away the unpatching step when feasible

* remove lazy_offloading functionality

* allow model patcher to optimize away the unpatching step when feasible

* remove lazy_offloading functionality

* do not save original weights if there is a CPU copy of state dict

* Update invokeai/backend/model_manager/load/load_base.py

Co-authored-by: Ryan Dick <ryanjdick3@gmail.com>

* documentation fixes added during penultimate review

---------

Co-authored-by: Lincoln Stein <lstein@gmail.com>
Co-authored-by: Kent Keirsey <31807370+hipsterusername@users.noreply.github.com>
Co-authored-by: Ryan Dick <ryanjdick3@gmail.com>

invokeai/backend/model_manager/load/load_base.py

@@ -4,10 +4,13 @@ Base class for model loading in InvokeAI.
 """
 
 from abc import ABC, abstractmethod
+from contextlib import contextmanager
 from dataclasses import dataclass
 from logging import Logger
 from pathlib import Path
-from typing import Any, Optional
+from typing import Any, Dict, Generator, Optional, Tuple
+
+import torch
 
 from invokeai.app.services.config import InvokeAIAppConfig
 from invokeai.backend.model_manager.config import (
@@ -21,7 +24,42 @@ from invokeai.backend.model_manager.load.model_cache.model_cache_base import Mod
 
 @dataclass
 class LoadedModel:
-    """Context manager object that mediates transfer from RAM<->VRAM."""
+    """
+    Context manager object that mediates transfer from RAM<->VRAM.
+
+    This is a context manager object that has two distinct APIs:
+
+    1. Older API (deprecated):
+    Use the LoadedModel object directly as a context manager.
+    It will move the model into VRAM (on CUDA devices), and
+    return the model in a form suitable for passing to torch.
+    Example:
+    ```
+    loaded_model_= loader.get_model_by_key('f13dd932', SubModelType('vae'))
+    with loaded_model as vae:
+      image = vae.decode(latents)[0]
+    ```
+
+    2. Newer API (recommended):
+    Call the LoadedModel's `model_on_device()` method in a
+    context. It returns a tuple consisting of a copy of
+    the model's state dict in CPU RAM followed by a copy
+    of the model in VRAM. The state dict is provided to allow
+    LoRAs and other model patchers to return the model to
+    its unpatched state without expensive copy and restore
+    operations.
+
+    Example:
+    ```
+    loaded_model_= loader.get_model_by_key('f13dd932', SubModelType('vae'))
+    with loaded_model.model_on_device() as (state_dict, vae):
+        image = vae.decode(latents)[0]
+    ```
+
+    The state_dict should be treated as a read-only object and
+    never modified. Also be aware that some loadable models do
+    not have a state_dict, in which case this value will be None.
+    """
 
     config: AnyModelConfig
     _locker: ModelLockerBase
@@ -35,6 +73,16 @@ class LoadedModel:
         """Context exit."""
         self._locker.unlock()
 
+    @contextmanager
+    def model_on_device(self) -> Generator[Tuple[Optional[Dict[str, torch.Tensor]], AnyModel], None, None]:
+        """Return a tuple consisting of the model's state dict (if it exists) and the locked model on execution device."""
+        locked_model = self._locker.lock()
+        try:
+            state_dict = self._locker.get_state_dict()
+            yield (state_dict, locked_model)
+        finally:
+            self._locker.unlock()
+
     @property
     def model(self) -> AnyModel:
         """Return the model without locking it."""

invokeai/backend/model_manager/load/model_cache/model_cache_base.py

@@ -30,6 +30,11 @@ class ModelLockerBase(ABC):
         """Unlock the contained model, and remove it from VRAM."""
         pass
 
+    @abstractmethod
+    def get_state_dict(self) -> Optional[Dict[str, torch.Tensor]]:
+        """Return the state dict (if any) for the cached model."""
+        pass
+
     @property
     @abstractmethod
     def model(self) -> AnyModel:
@@ -56,6 +61,11 @@ class CacheRecord(Generic[T]):
     and then injected into the model. When the model is finished, the VRAM
     copy of the state dict is deleted, and the RAM version is reinjected
     into the model.
+
+    The state_dict should be treated as a read-only attribute. Do not attempt
+    to patch or otherwise modify it. Instead, patch the copy of the state_dict
+    after it is loaded into the execution device (e.g. CUDA) using the `LoadedModel`
+    context manager call `model_on_device()`.
     """
 
     key: str

invokeai/backend/model_manager/load/model_cache/model_locker.py

@@ -2,6 +2,8 @@
 Base class and implementation of a class that moves models in and out of VRAM.
 """
 
+from typing import Dict, Optional
+
 import torch
 
 from invokeai.backend.model_manager import AnyModel
@@ -27,6 +29,10 @@ class ModelLocker(ModelLockerBase):
         """Return the model without moving it around."""
         return self._cache_entry.model
 
+    def get_state_dict(self) -> Optional[Dict[str, torch.Tensor]]:
+        """Return the state dict (if any) for the cached model."""
+        return self._cache_entry.state_dict
+
     def lock(self) -> AnyModel:
         """Move the model into the execution device (GPU) and lock it."""
         if not hasattr(self.model, "to"):
@@ -37,10 +43,8 @@ class ModelLocker(ModelLockerBase):
         try:
             if self._cache.lazy_offloading:
                 self._cache.offload_unlocked_models(self._cache_entry.size)
-
             self._cache.move_model_to_device(self._cache_entry, self._cache.execution_device)
             self._cache_entry.loaded = True
-
             self._cache.logger.debug(f"Locking {self._cache_entry.key} in {self._cache.execution_device}")
             self._cache.print_cuda_stats()
         except torch.cuda.OutOfMemoryError: