kohya_lora_loader.py

import math
import safetensors
import torch
from diffusers import DiffusionPipeline

"""
Kohya's LoRA format Loader for Diffusers

Usage:
```py

# An usual Diffusers' setup
import torch
from diffusers import StableDiffusionPipeline
pipe = StableDiffusionPipeline.from_pretrained('...',
                                               torch_dtype=torch.float16).to('cuda')

# Import this module
import kohya_lora_loader

# Install LoRA hook. This append apply_loar and remove_loar methods to the pipe.
kohya_lora_loader.install_lora_hook(pipe)

# Load 'lora1.safetensors' file and apply
lora1 = pipe.apply_lora('lora1.safetensors', 1.0)

# You can change alpha
lora1.alpha = 0.5

# Load 'lora2.safetensors' file and apply
lora2 = pipe.apply_lora('lora2.safetensors', 1.0)

# Generate image with lora1 and lora2 applied
pipe(...).images[0]

# Remove lora2
pipe.remove_lora(lora2)

# Generate image with lora1 applied
pipe(...).images[0]

# Uninstall LoRA hook
kohya_lora_loader.uninstall_lora_hook(pipe)

# Generate image with none LoRA applied
pipe(...).images[0]

```
"""


# modified from https://github.com/kohya-ss/sd-scripts/blob/ad5f318d066c52e5b27306b399bc87e41f2eef2b/networks/lora.py#L17
class LoRAModule(torch.nn.Module):
    def __init__(
        self, org_module: torch.nn.Module, lora_dim=4, alpha=1.0, multiplier=1.0
    ):
        """if alpha == 0 or None, alpha is rank (no scaling)."""
        super().__init__()

        if org_module.__class__.__name__ == "Conv2d":
            in_dim = org_module.in_channels
            out_dim = org_module.out_channels
        else:
            in_dim = org_module.in_features
            out_dim = org_module.out_features

        self.lora_dim = lora_dim

        if org_module.__class__.__name__ == "Conv2d":
            kernel_size = org_module.kernel_size
            stride = org_module.stride
            padding = org_module.padding
            self.lora_down = torch.nn.Conv2d(
                in_dim, self.lora_dim, kernel_size, stride, padding, bias=False
            )
            self.lora_up = torch.nn.Conv2d(
                self.lora_dim, out_dim, (1, 1), (1, 1), bias=False
            )
        else:
            self.lora_down = torch.nn.Linear(in_dim, self.lora_dim, bias=False)
            self.lora_up = torch.nn.Linear(self.lora_dim, out_dim, bias=False)

        if alpha is None or alpha == 0:
            self.alpha = self.lora_dim
        else:
            if type(alpha) == torch.Tensor:
                alpha = alpha.detach().float().numpy()  # without casting, bf16 causes error
            self.register_buffer("alpha", torch.tensor(alpha))  # Treatable as a constant.

        # same as microsoft's
        torch.nn.init.kaiming_uniform_(self.lora_down.weight, a=math.sqrt(5))
        torch.nn.init.zeros_(self.lora_up.weight)

        self.multiplier = multiplier

    def forward(self, x):
        scale = self.alpha / self.lora_dim
        return self.multiplier * scale * self.lora_up(self.lora_down(x))


class LoRAModuleContainer(torch.nn.Module):
    def __init__(self, hooks, state_dict, multiplier):
        super().__init__()
        self.multiplier = multiplier

        # Create LoRAModule from state_dict information
        for key, value in state_dict.items():
            if "lora_down" in key:
                lora_name = key.split(".")[0]
                lora_dim = value.size()[0]
                lora_name_alpha = key.split(".")[0] + '.alpha'
                alpha = None
                if lora_name_alpha in state_dict:
                    alpha = state_dict[lora_name_alpha].item()
                hook = hooks[lora_name]
                lora_module = LoRAModule(
                    hook.orig_module, lora_dim=lora_dim, alpha=alpha, multiplier=multiplier
                )
                self.register_module(lora_name, lora_module)

        # Load whole LoRA weights
        self.load_state_dict(state_dict)

        # Register LoRAModule to LoRAHook
        for name, module in self.named_modules():
            if module.__class__.__name__ == "LoRAModule":
                hook = hooks[name]
                hook.append_lora(module)
    @property
    def alpha(self):
        return self.multiplier

    @alpha.setter
    def alpha(self, multiplier):
        self.multiplier = multiplier
        for name, module in self.named_modules():
            if module.__class__.__name__ == "LoRAModule":
                module.multiplier = multiplier

    def remove_from_hooks(self, hooks):
        for name, module in self.named_modules():
            if module.__class__.__name__ == "LoRAModule":
                hook = hooks[name]
                hook.remove_lora(module)
                del module


class LoRAHook(torch.nn.Module):
    """
    replaces forward method of the original Linear,
    instead of replacing the original Linear module.
    """

    def __init__(self):
        super().__init__()
        self.lora_modules = []

    def install(self, orig_module):
        assert not hasattr(self, "orig_module")
        self.orig_module = orig_module
        self.orig_forward = self.orig_module.forward
        self.orig_module.forward = self.forward

    def uninstall(self):
        assert hasattr(self, "orig_module")
        self.orig_module.forward = self.orig_forward
        del self.orig_forward
        del self.orig_module

    def append_lora(self, lora_module):
        self.lora_modules.append(lora_module)

    def remove_lora(self, lora_module):
        self.lora_modules.remove(lora_module)

    def forward(self, x):
        if len(self.lora_modules) == 0:
            return self.orig_forward(x)
        lora = torch.sum(torch.stack([lora(x) for lora in self.lora_modules]), dim=0)
        return self.orig_forward(x) + lora


class LoRAHookInjector(object):
    def __init__(self):
        super().__init__()
        self.hooks = {}
        self.device = None
        self.dtype = None

    def _get_target_modules(self, root_module, prefix, target_replace_modules):
        target_modules = []
        for name, module in root_module.named_modules():
            if (
                module.__class__.__name__ in target_replace_modules
                and not "transformer_blocks" in name
            ):  # to adapt latest diffusers:
                for child_name, child_module in module.named_modules():
                    is_linear = child_module.__class__.__name__ == "Linear"
                    is_conv2d = child_module.__class__.__name__ == "Conv2d"
                    if is_linear or is_conv2d:
                        lora_name = prefix + "." + name + "." + child_name
                        lora_name = lora_name.replace(".", "_")
                        target_modules.append((lora_name, child_module))
        return target_modules

    def install_hooks(self, pipe):
        """Install LoRAHook to the pipe."""
        assert len(self.hooks) == 0
        text_encoder_targets = self._get_target_modules(
            pipe.text_encoder, "lora_te", ["CLIPAttention", "CLIPMLP"]
        )
        unet_targets = self._get_target_modules(
            pipe.unet, "lora_unet", ["Transformer2DModel", "Attention"]
        )
        for name, target_module in text_encoder_targets + unet_targets:
            hook = LoRAHook()
            hook.install(target_module)
            self.hooks[name] = hook

        self.device = pipe.device
        self.dtype = pipe.unet.dtype

    def uninstall_hooks(self):
        """Uninstall LoRAHook from the pipe."""
        for k, v in self.hooks.items():
            v.uninstall()
        self.hooks = {}

    def apply_lora(self, filename, alpha=1.0):
        """Load LoRA weights and apply LoRA to the pipe."""
        assert len(self.hooks) != 0
        state_dict = safetensors.torch.load_file(filename)
        container = LoRAModuleContainer(self.hooks, state_dict, alpha)
        container.to(self.device, self.dtype)
        return container

    def remove_lora(self, container):
        """Remove the individual LoRA from the pipe."""
        container.remove_from_hooks(self.hooks)


def install_lora_hook(pipe: DiffusionPipeline):
    """Install LoRAHook to the pipe."""
    assert not hasattr(pipe, "lora_injector")
    assert not hasattr(pipe, "apply_lora")
    assert not hasattr(pipe, "remove_lora")
    injector = LoRAHookInjector()
    injector.install_hooks(pipe)
    pipe.lora_injector = injector
    pipe.apply_lora = injector.apply_lora
    pipe.remove_lora = injector.remove_lora


def uninstall_lora_hook(pipe: DiffusionPipeline):
    """Uninstall LoRAHook from the pipe."""
    pipe.lora_injector.uninstall_hooks()
    del pipe.lora_injector
    del pipe.apply_lora
    del pipe.remove_lora

For diffusers after #4147, consider adding the following module checkings if you still want to use this hook:
at line 197

for child_name, child_module in module.named_modules():
    is_linear = child_module.__class__.__name__ in ["Linear", "LoRACompatibleLinear"]
    is_conv2d = child_module.__class__.__name__ in ["Conv2d", "LoRACompatibleConv"]

and at line 60 & 69:

if org_module.__class__.__name__ in ["Conv2d", "LoRACompatibleConv"]:

also, add a default scale in LoRAHook.forward at line 176:

def forward(self, x, scale=1.0):