[Guide] Quantize your Diffusion Models with `bnb` (#10012)

* chore: initial draft

* Apply suggestions from code review
Co-authored-by: Pedro Cuenca <pedro@huggingface.co>
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* chore: link in place

* chore: review suggestions

* Apply suggestions from code review
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* chore: review suggestions

* Update docs/source/en/quantization/bitsandbytes.md
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* review suggestions

* chore: review suggestions

* Apply suggestions from code review
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* adding same changes to 4 bit section

* review suggestions

---------
Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>
Co-authored-by: Pedro Cuenca <pedro@huggingface.co>
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

docs/source/en/quantization/bitsandbytes.md

@@ -17,6 +17,12 @@ specific language governing permissions and limitations under the License.
 
 4-bit quantization compresses a model even further, and it is commonly used with [QLoRA](https://hf.co/papers/2305.14314) to finetune quantized LLMs.
 
+This guide demonstrates how quantization can enable running
+[FLUX.1-dev](https://huggingface.co/black-forest-labs/FLUX.1-dev)
+on less than 16GB of VRAM and even on a free Google
+Colab instance.
+
+![comparison image](https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/diffusers/quant-bnb/comparison.png)
 
 To use bitsandbytes, make sure you have the following libraries installed:
 
@@ -31,70 +37,167 @@ Now you can quantize a model by passing a [`BitsAndBytesConfig`] to [`~ModelMixi
 
 Quantizing a model in 8-bit halves the memory-usage:
 
+bitsandbytes is supported in both Transformers and Diffusers, so you can quantize both the
+[`FluxTransformer2DModel`] and [`~transformers.T5EncoderModel`].
+
+For Ada and higher-series GPUs. we recommend changing `torch_dtype` to `torch.bfloat16`.
+
+> [!TIP]
+> The [`CLIPTextModel`] and [`AutoencoderKL`] aren't quantized because they're already small in size and because [`AutoencoderKL`] only has a few `torch.nn.Linear` layers.
+
 ```py
-from diffusers import FluxTransformer2DModel, BitsAndBytesConfig
+from diffusers import BitsAndBytesConfig as DiffusersBitsAndBytesConfig
+from transformers import BitsAndBytesConfig as TransformersBitsAndBytesConfig
 
-quantization_config = BitsAndBytesConfig(load_in_8bit=True)
+from diffusers import FluxTransformer2DModel
+from transformers import T5EncoderModel
 
-model_8bit = FluxTransformer2DModel.from_pretrained(
+quant_config = TransformersBitsAndBytesConfig(load_in_8bit=True,)
+
+text_encoder_2_8bit = T5EncoderModel.from_pretrained(
+    "black-forest-labs/FLUX.1-dev",
+    subfolder="text_encoder_2",
+    quantization_config=quant_config,
+    torch_dtype=torch.float16,
+)
+
+quant_config = DiffusersBitsAndBytesConfig(load_in_8bit=True,)
+
+transformer_8bit = FluxTransformer2DModel.from_pretrained(
     "black-forest-labs/FLUX.1-dev",
     subfolder="transformer",
-    quantization_config=quantization_config
+    quantization_config=quant_config,
+    torch_dtype=torch.float16,
 )
 ```
 
-By default, all the other modules such as `torch.nn.LayerNorm` are converted to `torch.float16`. You can change the data type of these modules with the `torch_dtype` parameter if you want:
+By default, all the other modules such as `torch.nn.LayerNorm` are converted to `torch.float16`. You can change the data type of these modules with the `torch_dtype` parameter.
 
-```py
-from diffusers import FluxTransformer2DModel, BitsAndBytesConfig
+```diff
+transformer_8bit = FluxTransformer2DModel.from_pretrained(
+    "black-forest-labs/FLUX.1-dev",
+    subfolder="transformer",
+    quantization_config=quant_config,
++   torch_dtype=torch.float32,
+)
+```
 
-quantization_config = BitsAndBytesConfig(load_in_8bit=True)
+Let's generate an image using our quantized models.
 
-model_8bit = FluxTransformer2DModel.from_pretrained(
+Setting `device_map="auto"` automatically fills all available space on the GPU(s) first, then the
+CPU, and finally, the hard drive (the absolute slowest option) if there is still not enough memory.
+
+```py
+pipe = FluxPipeline.from_pretrained(
     "black-forest-labs/FLUX.1-dev",
-    subfolder="transformer",
-    quantization_config=quantization_config,
-    torch_dtype=torch.float32
+    transformer=transformer_8bit,
+    text_encoder_2=text_encoder_2_8bit,
+    torch_dtype=torch.float16,
+    device_map="auto",
 )
-model_8bit.transformer_blocks.layers[-1].norm2.weight.dtype
+
+pipe_kwargs = {
+    "prompt": "A cat holding a sign that says hello world",
+    "height": 1024,
+    "width": 1024,
+    "guidance_scale": 3.5,
+    "num_inference_steps": 50,
+    "max_sequence_length": 512,
+}
+
+image = pipe(**pipe_kwargs, generator=torch.manual_seed(0),).images[0]
 ```
 
-Once a model is quantized, you can push the model to the Hub with the [`~ModelMixin.push_to_hub`] method. The quantization `config.json` file is pushed first, followed by the quantized model weights. You can also save the serialized 4-bit models locally with [`~ModelMixin.save_pretrained`].
+<div class="flex justify-center">
+   <img src="https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/diffusers/quant-bnb/8bit.png"/>
+</div>
+
+When there is enough memory, you can also directly move the pipeline to the GPU with `.to("cuda")` and apply [`~DiffusionPipeline.enable_model_cpu_offload`] to optimize GPU memory usage.
+
+Once a model is quantized, you can push the model to the Hub with the [`~ModelMixin.push_to_hub`] method. The quantization `config.json` file is pushed first, followed by the quantized model weights. You can also save the serialized 8-bit models locally with [`~ModelMixin.save_pretrained`].
 
 </hfoption>
 <hfoption id="4-bit">
 
 Quantizing a model in 4-bit reduces your memory-usage by 4x:
 
+bitsandbytes is supported in both Transformers and Diffusers, so you can can quantize both the
+[`FluxTransformer2DModel`] and [`~transformers.T5EncoderModel`].
+
+For Ada and higher-series GPUs. we recommend changing `torch_dtype` to `torch.bfloat16`.
+
+> [!TIP]
+> The [`CLIPTextModel`] and [`AutoencoderKL`] aren't quantized because they're already small in size and because [`AutoencoderKL`] only has a few `torch.nn.Linear` layers.
+
 ```py
-from diffusers import FluxTransformer2DModel, BitsAndBytesConfig
+from diffusers import BitsAndBytesConfig as DiffusersBitsAndBytesConfig
+from transformers import BitsAndBytesConfig as TransformersBitsAndBytesConfig
 
-quantization_config = BitsAndBytesConfig(load_in_4bit=True)
+from diffusers import FluxTransformer2DModel
+from transformers import T5EncoderModel
 
-model_4bit = FluxTransformer2DModel.from_pretrained(
+quant_config = TransformersBitsAndBytesConfig(load_in_4bit=True,)
+
+text_encoder_2_4bit = T5EncoderModel.from_pretrained(
+    "black-forest-labs/FLUX.1-dev",
+    subfolder="text_encoder_2",
+    quantization_config=quant_config,
+    torch_dtype=torch.float16,
+)
+
+quant_config = DiffusersBitsAndBytesConfig(load_in_4bit=True,)
+
+transformer_4bit = FluxTransformer2DModel.from_pretrained(
     "black-forest-labs/FLUX.1-dev",
     subfolder="transformer",
-    quantization_config=quantization_config
+    quantization_config=quant_config,
+    torch_dtype=torch.float16,
 )
 ```
 
-By default, all the other modules such as `torch.nn.LayerNorm` are converted to `torch.float16`. You can change the data type of these modules with the `torch_dtype` parameter if you want:
+By default, all the other modules such as `torch.nn.LayerNorm` are converted to `torch.float16`. You can change the data type of these modules with the `torch_dtype` parameter.
 
-```py
-from diffusers import FluxTransformer2DModel, BitsAndBytesConfig
+```diff
+transformer_4bit = FluxTransformer2DModel.from_pretrained(
+    "black-forest-labs/FLUX.1-dev",
+    subfolder="transformer",
+    quantization_config=quant_config,
++   torch_dtype=torch.float32,
+)
+```
 
-quantization_config = BitsAndBytesConfig(load_in_4bit=True)
+Let's generate an image using our quantized models.
 
-model_4bit = FluxTransformer2DModel.from_pretrained(
+Setting `device_map="auto"` automatically fills all available space on the GPU(s) first, then the CPU, and finally, the hard drive (the absolute slowest option) if there is still not enough memory.
+
+```py
+pipe = FluxPipeline.from_pretrained(
     "black-forest-labs/FLUX.1-dev",
-    subfolder="transformer",
-    quantization_config=quantization_config,
-    torch_dtype=torch.float32
+    transformer=transformer_4bit,
+    text_encoder_2=text_encoder_2_4bit,
+    torch_dtype=torch.float16,
+    device_map="auto",
 )
-model_4bit.transformer_blocks.layers[-1].norm2.weight.dtype
+
+pipe_kwargs = {
+    "prompt": "A cat holding a sign that says hello world",
+    "height": 1024,
+    "width": 1024,
+    "guidance_scale": 3.5,
+    "num_inference_steps": 50,
+    "max_sequence_length": 512,
+}
+
+image = pipe(**pipe_kwargs, generator=torch.manual_seed(0),).images[0]
 ```
 
-Call [`~ModelMixin.push_to_hub`] after loading it in 4-bit precision. You can also save the serialized 4-bit models locally with [`~ModelMixin.save_pretrained`].  
+<div class="flex justify-center">
+   <img src="https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/diffusers/quant-bnb/4bit.png"/>
+</div>
+
+When there is enough memory, you can also directly move the pipeline to the GPU with `.to("cuda")` and apply [`~DiffusionPipeline.enable_model_cpu_offload`] to optimize GPU memory usage.
+
+Once a model is quantized, you can push the model to the Hub with the [`~ModelMixin.push_to_hub`] method. The quantization `config.json` file is pushed first, followed by the quantized model weights. You can also save the serialized 4-bit models locally with [`~ModelMixin.save_pretrained`].
 
 </hfoption>
 </hfoptions>
@@ -199,17 +302,34 @@ quantization_config = BitsAndBytesConfig(load_in_4bit=True, bnb_4bit_compute_dty
 NF4 is a 4-bit data type from the [QLoRA](https://hf.co/papers/2305.14314) paper, adapted for weights initialized from a normal distribution. You should use NF4 for training 4-bit base models. This can be configured with the `bnb_4bit_quant_type` parameter in the [`BitsAndBytesConfig`]:
 
 ```py
-from diffusers import BitsAndBytesConfig
+from diffusers import BitsAndBytesConfig as DiffusersBitsAndBytesConfig
+from transformers import BitsAndBytesConfig as TransformersBitsAndBytesConfig
 
-nf4_config = BitsAndBytesConfig(
+from diffusers import FluxTransformer2DModel
+from transformers import T5EncoderModel
+
+quant_config = TransformersBitsAndBytesConfig(
     load_in_4bit=True,
     bnb_4bit_quant_type="nf4",
 )
 
-model_nf4 = SD3Transformer2DModel.from_pretrained(
-    "stabilityai/stable-diffusion-3-medium-diffusers",
+text_encoder_2_4bit = T5EncoderModel.from_pretrained(
+    "black-forest-labs/FLUX.1-dev",
+    subfolder="text_encoder_2",
+    quantization_config=quant_config,
+    torch_dtype=torch.float16,
+)
+
+quant_config = DiffusersBitsAndBytesConfig(
+    load_in_4bit=True,
+    bnb_4bit_quant_type="nf4",
+)
+
+transformer_4bit = FluxTransformer2DModel.from_pretrained(
+    "black-forest-labs/FLUX.1-dev",
     subfolder="transformer",
-    quantization_config=nf4_config,
+    quantization_config=quant_config,
+    torch_dtype=torch.float16,
 )
 ```
 
@@ -220,38 +340,74 @@ For inference, the `bnb_4bit_quant_type` does not have a huge impact on performa
 Nested quantization is a technique that can save additional memory at no additional performance cost. This feature performs a second quantization of the already quantized weights to save an additional 0.4 bits/parameter. 
 
 ```py
-from diffusers import BitsAndBytesConfig
+from diffusers import BitsAndBytesConfig as DiffusersBitsAndBytesConfig
+from transformers import BitsAndBytesConfig as TransformersBitsAndBytesConfig
 
-double_quant_config = BitsAndBytesConfig(
+from diffusers import FluxTransformer2DModel
+from transformers import T5EncoderModel
+
+quant_config = TransformersBitsAndBytesConfig(
     load_in_4bit=True,
     bnb_4bit_use_double_quant=True,
 )
 
-double_quant_model = SD3Transformer2DModel.from_pretrained(
-    "stabilityai/stable-diffusion-3-medium-diffusers",
+text_encoder_2_4bit = T5EncoderModel.from_pretrained(
+    "black-forest-labs/FLUX.1-dev",
+    subfolder="text_encoder_2",
+    quantization_config=quant_config,
+    torch_dtype=torch.float16,
+)
+
+quant_config = DiffusersBitsAndBytesConfig(
+    load_in_4bit=True,
+    bnb_4bit_use_double_quant=True,
+)
+
+transformer_4bit = FluxTransformer2DModel.from_pretrained(
+    "black-forest-labs/FLUX.1-dev",
     subfolder="transformer",
-    quantization_config=double_quant_config,
+    quantization_config=quant_config,
+    torch_dtype=torch.float16,
 )
 ```
 
 ## Dequantizing `bitsandbytes` models
 
-Once quantized, you can dequantize the model to the original precision but this might result in a small quality loss of the model. Make sure you have enough GPU RAM to fit the dequantized model. 
+Once quantized, you can dequantize a model to its original precision, but this might result in a small loss of quality. Make sure you have enough GPU RAM to fit the dequantized model. 
 
 ```python
-from diffusers import BitsAndBytesConfig
+from diffusers import BitsAndBytesConfig as DiffusersBitsAndBytesConfig
+from transformers import BitsAndBytesConfig as TransformersBitsAndBytesConfig
 
-double_quant_config = BitsAndBytesConfig(
+from diffusers import FluxTransformer2DModel
+from transformers import T5EncoderModel
+
+quant_config = TransformersBitsAndBytesConfig(
     load_in_4bit=True,
     bnb_4bit_use_double_quant=True,
 )
 
-double_quant_model = SD3Transformer2DModel.from_pretrained(
-    "stabilityai/stable-diffusion-3-medium-diffusers",
+text_encoder_2_4bit = T5EncoderModel.from_pretrained(
+    "black-forest-labs/FLUX.1-dev",
+    subfolder="text_encoder_2",
+    quantization_config=quant_config,
+    torch_dtype=torch.float16,
+)
+
+quant_config = DiffusersBitsAndBytesConfig(
+    load_in_4bit=True,
+    bnb_4bit_use_double_quant=True,
+)
+
+transformer_4bit = FluxTransformer2DModel.from_pretrained(
+    "black-forest-labs/FLUX.1-dev",
     subfolder="transformer",
-    quantization_config=double_quant_config,
+    quantization_config=quant_config,
+    torch_dtype=torch.float16,
 )
-model.dequantize()
+
+text_encoder_2_4bit.dequantize()
+transformer_4bit.dequantize()
 ```
 
 ## Resources