Add documentation section about LoRA (vllm-project#2834)

docs/source/index.rst

@@ -82,6 +82,7 @@ Documentation
    models/supported_models
    models/adding_model
    models/engine_args
+   models/lora
 
 .. toctree::
    :maxdepth: 1

docs/source/models/lora.rst

@@ -0,0 +1,52 @@
+.. _lora:
+
+Using LoRA adapters
+===================
+
+This document shows you how to use `LoRA adapters <https://arxiv.org/abs/2106.09685>`_ with vLLM on top of a base model.
+Adapters can be efficiently served on a per request basis with minimal overhead. First we download the adapter(s) and save
+them locally with
+
+.. code-block:: python
+
+    from huggingface_hub import snapshot_download
+
+    sql_lora_path = snapshot_download(repo_id="yard1/llama-2-7b-sql-lora-test")
+
+
+Then we instantiate the base model and pass in the ``enable_lora=True`` flag:
+
+.. code-block:: python
+
+    from vllm import LLM, SamplingParams
+    from vllm.lora.request import LoRARequest
+
+    llm = LLM(model="meta-llama/Llama-2-7b-hf", enable_lora=True)
+
+
+We can now submit the prompts and call ``llm.generate`` with the ``lora_request`` parameter. The first parameter
+of ``LoRARequest`` is a human identifiable name, the second parameter is a globally unique ID for the adapter and
+the third parameter is the path to the LoRA adapter.
+
+.. code-block:: python
+
+    sampling_params = SamplingParams(
+        temperature=0,
+        max_tokens=256,
+        stop=["[/assistant]"]
+    )
+
+    prompts = [
+         "[user] Write a SQL query to answer the question based on the table schema.\n\n context: CREATE TABLE table_name_74 (icao VARCHAR, airport VARCHAR)\n\n question: Name the ICAO for lilongwe international airport [/user] [assistant]",
+         "[user] Write a SQL query to answer the question based on the table schema.\n\n context: CREATE TABLE table_name_11 (nationality VARCHAR, elector VARCHAR)\n\n question: When Anchero Pantaleone was the elector what is under nationality? [/user] [assistant]",
+    ]
+
+    outputs = llm.generate(
+        prompts,
+        sampling_params,
+        lora_request=LoRARequest("sql_adapter", 1, sql_lora_path)
+    )
+
+
+Check out `examples/multilora_inference.py <https://github.com/vllm-project/vllm/blob/main/examples/multilora_inference.py>`_
+for an example of how to use LoRA adapters with the async engine and how to use more advanced configuration options.