Allow Peft models to share their base model

docs/model_support.md

@@ -30,7 +30,11 @@
 - [baichuan-inc/baichuan-7B](https://huggingface.co/baichuan-inc/baichuan-7B)
 - [internlm/internlm-chat-7b](https://huggingface.co/internlm/internlm-chat-7b)
 - Any [EleutherAI](https://huggingface.co/EleutherAI) pythia model such as [pythia-6.9b](https://huggingface.co/EleutherAI/pythia-6.9b)
-- Any [Peft](https://github.com/huggingface/peft) adapter trained ontop of a model above.  To activate, must have `peft` in the model path.
+- Any [Peft](https://github.com/huggingface/peft) adapter trained ontop of a
+  model above.  To activate, must have `peft` in the model path.  Note: If
+  loading multiple peft models, you can have them share the base model weights by
+  setting the environment variable `PEFT_SHARE_BASE_WEIGHTS=true` in any model
+  worker.
 
 ## How to support a new model
 

fastchat/model/model_adapter.py

@@ -2,7 +2,7 @@
 
 import math
 import sys
-from typing import List, Optional
+from typing import Dict, List, Optional
 import warnings
 
 if sys.version_info >= (3, 9):
@@ -11,6 +11,7 @@
     from functools import lru_cache as cache
 
 import accelerate
+import os
 import psutil
 import torch
 from transformers import (
@@ -35,6 +36,12 @@
 )
 from fastchat.utils import get_gpu_memory
 
+# Check an environment variable to check if we should be sharing Peft model
+# weights.  When false we treat all Peft models as separate.
+peft_share_base_weights = (
+    os.environ.get("PEFT_SHARE_BASE_WEIGHTS", "false").lower() == "true"
+)
+
 
 class BaseModelAdapter:
     """The base and the default model adapter."""
@@ -254,6 +261,33 @@ def get_generate_stream_function(model: torch.nn.Module, model_path: str):
         return generate_stream_falcon
     elif is_codet5p:
         return generate_stream_codet5p
+    elif peft_share_base_weights and "peft" in model_path:
+        # Return a curried stream function that loads the right adapter
+        # according to the model_name available in this context.  This ensures
+        # the right weights are available.
+        @torch.inference_mode()
+        def generate_stream_peft(
+            model,
+            tokenizer,
+            params: Dict,
+            device: str,
+            context_len: int,
+            stream_interval: int = 2,
+            judge_sent_end: bool = False,
+        ):
+            model.set_adapter(model_path)
+            for x in generate_stream(
+                model,
+                tokenizer,
+                params,
+                device,
+                context_len,
+                stream_interval,
+                judge_sent_end,
+            ):
+                yield x
+
+        return generate_stream_peft
     else:
         return generate_stream
 
@@ -331,6 +365,9 @@ def remove_parent_directory_name(model_path):
     return model_path.split("/")[-1]
 
 
+peft_model_cache = {}
+
+
 class PeftModelAdapter:
     """Loads any "peft" model and it's base model."""
 
@@ -349,12 +386,42 @@ def load_model(self, model_path: str, from_pretrained_kwargs: dict):
                 f"PeftModelAdapter cannot load a base model with 'peft' in the name: {config.base_model_name_or_path}"
             )
 
+        # Basic proof of concept for loading peft adapters that share the base
+        # weights.  This is pretty messy because Peft re-writes the underlying
+        # base model and internally stores a map of adapter layers.
+        # So, to make this work we:
+        #  1. Cache the first peft model loaded for a given base models.
+        #  2. Call `load_model` for any follow on Peft models.
+        #  3. Make sure we load the adapters by the model_path.  Why? This is
+        #  what's accessible during inference time.
+        #  4. In get_generate_stream_function, make sure we load the right
+        #  adapter before doing inference.  This *should* be safe when calls
+        #  are blocked the same semaphore.
+        if peft_share_base_weights:
+            if base_model_path in peft_model_cache:
+                model, tokenizer = peft_model_cache[base_model_path]
+                # Super important: make sure we use model_path as the
+                # `adapter_name`.
+                model.load_adapter(model_path, adapter_name=model_path)
+            else:
+                base_adapter = get_model_adapter(base_model_path)
+                base_model, tokenizer = base_adapter.load_model(
+                    base_model_path, from_pretrained_kwargs
+                )
+                # Super important: make sure we use model_path as the
+                # `adapter_name`.
+                model = PeftModel.from_pretrained(
+                    base_model, model_path, adapter_name=model_path
+                )
+                peft_model_cache[base_model_path] = (model, tokenizer)
+            return model, tokenizer
+
+        # In the normal case, load up the base model weights again.
         base_adapter = get_model_adapter(base_model_path)
         base_model, tokenizer = base_adapter.load_model(
             base_model_path, from_pretrained_kwargs
         )
         model = PeftModel.from_pretrained(base_model, model_path)
-
         return model, tokenizer
 
     def get_default_conv_template(self, model_path: str) -> Conversation: