Enable module state_dict compression, simplify compression logic (#302)

* use map_module_to_scheme, _should_save_zp

Signed-off-by: Kyle Sayers <kylesayrs@gmail.com>

* remove unused import

Signed-off-by: Kyle Sayers <kylesayrs@gmail.com>

* remove unused imports

Signed-off-by: Kyle Sayers <kylesayrs@gmail.com>

* rename to _skip_zp

Signed-off-by: Kyle Sayers <kylesayrs@gmail.com>

* type hint nit

Signed-off-by: Kyle Sayers <kylesayrs@gmail.com>

* safetensors function signature is weird

Signed-off-by: Kyle Sayers <kylesayrs@gmail.com>

---------

Signed-off-by: Kyle Sayers <kylesayrs@gmail.com>

Author: kylesayrs

src/compressed_tensors/compressors/model_compressors/model_compressor.py

@@ -19,7 +19,7 @@
 import re
 from contextlib import contextmanager
 from copy import deepcopy
-from typing import TYPE_CHECKING, Any, Dict, List, Optional, Set, Tuple, TypeVar, Union
+from typing import TYPE_CHECKING, Any, Dict, List, Optional, Set, TypeVar, Union
 
 import compressed_tensors
 import torch
@@ -36,12 +36,12 @@
 from compressed_tensors.quantization import (
     DEFAULT_QUANTIZATION_METHOD,
     QuantizationConfig,
+    QuantizationScheme,
     QuantizationStatus,
     apply_quantization_config,
     load_pretrained_quantization_parameters,
 )
 from compressed_tensors.quantization.lifecycle import expand_target_names
-from compressed_tensors.quantization.quant_args import QuantizationArgs
 from compressed_tensors.quantization.utils import (
     is_module_quantized,
     iter_named_leaf_modules,
@@ -64,7 +64,7 @@
 from transformers.file_utils import CONFIG_NAME
 
 
-__all__ = ["ModelCompressor", "map_modules_to_quant_args"]
+__all__ = ["ModelCompressor", "map_module_to_scheme"]
 
 _LOGGER: logging.Logger = logging.getLogger(__name__)
 
@@ -372,20 +372,17 @@ def compress(
         :param state_dict: optional uncompressed state_dict to insert into model
         :return: compressed state dict
         """
+
         if state_dict is None:
             state_dict = model.state_dict()
 
-        compressed_state_dict = state_dict
-
-        quantized_modules_to_args: Dict[
-            str, QuantizationArgs
-        ] = map_modules_to_quant_args(model)
-
         if self.quantization_compressor is not None:
-            compressed_state_dict = self.quantization_compressor.compress(
-                state_dict, names_to_scheme=quantized_modules_to_args
+            module_to_scheme = map_module_to_scheme(model)
+            state_dict = self.quantization_compressor.compress(
+                state_dict, names_to_scheme=module_to_scheme
             )
 
+            # TODO: consider sparse compression to also be compression
             if self.quantization_config.format != CompressionFormat.dense.value:
                 self.quantization_config.quantization_status = (
                     QuantizationStatus.COMPRESSED
@@ -397,8 +394,8 @@ def compress(
                 targets=self.sparsity_config.targets,
                 ignore=self.sparsity_config.ignore,
             )
-            compressed_state_dict = self.sparsity_compressor.compress(
-                compressed_state_dict,
+            state_dict = self.sparsity_compressor.compress(
+                state_dict,
                 compression_targets=sparse_compression_targets,
             )
 
@@ -407,7 +404,7 @@ def compress(
         # https://github.com/huggingface/transformers/pull/30488
         transformers.modeling_utils.dtype_byte_size = new_dtype_byte_size
 
-        return compressed_state_dict
+        return state_dict
 
     def decompress(self, model_path: str, model: Module):
         """
@@ -605,30 +602,15 @@ def _replace_weights(self, dense_weight_generator, model: Module):
                         update_parameter_data(module, param_data, param_name)
 
 
-def map_modules_to_quant_args(
-    model: Module,
-) -> Dict[str, Union[QuantizationArgs, Tuple[QuantizationArgs, QuantizationArgs]]]:
+def map_module_to_scheme(model: Module) -> Dict[str, QuantizationScheme]:
     """
-    Given a pytorch model, map out the submodule name (usually linear layers)
-    to the weight QuantizationArgs. If running input activation quantization, will also
-    map to the input QuantizationArgs in a tuple.
-
-    :param model: pytorch model
+    Returns a dictionary which maps quantized module names to their quantization schemes
     """
-    quantized_modules_to_args = {}
-    for name, submodule in iter_named_leaf_modules(model):
-        if is_module_quantized(submodule):
-            if submodule.quantization_scheme.weights is not None:
-                name = fix_fsdp_module_name(name)
-                quantized_modules_to_args[name] = submodule.quantization_scheme.weights
-                if submodule.quantization_scheme.input_activations is not None:
-                    weight_args = quantized_modules_to_args.get(name)
-                    quantized_modules_to_args[name] = (
-                        weight_args,
-                        submodule.quantization_scheme.input_activations,
-                    )
-
-    return quantized_modules_to_args
+    return {
+        fix_fsdp_module_name(name): module.quantization_scheme
+        for name, module in iter_named_leaf_modules(model)
+        if is_module_quantized(module)
+    }
 
 
 # HACK: Override the dtype_byte_size function in transformers to support float8 types

src/compressed_tensors/compressors/quantized_compressors/base.py

@@ -14,15 +14,16 @@
 
 import logging
 from pathlib import Path
-from typing import Any, Dict, Generator, Optional, Tuple, Union
+from typing import Any, Dict, Generator, Tuple, Union
 
 import torch
 from compressed_tensors.compressors.base import BaseCompressor
-from compressed_tensors.quantization import QuantizationArgs, QuantizationStrategy
+from compressed_tensors.quantization import QuantizationScheme, QuantizationStrategy
 from compressed_tensors.utils import (
     get_nested_mappings_from_state_dict,
     get_nested_weight_mappings,
     merge_names,
+    remove_suffix,
 )
 from safetensors import safe_open
 from torch import Tensor
@@ -69,7 +70,7 @@ class BaseQuantizationCompressor(BaseCompressor):
     def compress(
         self,
         model_state: Dict[str, Tensor],
-        names_to_scheme: Dict[str, QuantizationArgs],
+        names_to_scheme: Dict[str, QuantizationScheme],
         **kwargs,
     ) -> Dict[str, Tensor]:
         """
@@ -81,87 +82,87 @@ def compress(
         :return: compressed state dict
         """
         compressed_dict = {}
-        weight_suffix = ".weight"
-        input_zp_suffix = ".input_zero_point"
-        weight_zp_suffix = ".weight_zero_point"
-        _LOGGER.debug(
-            f"Compressing model with {len(model_state)} parameterized layers..."
-        )
+        save_device = "cpu"
+
+        uncompressed_names = list(model_state.keys())
+        for name in tqdm(uncompressed_names, desc="Compressing with quantization"):
+            value = model_state[name]
+
+            # compress weights
+            if name.endswith("weight"):
+                prefix = remove_suffix(name, "weight")
+
+                # gather qparams
+                scale = model_state.get(prefix + "weight_scale", None)
+                g_idx = model_state.get(prefix + "weight_g_idx", None)
+                zp = model_state.get(prefix + "weight_zero_point", None)
+
+                # is scale does not exist, then weight cannot be compressed
+                if scale is None:
+                    compressed_dict[name] = value.to(save_device)
+                    continue
+
+                # compress values on cpu (memory movement too expensive)
+                module_path = prefix[:-1] if prefix.endswith(".") else prefix
+                quant_args = names_to_scheme[module_path].weights
+                compressed_values = self.compress_weight(
+                    weight=value,
+                    scale=scale,
+                    zero_point=zp,
+                    g_idx=g_idx,
+                    quantization_args=quant_args,
+                    device="cpu",
+                )
+
+                # update state dict
+                for key, value in compressed_values.items():
+                    compressed_dict[prefix + key] = value.to(save_device)
 
-        for name, value in tqdm(model_state.items(), desc="Quantized Compression"):
-            # check if the parameter we're compressing is the weight zp
-            # or the input zp
-            is_weight_zp = name.endswith(weight_zp_suffix)
-            is_input_zp = name.endswith(input_zp_suffix)
-
-            # if we're saving the weight zp, fetch weight quant args
-            if is_weight_zp:
-                quant_args_zp = names_to_scheme.get(name[: -(len(weight_zp_suffix))])
-                if isinstance(quant_args_zp, tuple):
-                    # If tuple, first value is weight args, second is input args
-                    quant_args_zp = quant_args_zp[0]
-
-            # if we're saving the input zp, fetch input quant args
-            if is_input_zp:
-                input_args_zp = names_to_scheme.get(name[: -(len(input_zp_suffix))])
-                if isinstance(input_args_zp, tuple):
-                    # If tuple, first value is weight args, second is input args
-                    input_args_zp = input_args_zp[-1]
-
-            if name.endswith(weight_suffix):
-                prefix = name[: -(len(weight_suffix))]
-                scale = model_state.get(merge_names(prefix, "weight_scale"), None)
-                zp = model_state.get(merge_names(prefix, "weight_zero_point"), None)
-                g_idx = model_state.get(merge_names(prefix, "weight_g_idx"), None)
-                if scale is not None:
-                    # weight is quantized, compress it
-                    if isinstance(names_to_scheme[prefix], tuple):
-                        quant_args = names_to_scheme[prefix][0]
-                    else:
-                        quant_args = names_to_scheme[prefix]
-
-                    compressed_data = self.compress_weight(
-                        weight=value,
-                        scale=scale,
-                        zero_point=zp,
-                        g_idx=g_idx,
-                        quantization_args=quant_args,
-                        device="cpu",
-                    )
-                    for key, value in compressed_data.items():
-                        compressed_dict[merge_names(prefix, key)] = value
-                else:
-                    compressed_dict[name] = value.to("cpu")
-            # only save zp if asym and not packed zp
-            elif is_weight_zp and (
-                quant_args_zp.symmetric or self._check_if_zp_pack_quantized(quant_args)
-            ):
-                continue
-            # only save if asym
-            elif is_input_zp and input_args_zp.symmetric:
-                continue
-            elif name.endswith("g_idx") and torch.any(value <= -1):
-                continue
             else:
-                compressed_dict[name] = value.to("cpu")
+                # omit saving zero points for symmetric or packed quantization
+                if name.endswith("zero_point") and self._skip_zp(name, names_to_scheme):
+                    continue
+
+                # omit saving for g_idx if uninitialized
+                # TODO: does this case actually occur?
+                elif name.endswith("g_idx") and torch.any(value <= -1):
+                    continue
+
+                compressed_dict[name] = value.to(save_device)
 
         return compressed_dict
 
-    def _check_if_zp_pack_quantized(self, quant_args):
+    def _skip_zp(
+        self, name: str, names_to_scheme: Dict[str, QuantizationScheme]
+    ) -> bool:
         from compressed_tensors.compressors import PackedQuantizationCompressor
 
-        if isinstance(self, PackedQuantizationCompressor):
-            if not quant_args.symmetric and quant_args.strategy in [
-                QuantizationStrategy.GROUP.value,
-                QuantizationStrategy.CHANNEL.value,
-            ]:
-                return True
-        return False
+        module_name, zp_name = name.rsplit(".", 1) if "." in name else ("", name)
+        scheme = names_to_scheme[module_name]
+
+        if zp_name == "weight_zero_point":
+            args = scheme.weights
+        if zp_name == "input_zero_point":
+            args = scheme.input_activations
+        if zp_name == "output_zero_point":
+            args = scheme.output_activations
+
+        symmetric = args.symmetric
+        packable_strategies = [
+            QuantizationStrategy.GROUP.value,
+            QuantizationStrategy.CHANNEL.value,
+        ]
+        packed = (
+            isinstance(self, PackedQuantizationCompressor)
+            and args.strategy in packable_strategies
+        )
+
+        return symmetric or packed
 
     def decompress(
         self,
         path_to_model_or_tensors: Union[str, Path, Dict[str, Any]],
-        names_to_scheme: Dict[str, QuantizationArgs],
+        names_to_scheme: Dict[str, QuantizationScheme],
         device: str = "cpu",
     ) -> Generator[Tuple[str, Tensor], None, None]:
         """
@@ -170,8 +171,9 @@ def decompress(
         dense state dict
         :param path_to_model_or_tensors: path to compressed safetensors model (directory
             with one or more safetensors files) or compressed tensors file
-        :param names_to_scheme: quantization args for each quantized weight
-        :param device: optional device to load intermediate weights into
+        :param names_to_scheme: quantization scheme for each quantized weight
+        :param device: optional device to load intermediate weights into (must be `str`,
+            not `torch.device`)
         :return: compressed state dict
         """
         if isinstance(path_to_model_or_tensors, (str, Path)):
@@ -184,7 +186,12 @@ def decompress(
                 path_to_model_or_tensors, names_to_scheme
             )
 
-    def _decompress_from_path(self, path_to_model, names_to_scheme, device):
+    def _decompress_from_path(
+        self,
+        path_to_model: Union[str, Path, Dict[str, Any]],
+        names_to_scheme: Dict[str, QuantizationScheme],
+        device: str,
+    ):
         weight_mappings = get_nested_weight_mappings(
             path_to_model, self.compression_param_names
         )
@@ -195,7 +202,7 @@ def _decompress_from_path(self, path_to_model, names_to_scheme, device):
                 with safe_open(safe_path, framework="pt", device=device) as f:
                     weight_data[param_name] = f.get_tensor(full_name)
             if "weight_scale" in weight_data:
-                quant_args = names_to_scheme[weight_name]
+                quant_args = names_to_scheme[weight_name].weights
                 decompressed = self.decompress_weight(
                     compressed_data=weight_data, quantization_args=quant_args
                 )