mmpretrain/models/backbones/convnext.py

# Copyright (c) OpenMMLab. All rights reserved.
from functools import partial
from itertools import chain
from typing import Sequence

import torch
import torch.nn as nn
import torch.utils.checkpoint as cp
from mmcv.cnn.bricks import DropPath
from mmengine.model import BaseModule, ModuleList, Sequential

from mmpretrain.registry import MODELS
from ..utils import GRN, build_norm_layer
from .base_backbone import BaseBackbone


class ConvNeXtBlock(BaseModule):
    """ConvNeXt Block.

    Args:
        in_channels (int): The number of input channels.
        dw_conv_cfg (dict): Config of depthwise convolution.
            Defaults to ``dict(kernel_size=7, padding=3)``.
        norm_cfg (dict): The config dict for norm layers.
            Defaults to ``dict(type='LN2d', eps=1e-6)``.
        act_cfg (dict): The config dict for activation between pointwise
            convolution. Defaults to ``dict(type='GELU')``.
        mlp_ratio (float): The expansion ratio in both pointwise convolution.
            Defaults to 4.
        linear_pw_conv (bool): Whether to use linear layer to do pointwise
            convolution. More details can be found in the note.
            Defaults to True.
        drop_path_rate (float): Stochastic depth rate. Defaults to 0.
        layer_scale_init_value (float): Init value for Layer Scale.
            Defaults to 1e-6.

    Note:
        There are two equivalent implementations:

        1. DwConv -> LayerNorm -> 1x1 Conv -> GELU -> 1x1 Conv;
           all outputs are in (N, C, H, W).
        2. DwConv -> LayerNorm -> Permute to (N, H, W, C) -> Linear -> GELU
           -> Linear; Permute back

        As default, we use the second to align with the official repository.
        And it may be slightly faster.
    """

    def __init__(self,
                 in_channels,
                 dw_conv_cfg=dict(kernel_size=7, padding=3),
                 norm_cfg=dict(type='LN2d', eps=1e-6),
                 act_cfg=dict(type='GELU'),
                 mlp_ratio=4.,
                 linear_pw_conv=True,
                 drop_path_rate=0.,
                 layer_scale_init_value=1e-6,
                 use_grn=False,
                 with_cp=False):
        super().__init__()
        self.with_cp = with_cp

        self.depthwise_conv = nn.Conv2d(
            in_channels, in_channels, groups=in_channels, **dw_conv_cfg)

        self.linear_pw_conv = linear_pw_conv
        self.norm = build_norm_layer(norm_cfg, in_channels)

        mid_channels = int(mlp_ratio * in_channels)
        if self.linear_pw_conv:
            # Use linear layer to do pointwise conv.
            pw_conv = nn.Linear
        else:
            pw_conv = partial(nn.Conv2d, kernel_size=1)

        self.pointwise_conv1 = pw_conv(in_channels, mid_channels)
        self.act = MODELS.build(act_cfg)
        self.pointwise_conv2 = pw_conv(mid_channels, in_channels)

        if use_grn:
            self.grn = GRN(mid_channels)
        else:
            self.grn = None

        self.gamma = nn.Parameter(
            layer_scale_init_value * torch.ones((in_channels)),
            requires_grad=True) if layer_scale_init_value > 0 else None

        self.drop_path = DropPath(
            drop_path_rate) if drop_path_rate > 0. else nn.Identity()

    def forward(self, x):

        def _inner_forward(x):
            shortcut = x
            x = self.depthwise_conv(x)

            if self.linear_pw_conv:
                x = x.permute(0, 2, 3, 1)  # (N, C, H, W) -> (N, H, W, C)
                x = self.norm(x, data_format='channel_last')
                x = self.pointwise_conv1(x)
                x = self.act(x)
                if self.grn is not None:
                    x = self.grn(x, data_format='channel_last')
                x = self.pointwise_conv2(x)
                x = x.permute(0, 3, 1, 2)  # (N, H, W, C) -> (N, C, H, W)
            else:
                x = self.norm(x, data_format='channel_first')
                x = self.pointwise_conv1(x)
                x = self.act(x)

                if self.grn is not None:
                    x = self.grn(x, data_format='channel_first')
                x = self.pointwise_conv2(x)

            if self.gamma is not None:
                x = x.mul(self.gamma.view(1, -1, 1, 1))

            x = shortcut + self.drop_path(x)
            return x

        if self.with_cp and x.requires_grad:
            x = cp.checkpoint(_inner_forward, x)
        else:
            x = _inner_forward(x)
        return x


@MODELS.register_module()
class ConvNeXt(BaseBackbone):
    """ConvNeXt v1&v2 backbone.

    A PyTorch implementation of `A ConvNet for the 2020s
    <https://arxiv.org/abs/2201.03545>`_ and
    `ConvNeXt V2: Co-designing and Scaling ConvNets with Masked Autoencoders
    <http://arxiv.org/abs/2301.00808>`_

    Modified from the `official repo
    <https://github.com/facebookresearch/ConvNeXt/blob/main/models/convnext.py>`_
    and `timm
    <https://github.com/rwightman/pytorch-image-models/blob/master/timm/models/convnext.py>`_.

    To use ConvNeXt v2, please set ``use_grn=True`` and ``layer_scale_init_value=0.``.

    Args:
        arch (str | dict): The model's architecture. If string, it should be
            one of architecture in ``ConvNeXt.arch_settings``. And if dict, it
            should include the following two keys:

            - depths (list[int]): Number of blocks at each stage.
            - channels (list[int]): The number of channels at each stage.

            Defaults to 'tiny'.
        in_channels (int): Number of input image channels. Defaults to 3.
        stem_patch_size (int): The size of one patch in the stem layer.
            Defaults to 4.
        norm_cfg (dict): The config dict for norm layers.
            Defaults to ``dict(type='LN2d', eps=1e-6)``.
        act_cfg (dict): The config dict for activation between pointwise
            convolution. Defaults to ``dict(type='GELU')``.
        linear_pw_conv (bool): Whether to use linear layer to do pointwise
            convolution. Defaults to True.
        use_grn (bool): Whether to add Global Response Normalization in the
            blocks. Defaults to False.
        drop_path_rate (float): Stochastic depth rate. Defaults to 0.
        layer_scale_init_value (float): Init value for Layer Scale.
            Defaults to 1e-6.
        out_indices (Sequence | int): Output from which stages.
            Defaults to -1, means the last stage.
        frozen_stages (int): Stages to be frozen (all param fixed).
            Defaults to 0, which means not freezing any parameters.
        gap_before_final_norm (bool): Whether to globally average the feature
            map before the final norm layer. In the official repo, it's only
            used in classification task. Defaults to True.
        with_cp (bool): Use checkpoint or not. Using checkpoint will save some
            memory while slowing down the training speed. Defaults to False.
        init_cfg (dict, optional): Initialization config dict
    """  # noqa: E501
    arch_settings = {
        'atto': {
            'depths': [2, 2, 6, 2],
            'channels': [40, 80, 160, 320]
        },
        'femto': {
            'depths': [2, 2, 6, 2],
            'channels': [48, 96, 192, 384]
        },
        'pico': {
            'depths': [2, 2, 6, 2],
            'channels': [64, 128, 256, 512]
        },
        'nano': {
            'depths': [2, 2, 8, 2],
            'channels': [80, 160, 320, 640]
        },
        'tiny': {
            'depths': [3, 3, 9, 3],
            'channels': [96, 192, 384, 768]
        },
        'small': {
            'depths': [3, 3, 27, 3],
            'channels': [96, 192, 384, 768]
        },
        'base': {
            'depths': [3, 3, 27, 3],
            'channels': [128, 256, 512, 1024]
        },
        'large': {
            'depths': [3, 3, 27, 3],
            'channels': [192, 384, 768, 1536]
        },
        'xlarge': {
            'depths': [3, 3, 27, 3],
            'channels': [256, 512, 1024, 2048]
        },
        'huge': {
            'depths': [3, 3, 27, 3],
            'channels': [352, 704, 1408, 2816]
        }
    }

    def __init__(self,
                 arch='tiny',
                 in_channels=3,
                 stem_patch_size=4,
                 norm_cfg=dict(type='LN2d', eps=1e-6),
                 act_cfg=dict(type='GELU'),
                 linear_pw_conv=True,
                 use_grn=False,
                 drop_path_rate=0.,
                 layer_scale_init_value=1e-6,
                 out_indices=-1,
                 frozen_stages=0,
                 gap_before_final_norm=True,
                 with_cp=False,
                 init_cfg=[
                     dict(
                         type='TruncNormal',
                         layer=['Conv2d', 'Linear'],
                         std=.02,
                         bias=0.),
                     dict(
                         type='Constant', layer=['LayerNorm'], val=1.,
                         bias=0.),
                 ]):
        super().__init__(init_cfg=init_cfg)

        if isinstance(arch, str):
            assert arch in self.arch_settings, \
                f'Unavailable arch, please choose from ' \
                f'({set(self.arch_settings)}) or pass a dict.'
            arch = self.arch_settings[arch]
        elif isinstance(arch, dict):
            assert 'depths' in arch and 'channels' in arch, \
                f'The arch dict must have "depths" and "channels", ' \
                f'but got {list(arch.keys())}.'

        self.depths = arch['depths']
        self.channels = arch['channels']
        assert (isinstance(self.depths, Sequence)
                and isinstance(self.channels, Sequence)
                and len(self.depths) == len(self.channels)), \
            f'The "depths" ({self.depths}) and "channels" ({self.channels}) ' \
            'should be both sequence with the same length.'

        self.num_stages = len(self.depths)

        if isinstance(out_indices, int):
            out_indices = [out_indices]
        assert isinstance(out_indices, Sequence), \
            f'"out_indices" must by a sequence or int, ' \
            f'get {type(out_indices)} instead.'
        for i, index in enumerate(out_indices):
            if index < 0:
                out_indices[i] = 4 + index
                assert out_indices[i] >= 0, f'Invalid out_indices {index}'
        self.out_indices = out_indices

        self.frozen_stages = frozen_stages
        self.gap_before_final_norm = gap_before_final_norm

        # stochastic depth decay rule
        dpr = [
            x.item()
            for x in torch.linspace(0, drop_path_rate, sum(self.depths))
        ]
        block_idx = 0

        # 4 downsample layers between stages, including the stem layer.
        self.downsample_layers = ModuleList()
        stem = nn.Sequential(
            nn.Conv2d(
                in_channels,
                self.channels[0],
                kernel_size=stem_patch_size,
                stride=stem_patch_size),
            build_norm_layer(norm_cfg, self.channels[0]),
        )
        self.downsample_layers.append(stem)

        # 4 feature resolution stages, each consisting of multiple residual
        # blocks
        self.stages = nn.ModuleList()

        for i in range(self.num_stages):
            depth = self.depths[i]
            channels = self.channels[i]

            if i >= 1:
                downsample_layer = nn.Sequential(
                    build_norm_layer(norm_cfg, self.channels[i - 1]),
                    nn.Conv2d(
                        self.channels[i - 1],
                        channels,
                        kernel_size=2,
                        stride=2),
                )
                self.downsample_layers.append(downsample_layer)

            stage = Sequential(*[
                ConvNeXtBlock(
                    in_channels=channels,
                    drop_path_rate=dpr[block_idx + j],
                    norm_cfg=norm_cfg,
                    act_cfg=act_cfg,
                    linear_pw_conv=linear_pw_conv,
                    layer_scale_init_value=layer_scale_init_value,
                    use_grn=use_grn,
                    with_cp=with_cp) for j in range(depth)
            ])
            block_idx += depth

            self.stages.append(stage)

            if i in self.out_indices:
                norm_layer = build_norm_layer(norm_cfg, channels)
                self.add_module(f'norm{i}', norm_layer)

        self._freeze_stages()

    def forward(self, x):
        outs = []
        for i, stage in enumerate(self.stages):
            x = self.downsample_layers[i](x)
            x = stage(x)
            if i in self.out_indices:
                norm_layer = getattr(self, f'norm{i}')
                if self.gap_before_final_norm:
                    gap = x.mean([-2, -1], keepdim=True)
                    outs.append(norm_layer(gap).flatten(1))
                else:
                    outs.append(norm_layer(x))

        return tuple(outs)

    def _freeze_stages(self):
        for i in range(self.frozen_stages):
            downsample_layer = self.downsample_layers[i]
            stage = self.stages[i]
            downsample_layer.eval()
            stage.eval()
            for param in chain(downsample_layer.parameters(),
                               stage.parameters()):
                param.requires_grad = False

    def train(self, mode=True):
        super(ConvNeXt, self).train(mode)
        self._freeze_stages()

    def get_layer_depth(self, param_name: str, prefix: str = ''):
        """Get the layer-wise depth of a parameter.

        Args:
            param_name (str): The name of the parameter.
            prefix (str): The prefix for the parameter.
                Defaults to an empty string.

        Returns:
            Tuple[int, int]: The layer-wise depth and the num of layers.
        """

        max_layer_id = 12 if self.depths[-2] > 9 else 6

        if not param_name.startswith(prefix):
            # For subsequent module like head
            return max_layer_id + 1, max_layer_id + 2

        param_name = param_name[len(prefix):]
        if param_name.startswith('downsample_layers'):
            stage_id = int(param_name.split('.')[1])
            if stage_id == 0:
                layer_id = 0
            elif stage_id == 1 or stage_id == 2:
                layer_id = stage_id + 1
            else:  # stage_id == 3:
                layer_id = max_layer_id

        elif param_name.startswith('stages'):
            stage_id = int(param_name.split('.')[1])
            block_id = int(param_name.split('.')[2])
            if stage_id == 0 or stage_id == 1:
                layer_id = stage_id + 1
            elif stage_id == 2:
                layer_id = 3 + block_id // 3
            else:  # stage_id == 3:
                layer_id = max_layer_id

        # final norm layer
        else:
            layer_id = max_layer_id + 1

        return layer_id, max_layer_id + 2