chunk_codegen.py

import colossalai
import torch
import copy
from typing import List, Callable, Any, Tuple, Dict, Iterable

from torch.fx.node import Node, Argument, map_arg, _type_repr, _get_qualified_name
from torch.fx.graph import (
    _Namespace,
    PythonCode,
    _custom_builtins,
    _is_from_torch,
    _format_target,
    magic_methods,
    CodeGen,
    _origin_type_map,
    inplace_methods,
    _CustomBuiltin,
)
from colossalai.fx.profiler import (
    calculate_fwd_out,
    calculate_fwd_tmp,
    parameter_size,
    activation_size,
)

CODEGEN_AVAILABLE = True
__all__ = ["ChunkCodeGen"]


def _delete_free_var_from_last_use(user_to_last_uses):
    for key, value in user_to_last_uses.items():
        for n in value:
            if n.op == "placeholder":
                user_to_last_uses[key].remove(n)


def _get_node_shape(node):
    if hasattr(node.meta["tensor_meta"], "shape"):
        return node.meta["tensor_meta"].shape
    return None


def _is_non_compute_node(node):
    if any(i in node.op for i in ["placeholder", "get_attr", "output"]) or any(
        i in node.name for i in ["getitem", "getattr"]
    ):
        return True
    return False


def _is_non_compute_node_except_placeholder(node):
    if any(i in node.op for i in ["get_attr", "output"]) or any(
        i in node.name for i in ["getitem", "getattr"]
    ):
        return True
    return False


def _is_non_compute_node_except_placeholder_output(node):
    if any(i in node.op for i in ["get_attr"]) or any(
        i in node.name for i in ["getitem", "getattr"]
    ):
        return True
    return False


class IndexTracer(object):
    def __init__(self, node_list) -> None:
        self.node_list = node_list
        self.idx_trace_list = self._init_idx_trace_list()
        self.idx_trace_equal = []
        self.idx_view_list = {}
        self.idx_count = -1
        self.all_reorder_map = {i: i for i in range(len(self.idx_trace_list))}

    def _init_idx_trace_list(self):
        idx_trace_list = []
        for n in self.node_list:
            if _get_node_shape(n) != None:
                cur_trace = {
                    "idx": [None for _ in range(len(_get_node_shape(n)))],
                    "compute": [[] for _ in range(len(_get_node_shape(n)))],
                    "source": [{} for _ in range(len(_get_node_shape(n)))],
                }
            else:
                cur_trace = {"idx": [], "compute": [], "source": []}
            idx_trace_list.append(cur_trace)
        return idx_trace_list

    def _add_index(self):
        """
        Update the count and return it. To record the idx number.

        Returns:
            idx_count: int
        """
        self.idx_count += 1
        return self.idx_count

    def _del_dim(self, idx, dim_idx):
        self.idx_trace_list[idx]["idx"].pop(dim_idx)
        self.idx_trace_list[idx]["compute"].pop(dim_idx)
        self.idx_trace_list[idx]["source"].pop(dim_idx)

    def _add_dim(self, node_idx, dim_idx):
        self.idx_trace_list[node_idx]["idx"].insert(dim_idx, self._add_index())
        self.idx_trace_list[node_idx]["compute"].insert(dim_idx, [])
        self.idx_trace_list[node_idx]["source"].insert(dim_idx, {})

    def _transform_index(self, node, node_dim):
        node_idx = self._find_idx_trace_from_node(node)
        dims = list(range(len(node_idx)))
        return dims[node_dim]

    def _inherit_index(self, node_from, node_from_dim, node_to, node_to_dim):
        node_from_dim = self._transform_index(node_from, node_from_dim)
        node_to_dim = self._transform_index(node_to, node_to_dim)
        node_from_trace = self._find_trace_from_node(node_from)
        node_to_trace = self._find_trace_from_node(node_to)
        node_to_trace["idx"][node_to_dim] = node_from_trace["idx"][node_from_dim]
        node_to_trace["compute"][node_to_dim] = copy.deepcopy(
            node_from_trace["compute"][node_from_dim]
        )
        self._add_source(node_from, node_from_dim, node_to, node_to_dim, init=True)

    def _inherit_all_computation(self, node_from, node_to):
        node_from_compute = self._find_compute_trace_from_node(node_from)
        node_to_compute = self._find_compute_trace_from_node(node_to)
        assert len(node_from_compute) == len(node_to_compute)
        for i in range(len(node_from_compute)):
            self._add_source(node_from, i, node_to, i)
            node_to_compute[i] = copy.deepcopy(node_from_compute[i])

    def _add_source(self, node_from, node_from_dim, node_to, node_to_dim, init=False):
        node_from_dim = self._transform_index(node_from, node_from_dim)
        node_from_trace = self._find_trace_from_node(node_from)
        node_to_dim = self._transform_index(node_to, node_to_dim)
        node_to_trace = self._find_trace_from_node(node_to)
        node_from_idx = _find_idx_by_name(node_from.name, self.node_list)
        if init:
            node_to_trace["source"][node_to_dim] = {}
        # add dim to cur new source
        if node_from_idx not in node_to_trace["source"][node_to_dim]:
            node_to_trace["source"][node_to_dim][node_from_idx] = [node_from_dim]
        else:
            if node_from_dim not in node_to_trace["source"][node_to_dim][node_from_idx]:
                node_to_trace["source"][node_to_dim][node_from_idx].append(
                    node_from_dim
                )
        # update inputs source
        node_to_trace["source"][node_to_dim].update(
            node_from_trace["source"][node_from_dim]
        )

    def _mark_computation_from_node(self, node_from, node_to, exclude=None):
        if exclude == None:
            exclude = []
        else:
            exclude = [self._transform_index(node_to, i) for i in exclude]
        node_from_compute = self._find_compute_trace_from_node(node_from)
        node_to_compute = self._find_compute_trace_from_node(node_to)
        # assert len(node_from_compute) == len(node_to_compute)
        for i in range(-1, -min(len(node_from_compute), len(node_to_compute)) - 1, -1):
            if self._transform_index(node_to, i) in exclude:
                continue
            self._add_source(node_from, i, node_to, i)
            for j in node_from_compute[i]:
                if j not in node_to_compute[i]:
                    node_to_compute[i].append(j)

    def _mark_idx_equal(self, node1, dim1, node2, dim2):
        """
        Mark 2 index to be equal.

        Args:
            idx1 (int): index count.
            idx2 (int): index count.
        """
        # node1_idx = _find_idx_by_name(node1.name, self.nodes_list)
        # node2_idx = _find_idx_by_name(node2.name, self.nodes_list)
        # if node1_idx > node2_idx:
        #     self._add_source(node2, dim2, node1, dim1)
        # else:
        #     self._add_source(node1, dim1, node2, dim2)

    def _mark_computation(self, node, idx, dim):
        """
        Mark some dims of node as computed.

        Args:
            node (node)
            idx (int): node index
            dim (list or int): dims to be marked as computed
        """
        if isinstance(dim, int):
            dim = [dim]
        dims = list(range(len(_get_node_shape(node))))
        for d in dim:
            cur_dim = dims[d]
            if idx not in self.idx_trace_list[idx]["compute"][cur_dim]:
                self.idx_trace_list[idx]["compute"][cur_dim].append(idx)

    def _find_trace_from_node(self, node):
        """
        Find node idx and compute trace by the node.

        Args:
            node (node)
        Returns:
            idx (list): idx of the node
            compute (list): computed idx of the node.
        """
        node_idx = _find_idx_by_name(node.name, self.node_list)
        node_dict = self.idx_trace_list[node_idx]
        return node_dict

    def _find_source_trace_from_node(self, node):
        """
        Find node source trace by the node.

        Args:
            node (node)
        Returns:
            idx (list): idx of the node
            compute (list): computed idx of the node.
        """
        node_idx = _find_idx_by_name(node.name, self.node_list)
        node_dict = self.idx_trace_list[node_idx]
        return node_dict["source"]

    def _find_idx_trace_from_node(self, node):
        """
        Find node idx trace by the node.

        Args:
            node (node)
        Returns:
            idx (list): idx of the node
        """
        node_idx = _find_idx_by_name(node.name, self.node_list)
        return self.idx_trace_list[node_idx]["idx"]

    def _find_compute_trace_from_node(self, node):
        """
        Find node compute trace by the node.

        Args:
            node (node)
        Returns:
            compute (list): computed idx of the node.
        """
        node_idx = _find_idx_by_name(node.name, self.node_list)
        return self.idx_trace_list[node_idx]["compute"]

    def _assign_index_as_input(self, node, node_idx, input_node=None):
        """
        Assign node's trace as its input node.

        Args:
            node (node)
            node_idx (int)
        """
        if input_node == None:
            input_node = node.args[0]
        input_node_idx = _find_idx_by_name(input_node.name, self.node_list)
        input_node_idx_trace = self.idx_trace_list[input_node_idx]["idx"]

        new_idx_trace = copy.deepcopy(input_node_idx_trace)
        self.idx_trace_list[node_idx]["idx"] = new_idx_trace

        self._inherit_all_computation(input_node, node)

    def _assign_all_index(self, node, node_idx):
        """
        Add new index for all node's dims.

        Args:
            node (node)
            node_idx (int)
        """
        shape = node.meta["tensor_meta"].shape
        new_trace = []
        for _ in shape:
            new_trace.append(self._add_index())
        self.idx_trace_list[node_idx]["idx"] = new_trace

    def _assign_transpose_index(self, node, node_idx):
        """
        Assign index for transpose op.
        1. swap input's dim according to transpose args
        2. inherit input's computation

        Args:
            node (node)
            node_idx (int)
        """
        input_node = node.args[0]
        tranpose_dim = node.args[1:]

        self._assign_index_as_input(node, node_idx, input_node)
        self._inherit_index(input_node, tranpose_dim[1], node, tranpose_dim[0])
        self._inherit_index(input_node, tranpose_dim[0], node, tranpose_dim[1])

    def _assign_permute_index(self, node, node_idx):
        """
        Assign index for permute op.
        1. swap input's dim according to permute args
        2. inherit input's computation

        Args:
            node (node)
            node_idx (int)
        """
        permute_dim = node.args[1:]
        input_node = node.args[0]

        self._assign_index_as_input(node, node_idx, input_node)
        for idx, d in enumerate(permute_dim):
            self._inherit_index(input_node, d, node, idx)

    def _assign_linear_index(self, node, node_idx):
        """
        Assign index for linear op.
        1. copy trace from input node and change last index accroding to weight
        2. mark equal for input node last index, weight first dim and bias dim.
        3. inherit input's computation, mark computation for last dim.

        Args:
            node (node)
            node_idx (int)
        """
        if len(node.args) == 2:
            input_node, weight = node.args
            bias = None
        else:
            input_node, weight, bias = node.args

        self._assign_index_as_input(node, node_idx)
        self._inherit_index(weight, 1, node, -1)

        self._mark_computation(node, node_idx, [-1])
        self._mark_idx_equal(input_node, -1, weight, 0)

        if bias:
            self._mark_idx_equal(input_node, -1, bias, 0)

    def _assign_matmul_index(self, node, node_idx):
        """
        Assign index for matmul op.
        1. copy trace from matmul_left and change last index accroding to matmul_right. (assert they have same length)
        2. mark equal for input matmul_left -1 index and matmul_right -2 dim.
        3. inherit matmul_left and matmul_right computation, mark computation for last dim.

        Args:
            node (node)
            node_idx (int)
        """
        matmul_left, matmul_right = node.args

        assert len(_get_node_shape(matmul_left)) == len(_get_node_shape(matmul_right))
        self._assign_index_as_input(node, node_idx, matmul_left)
        self._inherit_index(matmul_right, -1, node, -1)

        self._mark_computation_from_node(matmul_right, node, [-1, -2])
        self._mark_computation(node, node_idx, [-1])
        self._mark_idx_equal(matmul_left, -1, matmul_right, -2)

    def _assign_layernorm_index(self, node, idx):
        """
        Assign index for layernorm op.
        1. assign index as input node
        2. inherit computation and mark last 2 dims as computed.

        Args:
            node (node)
            node_idx (int)
        """
        self._assign_index_as_input(node, idx)
        self._mark_computation(node, idx, [-1])

    def _assign_elementwise_index(self, node, idx):
        """
        Assign index for element-wise op (eg. relu sigmoid add mul).
        1. assign index as input node
        2. inherit computation from all input nodes.

        Args:
            node (node)
            node_idx (int)
        """
        self._assign_index_as_input(node, idx)
        nodes_in = []
        for node_in in node.args:
            if type(node_in) == type(node):
                nodes_in.append(node_in)
                self._mark_computation_from_node(node_in, node)
        assert len(nodes_in) <= 2
        if len(nodes_in) == 2:
            node_in0_shape = _get_node_shape(nodes_in[0])
            node_in1_shape = _get_node_shape(nodes_in[1])
            for i in range(-1, -min(len(node_in0_shape), len(node_in1_shape)) - 1, -1):
                if node_in0_shape[i] == node_in1_shape[i]:
                    self._mark_idx_equal(nodes_in[0], i, nodes_in[1], i)

    def _assgin_no_change_index(self, node, idx):
        self._assign_index_as_input(node, idx)
        for node_in in node.args:
            if type(node_in) == type(node):
                self._mark_computation_from_node(node_in, node)

    def _assign_einsum_index(self, node, idx):
        """
        Assign index for einsum op.

        Args:
            node (node)
            node_idx (int)
        """
        patterns = node.args[0]
        input_nodes = node.args[1:]

        patterns = patterns.replace(" ", "")
        left, right = patterns.split("->")
        left = left.split(",")

        all_index = []
        for i in left:
            for c in i:
                all_index.append(c)
        all_index = set(all_index)
        free_index = set([i for i in right])
        sum_index = all_index - free_index

        for right_idx, right_indice in enumerate(right):
            for left_idx, left_str in enumerate(left):
                if right_indice in left_str:
                    source_idx = left_str.index(right_indice)
                    self._inherit_index(
                        input_nodes[left_idx], source_idx, node, right_idx
                    )

        # for i in sum_index:
        #     for left_idx, left_str in enumerate(left):
        #         if i in left_str:
        #             self._mark_computation(node, idx, left_str.index(i))
        #             break

    def _assign_softmax_index(self, node, idx):
        """
        Assign index for softmax op.
        1. assign index as input node
        2. inherit computation and mark softmax dim as computed.

        Args:
            node (node)
            node_idx (int)
        """
        self._assign_index_as_input(node, idx)
        self._mark_computation(node, idx, [node.kwargs["dim"]])

    def _assign_unsqueeze_index(self, node, node_idx):
        """
        Assign index for unsqueeze op.
        1. assign new index for unsqueeze dim

        Args:
            node (node)
            node_idx (int)
        """
        self._del_dim(node_idx, -1)
        self._assign_index_as_input(node, node_idx)
        self._add_dim(node_idx, node.args[1])

    def _assign_dropout_index(self, node, node_idx):
        """
        Assign index for unsqueeze op.
        1. assign new index for unsqueeze dim

        Args:
            node (node)
            node_idx (int)
        """
        self._assign_index_as_input(node, node_idx)

    def _assign_ones_like_index(self, node, node_idx):
        """
        Assign index for oneslike op.
        1. assign new index for all dim

        Args:
            node (node)
            node_idx (int)
        """
        self._assign_all_index(node, node_idx)

    def _assign_view_reshape_index(self, node, node_idx):
        """
        Assign index for view and reshape op.
        1. get origin shape and target shape by meta info.
        2. compute the real value of -1 in target shape.
        3. determine changed dim, and assgin index for generated dim.
        4. log changed dim and generated dim for restore
        5. inherit computation.
        6. TODO: look into view list to see whether the view is associated with other,
           if so assgin equal dim according to previous view.

        Args:
            node (node)
            node_idx (int)
        """
        # get data, turn into number
        origin_node = node.args[0]
        origin_shape = origin_node.meta["tensor_meta"].shape
        target_shape = []
        for i in range(1, len(node.args)):
            if isinstance(node.args[i], int):
                target_shape.append(node.args[i])
            else:
                target_shape.append(node.args[i].meta["fwd_out"][0])

        # compute the value of -1
        if -1 in target_shape:
            origin_product = 1
            for i in origin_shape:
                origin_product *= i
            target_product = -1
            for i in target_shape:
                target_product *= i
            shape_idx = target_shape.index(-1)
            target_shape[shape_idx] = origin_product // target_product

        # determine changed dim
        len_diff = len(origin_shape) - len(target_shape)
        if len_diff == 1:
            # dim merge
            dim_equal = [i == j for i, j in zip(origin_shape[:-1], target_shape)]
            dim_to = [dim_equal.index(False)]
            dim_from = [dim_equal.index(False), dim_equal.index(False) + 1]
            self._add_dim(node_idx, -1)
        elif len_diff == -1:
            # dim expand
            dim_equal = [i == j for i, j in zip(origin_shape, target_shape[:-1])]
            dim_from = [dim_equal.index(False)]
            dim_to = [dim_equal.index(False), dim_equal.index(False) + 1]
            self._del_dim(node_idx, -1)
        else:
            raise NotImplementedError(
                "shape"
                + str(origin_shape)
                + "and"
                + str(target_shape)
                + "view not implemented"
            )

        # get new index
        origin_trace = self._find_idx_trace_from_node(origin_node)
        self._assign_index_as_input(node, node_idx, origin_node)
        dim_from.reverse()
        for i in dim_from:
            self._del_dim(node_idx, i)
        for i in dim_to:
            self._add_dim(node_idx, i)

        # inherit computation
        compute_log = self._find_compute_trace_from_node(origin_node)
        for i in dim_from:
            if origin_trace[i] in compute_log:
                for j in dim_to:
                    self._mark_computation(node, node_idx, [j])
                break

        # log view, not used now
        view_dict = {
            "idx_from": [origin_trace[i] for i in dim_from],
            "dim_from": dim_from,
            "idx_to": [self.idx_trace_list[node_idx]["idx"][i] for i in dim_to],
            "dim_to": dim_to,
        }
        self.idx_view_list[node] = view_dict

    def _merge_equal_idx(self):
        idx_equal = copy.deepcopy(self.idx_trace_equal)
        idx_equal.reverse()
        for idx in idx_equal:
            merge_to = min(idx)
            merge_from = max(idx)
            for trace in self.idx_trace_list:
                if merge_from in trace["idx"]:
                    trace["idx"] = [
                        merge_to if i == merge_from else i for i in trace["idx"]
                    ]

    def trace_index(self):
        for idx, node in enumerate(self.node_list):
            if node.op == "placeholder":
                self._assign_all_index(node, idx)
            elif node.op == "call_method":
                if "transpose" in node.name:
                    self._assign_transpose_index(node, idx)
                elif "permute" in node.name:
                    self._assign_permute_index(node, idx)
                elif "view" in node.name or "reshape" in node.name:
                    self._assign_view_reshape_index(node, idx)
                elif "unsqueeze" in node.name:
                    self._assign_unsqueeze_index(node, idx)
                elif any(i in node.name for i in ["to", "contiguous"]):
                    self._assgin_no_change_index(node, idx)
                else:
                    raise NotImplementedError(node.name, "method not implemented yet!")
            elif node.op == "call_function":
                if "linear" in node.name:
                    self._assign_linear_index(node, idx)
                elif "matmul" in node.name:
                    self._assign_matmul_index(node, idx)
                elif "softmax" in node.name:
                    self._assign_softmax_index(node, idx)
                elif any(n in node.name for n in ["mul", "add", "sigmoid", "relu"]):
                    self._assign_elementwise_index(node, idx)
                elif "ones_like" in node.name:
                    self._assign_ones_like_index(node, idx)
                elif "dropout" in node.name:
                    self._assign_dropout_index(node, idx)
                elif "einsum" in node.name:
                    self._assign_einsum_index(node, idx)
                elif "getattr" in node.name:
                    continue  # get attr like shape
                elif "getitem" in node.name:
                    continue  # get item in list
                else:
                    raise NotImplementedError(
                        node.name, "function not implemented yet!"
                    )
            elif node.op == "call_module":
                if any(n in node.name for n in ["layernorm", "norm"]):
                    self._assign_layernorm_index(node, idx)
                else:
                    raise NotImplementedError(node.name, "module not implemented yet!")
            elif node.op == "get_attr":
                self._assign_all_index(node, idx)  # get param
            elif node.op == "output":
                continue
            else:
                raise NotImplementedError(node.op, "op not implemented yet!")
        # self._merge_equal_idx()

    def check_index_source(self, start_dim, start_node, start_idx, end_dim, end_node):
        """
        Check 2 given index: one index should be source of the other
        Args:
            start_idx(int): start node chunk dim
            start_node(node): start node
            end_idx(int): end node chunk dim
            end_node(node): end node

        Returns:
            bool: True if check pass
        """
        start_node_idx = _find_idx_by_name(start_node.name, self.node_list)
        end_node_trace = self._find_trace_from_node(end_node)
        end_node_trace_source = end_node_trace["source"][end_dim]
        sorted_source = sorted(
            end_node_trace_source.items(), key=lambda d: d[0], reverse=True
        )
        for node_idx, node_dim in sorted_source:
            if node_idx == start_node_idx and start_dim in node_dim:
                return True
            # it means we meet a node outside the loop, and the node is not input node
            if node_idx < start_idx:
                return False
        return False

    def check_index_compute(self, start_idx, end_dim, end_node, end_idx):
        """
        Check 2 given index: check they haven't been computed in the source trace.
        Args:
            start_idx(int): start node chunk dim
            start_node(node): start node
            end_idx(int): end node chunk dim
            end_node(node): end node

        Returns:
            bool: True if check pass
        """
        end_node_trace = self._find_trace_from_node(end_node)
        end_node_compute = end_node_trace["compute"][end_dim]
        if any(start_idx <= i <= end_idx for i in end_node_compute):
            return False
        return True

    def get_node_chunk_dim(self, node_from, node_from_dim, node_to):
        node_from_source = self._find_source_trace_from_node(node_from)
        dim_source = node_from_source[node_from_dim]
        node_to_idx = _find_idx_by_name(node_to.name, self.node_list)
        for k, v in dim_source.items():
            if k == node_to_idx:
                return v
        return None

    def _find_inherit_dim(self, input_node, input_dim, node):
        input_node_idx = _find_idx_by_name(input_node.name, self.node_list)
        node_trace_source = self._find_source_trace_from_node(node)
        for node_dim in range(len(_get_node_shape(node))):
            if (
                input_node_idx in node_trace_source[node_dim]
                and input_dim[0] in node_trace_source[node_dim][input_node_idx]
            ):
                return node_dim
        return None

    def check_index_duplicate(self, chunk_infos, return_dim=False):
        input_dim_after_node = {}
        for input_node_idx, input_node in enumerate(chunk_infos["inputs"]):
            for k, v in chunk_infos["inputs_dim"][input_node_idx].items():
                inherit_dim = self._find_inherit_dim(input_node, v, self.node_list[k])
                if inherit_dim:
                    input_dim_after_node[k] = inherit_dim

        for node in self.node_list[
            chunk_infos["region"][0] : chunk_infos["region"][1] + 1
        ]:
            if _is_non_compute_node_except_placeholder(node):
                continue
            count = 0
            duplicate_dims = []
            node_trace_source = self._find_source_trace_from_node(node)
            for node_dim in range(len(_get_node_shape(node))):
                duplicate_dim = []
                duplicate_flag = False
                dim_source = node_trace_source[node_dim]
                for k, v in dim_source.items():
                    if chunk_infos["region"][0] <= k <= chunk_infos["region"][1]:
                        if k in input_dim_after_node and input_dim_after_node[k] in v:
                            duplicate_flag = True
                            duplicate_dim.append((k, v))
                duplicate_dims.append(duplicate_dim)
                if duplicate_flag:
                    count += 1

            if count > 1:
                if return_dim:
                    return False, duplicate_dims
                else:
                    return False
        if return_dim:
            return True, None
        else:
            return True

    def _assgin_single_node_flow(
        self,
        arg_node,
        start_idx,
        end_idx,
        cur_node_dim,
        cur_node_compute,
        cur_node_source,
        cur_node_fix_dim,
        all_node_info,
        next_node_list,
    ):
        arg_idx = _find_idx_by_name(arg_node.name, self.node_list)
        # arg in chunk range or be inputs
        if not (start_idx <= arg_idx < end_idx):
            return True

        # find arg dim
        if cur_node_dim is not None:
            # dim is computed
            if arg_idx in cur_node_compute[cur_node_dim]:
                return False
            if arg_idx not in cur_node_source[cur_node_dim]:
                arg_dim = None
            else:
                arg_dim = cur_node_source[cur_node_dim][arg_idx][0]
        else:
            arg_dim = None

        # get fix dim
        arg_fix_dim = []
        if cur_node_dim is not None:
            for i in cur_node_fix_dim:
                fix_dim_source = cur_node_source[i]
                if arg_idx in fix_dim_source:
                    arg_fix_dim.append(fix_dim_source[arg_idx][0])

        # if already in node_info, arg dim must be same
        if arg_node in all_node_info:
            if all_node_info[arg_node]["chunk_dim"] != arg_dim:
                return False
            all_node_info[arg_node]["fix_dim"] = list(
                set(all_node_info[arg_node]["fix_dim"] + arg_fix_dim)
            )
        # else add it to list
        else:
            all_node_info[arg_node] = {"chunk_dim": arg_dim, "fix_dim": arg_fix_dim}

        next_node_list.append(arg_node)
        return True

    def flow_search(self, start_idx, start_dim, end_idx, end_dim):
        inputs, outputs = _find_chunk_compute_input_and_output_nodes(
            self.node_list[start_idx : end_idx + 1]
        )
        # only single ouput
        if len(outputs) > 1:
            return None

        cur_node_list = [self.node_list[end_idx]]  # start from the last node
        all_node_info = {cur_node_list[0]: {"chunk_dim": end_dim, "fix_dim": []}}

        while len(cur_node_list) > 0:
            next_node_list = []

            for cur_node in cur_node_list:
                # get cur node info
                cur_node_chunk_dim = all_node_info[cur_node]["chunk_dim"]
                cur_node_fix_dim = all_node_info[cur_node]["fix_dim"]
                cur_node_idx = _find_idx_by_name(cur_node.name, self.node_list)
                if cur_node_chunk_dim:
                    cur_node_compute = self._find_compute_trace_from_node(cur_node)
                    cur_node_source = self._find_source_trace_from_node(cur_node)
                else:
                    cur_node_compute = cur_node_source = None

                # get all valid args
                arg_list = []
                for arg in cur_node.args:
                    if type(arg) != type(cur_node):
                        continue
                    if _is_non_compute_node(arg):
                        continue
                    arg_list.append(arg)
                    flow_flag = self._assgin_single_node_flow(
                        arg,
                        start_idx,
                        end_idx,
                        cur_node_chunk_dim,
                        cur_node_compute,
                        cur_node_source,
                        cur_node_fix_dim,
                        all_node_info,
                        next_node_list,
                    )
                    if flow_flag == False:
                        return None

                if len(arg_list) == 2:
                    if any(i in cur_node.name for i in ["add", "mul"]):
                        for arg in arg_list:
                            if not (
                                start_idx
                                <= _find_idx_by_name(arg.name, self.node_list)
                                < end_idx
                            ):
                                continue
                            arg_chunk_dim = all_node_info[arg]["chunk_dim"]
                            arg_fix_dim = all_node_info[arg]["fix_dim"]
                            arg_shape = _get_node_shape(arg)
                            # add all dim as fix dim except chunk dim
                            for i, shape in enumerate(arg_shape):
                                if shape != 1 and i != cur_node_chunk_dim:
                                    if i == arg_chunk_dim:
                                        return None
                                    if i not in arg_fix_dim:
                                        arg_fix_dim.append(i)
                    elif "einsum" in cur_node.name:
                        pass
                    elif "matmul" in cur_node.name:
                        pass
                    else:
                        raise NotImplementedError()
            cur_node_list = next_node_list

        inputs_dim = []
        remove_inputs = []
        for input_node in inputs:
            input_dict = {}
            input_node_idx = _find_idx_by_name(input_node.name, self.node_list)
            for user in input_node.users.keys():
                if _is_non_compute_node(user):
                    continue
                user_idx = _find_idx_by_name(user.name, self.node_list)
                if start_idx <= user_idx <= end_idx:
                    chunk_dim = all_node_info[user]["chunk_dim"]
                    if chunk_dim is not None:
                        user_source = self._find_source_trace_from_node(user)[chunk_dim]
                        if input_node_idx in user_source:
                            input_dict[user_idx] = user_source[input_node_idx]
                        else:
                            return None
            if len(input_dict) == 0:
                remove_inputs.append(input_node)
            else:
                inputs_dim.append(input_dict)
        for i in remove_inputs:
            if i in inputs:
                inputs.remove(i)

        chunk_info = {
            "region": (start_idx, end_idx),
            "inputs": inputs,
            "inputs_non_chunk": [],
            "inputs_dim": inputs_dim,
            "outputs": outputs,
            "outputs_dim": end_dim,
            "node_chunk_dim": all_node_info,
            "args": {},
        }

        # move useless nodes ahead of loop
        # get all possible prepose nodes
        maybe_prepose_nodes = []
        for node, node_info in all_node_info.items():
            if node_info["chunk_dim"] is None:
                maybe_prepose_nodes.append(node)
        maybe_prepose_nodes.sort(
            key=lambda x: _find_idx_by_name(x.name, self.node_list),
            reverse=True,
        )  # from last node to first node
        prepose_nodes = []
        # set every node as root, search its args, if all legal, turn root and args as prepose nodes
        while len(maybe_prepose_nodes) > 0:
            tmp_cur_prepose_nodes = [maybe_prepose_nodes[0]]
            tmp_cur_related_prepose_nodes = []
            prepose_flag = True

            # loop cur node's all arg until out of chunk
            while len(tmp_cur_prepose_nodes) > 0:
                if prepose_flag == False:
                    break
                tmp_next_prepose_nodes = []
                tmp_cur_related_prepose_nodes.extend(tmp_cur_prepose_nodes)
                for cur_prepose_node in tmp_cur_prepose_nodes:
                    if prepose_flag == False:
                        break
                    for cur_prepose_node_arg in cur_prepose_node.args:
                        if type(cur_prepose_node_arg) != type(cur_prepose_node):
                            continue
                        # out of loop
                        if not (
                            start_idx
                            <= _find_idx_by_name(
                                cur_prepose_node_arg.name, self.node_list
                            )
                            < end_idx
                        ):
                            continue
                        # compute op in loop
                        elif cur_prepose_node_arg in all_node_info:
                            if all_node_info[cur_prepose_node_arg]["chunk_dim"] is None:
                                tmp_next_prepose_nodes.append(cur_prepose_node_arg)
                            else:
                                prepose_flag = False
                                break
                        # non compute op
                        else:
                            tmp_next_prepose_nodes.append(cur_prepose_node_arg)
                tmp_cur_prepose_nodes = tmp_next_prepose_nodes

            if prepose_flag == False:
                maybe_prepose_nodes.remove(maybe_prepose_nodes[0])
                continue
            else:
                for n in tmp_cur_related_prepose_nodes:
                    if n not in prepose_nodes:
                        prepose_nodes.append(n)
                    if n in maybe_prepose_nodes:
                        maybe_prepose_nodes.remove(n)
        # sort by index
        prepose_nodes.sort(key=lambda x: _find_idx_by_name(x.name, self.node_list))
        chunk_info["args"]["prepose_nodes"] = prepose_nodes

        # we need to log input nodes to avoid deleteing them in the loop
        chunk_node_list = self.node_list[start_idx : end_idx + 1]
        # also need to get some prepose node's arg out of non_chunk_inputs
        for n in prepose_nodes:
            chunk_node_list.remove(n)
        non_chunk_inputs = _find_chunk_all_input_nodes(chunk_node_list)
        for i in non_chunk_inputs:
            if i not in chunk_info["inputs"]:
                chunk_info["inputs_non_chunk"].append(i)

        # reassgin reshape size, some size may have changed due to chunk
        chunk_info = self._reassgin_reshape_size(chunk_info)

        return chunk_info

    def _reassgin_reshape_size(self, chunk_info):
        chunk_region = chunk_info["region"]
        reshape_size = {}
        chunk_shape = _get_node_shape(chunk_info["outputs"][0])[chunk_info["outputs_dim"]]
        for node in self.node_list[chunk_region[0] : chunk_region[1] + 1]:
            if any(i in node.name for i in ["reshape", "view"]):
                reshape_args = node.args[1:]
                reshape_log = self.idx_view_list[node]
                chunk_dim = chunk_info["node_chunk_dim"][node]["chunk_dim"]
                reshape_size[node.name] = {}
                for reshape_arg_dim, reshape_arg in enumerate(reshape_args):
                    if reshape_arg_dim in reshape_log["dim_to"]:
                        continue
                    if reshape_arg_dim == chunk_dim:
                        reshape_size[node.name][reshape_arg.name] = "min(chunk_size, %d - chunk_idx)" % chunk_shape
        chunk_info["reshape_size"] = reshape_size
        return chunk_info

    def _get_reorder_map(self, chunk_info):
        reorder_map = {i: i for i in range(len(self.node_list))}

        chunk_region_start = chunk_info["region"][0]
        chunk_region_end = chunk_info["region"][1]
        chunk_prepose_nodes = chunk_info["args"]["prepose_nodes"]
        chunk_prepose_nodes_idx = [
            _find_idx_by_name(i.name, self.node_list) for i in chunk_prepose_nodes
        ]
        # put prepose nodes ahead
        for idx, n in enumerate(chunk_prepose_nodes):
            n_idx = chunk_prepose_nodes_idx[idx]
            reorder_map[n_idx] = chunk_region_start + idx
        # put other nodes after prepose nodes
        for n in self.node_list[chunk_region_start : chunk_region_end + 1]:
            if n in chunk_prepose_nodes:
                continue
            n_idx = _find_idx_by_name(n.name, self.node_list)
            pos = sum([n_idx < i for i in chunk_prepose_nodes_idx])
            reorder_map[n_idx] = n_idx + pos

        return reorder_map

    def _reorder_chunk_info(self, chunk_info, reorder_map):
        # update chunk info
        chunk_info["region"] = (
            chunk_info["region"][0] + len(chunk_info["args"]["prepose_nodes"]),
            chunk_info["region"][1],
        )
        for idx, input_dim in enumerate(chunk_info["inputs_dim"]):
            new_input_dim = {}
            for k, v in input_dim.items():
                new_input_dim[reorder_map[k]] = v
            chunk_info["inputs_dim"][idx] = new_input_dim
        return chunk_info

    def _update_all_reorder_map(self, reorder_map):
        for origin_idx, map_idx in self.all_reorder_map.items():
            self.all_reorder_map[origin_idx] = reorder_map[map_idx]

    def _reorder_self_node_list(self, reorder_map):
        new_node_list = [None for _ in range(len(self.node_list))]
        for old_idx, new_idx in reorder_map.items():
            new_node_list[new_idx] = self.node_list[old_idx]
        self.node_list = new_node_list

    def _reorder_idx_trace(self, reorder_map):
        # reorder list
        new_idx_trace_list = [None for _ in range(len(self.idx_trace_list))]
        for old_idx, new_idx in reorder_map.items():
            new_idx_trace_list[new_idx] = self.idx_trace_list[old_idx]
        self.idx_trace_list = new_idx_trace_list
        # update compute
        for idx_trace in self.idx_trace_list:
            compute = idx_trace["compute"]
            for dim_compute in compute:
                for idx, i in enumerate(dim_compute):
                    dim_compute[idx] = reorder_map[i]
        # update source
        for idx_trace in self.idx_trace_list:
            source = idx_trace["source"]
            for dim_idx, dim_source in enumerate(source):
                new_dim_source = {}
                for k, v in dim_source.items():
                    new_dim_source[reorder_map[k]] = v
                source[dim_idx] = new_dim_source

    def reorder_all(self, chunk_info):
        if chunk_info is None:
            return chunk_info
        if len(chunk_info["args"]["prepose_nodes"]) == 0:
            return chunk_info
        reorder_map = self._get_reorder_map(chunk_info)
        self._update_all_reorder_map(reorder_map)
        self._reorder_idx_trace(reorder_map)
        self._reorder_self_node_list(reorder_map)
        chunk_info = self._reorder_chunk_info(chunk_info, reorder_map)
        return chunk_info

    def reorder_node_list(self, node_list):
        new_node_list = [None for _ in range(len(node_list))]
        for old_idx, new_idx in self.all_reorder_map.items():
            new_node_list[new_idx] = node_list[old_idx]
        return new_node_list


class MemoryEstimator(object):
    def __init__(self, index_tracer: IndexTracer) -> None:
        self.index_tracer = index_tracer

    def _get_meta_node_size(self, x):
        x = x.meta["tensor_meta"]
        x = x.numel * torch.tensor([], dtype=x.dtype).element_size()
        return x

    def _get_output_node(self, n):
        fwd_out = {
            x.uuid: x
            for x in n.meta["fwd_out"]
            if isinstance(x, torch.Tensor) and hasattr(x, "uuid")
        }
        out_size = activation_size(fwd_out)
        out_node = [n.name] if out_size > 0 else []
        # if any(i in n.name for i in ['transpose', 'permute', 'view']):
        #     out_size = 0
        return out_size, out_node

    def _get_output_node_size(self, n):
        return self._get_output_node(n)[0]

    def _add_active_node(self, n, active_list):
        new_active = self._get_output_node(n)[1]
        if n.op == "placeholder":
            new_active.append(n.name)
        for i in new_active:
            if i not in active_list:
                active_list.append(i)

    def _get_delete_node(self, user, user_to_last_uses, to_keep=None):
        delete_size = 0
        delete_node = []
        if user.op not in ("output",):
            nodes_to_delete = user_to_last_uses.get(user, [])
            if to_keep is not None:
                keep_list = []
                for n in nodes_to_delete:
                    if n.name in to_keep:
                        keep_list.append(n)
                for n in keep_list:
                    if n in nodes_to_delete:
                        nodes_to_delete.remove(n)
            if len(nodes_to_delete):
                out_node = [self._get_output_node(i) for i in nodes_to_delete]
                delete_size = sum([i[0] for i in out_node])
                for i in range(len(out_node)):
                    if out_node[i][0] > 0:
                        delete_node.append(out_node[i][1][0])
                    elif nodes_to_delete[i].op == "placeholder":
                        delete_node.append(nodes_to_delete[i].name)
                    # elif any(j in nodes_to_delete[i].name for j in ['transpose', 'permute', 'view']):
                    #     delete_node.append(nodes_to_delete[i].name)
        return delete_size, delete_node

    def _get_delete_node_size(self, user, user_to_last_uses, to_keep):
        return self._get_delete_node(user, user_to_last_uses, to_keep)[0]

    def _remove_deactive_node(self, user, user_to_last_uses, active_list):
        delete_node = self._get_delete_node(user, user_to_last_uses)[1]
        for i in delete_node:
            if i in active_list:
                active_list.remove(i)

    def _get_chunk_inputs_size(
        self, chunk_inputs, chunk_inputs_non_chunk, node_list, chunk_end_idx
    ):
        nodes_to_delete = []
        for chunk_input in chunk_inputs + chunk_inputs_non_chunk:
            chunk_input_users = chunk_input.users.keys()
            chunk_input_users_idx = [
                _find_idx_by_name(i.name, node_list) for i in chunk_input_users
            ]
            if all(i <= chunk_end_idx for i in chunk_input_users_idx):
                if chunk_input not in nodes_to_delete:
                    nodes_to_delete.append(chunk_input)
        out_node = [self._get_output_node(i) for i in nodes_to_delete]
        delete_size = sum([i[0] for i in out_node])
        return delete_size

    def _get_last_usr(self, nodes):
        node_to_last_use: Dict[Node, Node] = {}
        user_to_last_uses: Dict[Node, List[Node]] = {}

        def register_last_uses(n: Node, user: Node):
            if n not in node_to_last_use:
                node_to_last_use[n] = user
                user_to_last_uses.setdefault(user, []).append(n)

        for node in reversed(nodes):
            map_arg(node.args, lambda n: register_last_uses(n, node))
            map_arg(node.kwargs, lambda n: register_last_uses(n, node))
        return user_to_last_uses

    def _get_contiguous_memory(self, node, not_contiguous_list, delete=False):
        mem = 0
        not_contiguous_ops = ["permute"]
        inherit_contiguous_ops = ["transpose", "view"]

        if node.op == "call_function" and any(
            n in node.name for n in ["matmul", "reshape"]
        ):
            for n in node.args:
                if n in not_contiguous_list:
                    # matmul won't change origin tensor, but create a tmp copy
                    mem += self._get_output_node_size(n)
        elif node.op == "call_module":
            for n in node.args:
                if n in not_contiguous_list:
                    # module will just make origin tensor to contiguous
                    if delete:
                        not_contiguous_list.remove(n)
        elif node.op == "call_method" and any(
            i in node.name for i in not_contiguous_ops
        ):
            if node not in not_contiguous_list:
                not_contiguous_list.append(node)
        return mem

    def _get_chunk_ratio(self, node, chunk_node_dim, chunk_size):
        if node not in chunk_node_dim:
            return 1.0
        node_shape = _get_node_shape(node)
        chunk_dim = chunk_node_dim[node]["chunk_dim"]
        if chunk_dim is None:
            return 1.0
        else:
            return float(chunk_size) / node_shape[chunk_dim]

    def _get_chunk_delete_node_size(
        self, user, user_to_last_uses, chunk_ratio, chunk_inputs_names
    ):
        # if any(j in user.name for j in ['transpose', 'permute', 'view']):
        #     return 0
        if user.op in ("placeholder", "output"):
            return 0
        nodes_to_delete = user_to_last_uses.get(user, [])
        delete_size = 0
        for n in nodes_to_delete:
            if n.name in chunk_inputs_names:
                continue
            delete_size += self._get_output_node_size(n) * chunk_ratio
        return delete_size

    def _print_mem_log(self, log, nodes, title=None):
        if title:
            print(title)
        for idx, (l, n) in enumerate(zip(log, nodes)):
            print("%s:%.2f \t" % (n.name, l), end="")
            if (idx + 1) % 3 == 0:
                print("")
        print("\n")

    def _print_compute_op_mem_log(self, log, nodes, title=None):
        if title:
            print(title)
        for idx, (l, n) in enumerate(zip(log, nodes)):
            if n.op in ["placeholder", "get_attr", "output"]:
                continue
            if any(i in n.name for i in ["getitem", "getattr"]):
                continue
            print("%s:%.2f \t" % (n.name, l), end="")
            if (idx + 1) % 3 == 0:
                print("")
        print("\n")

    def estimate_chunk_inference_mem(
        self,
        node_list,
        chunk_infos=None,
        print_mem=False,
    ):
        act_memory = 0.0
        act_memory_peak_log = []
        act_memory_after_node_log = []
        active_node_list = []
        active_node_list_log = []
        not_contiguous_list = []
        user_to_last_uses = self._get_last_usr(node_list)
        user_to_last_uses_no_free_var = self._get_last_usr(node_list)
        _delete_free_var_from_last_use(user_to_last_uses_no_free_var)

        use_chunk = True if chunk_infos is not None else False
        chunk_within = False
        chunk_region_idx = None
        chunk_ratio = 1  # use it to estimate chunk mem
        chunk_inputs_names = []

        if use_chunk:
            chunk_regions = [i["region"] for i in chunk_infos]
            chunk_starts = [i[0] for i in chunk_regions]
            chunk_ends = [i[1] for i in chunk_regions]
            chunk_inputs = [i["inputs"] for i in chunk_infos]
            chunk_inputs_non_chunk = [i["inputs_non_chunk"] for i in chunk_infos]
            chunk_inputs_names = [j.name for i in chunk_inputs for j in i] + [
                j.name for i in chunk_inputs_non_chunk for j in i
            ]
            chunk_outputs = [i["outputs"][0] for i in chunk_infos]
            chunk_node_dim = [i["node_chunk_dim"] for i in chunk_infos]
            chunk_sizes = [
                i["chunk_size"] if "chunk_size" in i else 1 for i in chunk_infos
            ]

        for idx, node in enumerate(node_list):
            # if node in chunk start nodes, change chunk ratio and add chunk_tensor
            if use_chunk and idx in chunk_starts:
                chunk_within = True
                chunk_region_idx = chunk_starts.index(idx)
                act_memory += self._get_output_node_size(
                    chunk_outputs[chunk_region_idx]
                ) / (1024**2)

            # determine chunk ratio for current node
            if chunk_within:
                chunk_ratio = self._get_chunk_ratio(
                    node,
                    chunk_node_dim[chunk_region_idx],
                    chunk_sizes[chunk_region_idx],
                )

            # if node is placeholder, just add the size of the node
            if node.op == "placeholder":
                act_memory += self._get_meta_node_size(node) * chunk_ratio / (1024**2)
                act_memory_peak_log.append(act_memory)
            # skip output
            elif node.op == "output":
                continue
            # no change for non compute node
            elif _is_non_compute_node_except_placeholder(node):
                act_memory_peak_log.append(act_memory)
            # node is a compute op
            # calculate tmp, output node and delete node memory
            else:
                # forward memory
                # TODO: contiguous_memory still not accurate for matmul, view, reshape and transpose
                act_memory += (
                    self._get_contiguous_memory(node, not_contiguous_list)
                    * chunk_ratio
                    / (1024**2)
                )
                act_memory += (
                    self._get_output_node_size(node) * chunk_ratio / (1024**2)
                )
                # record max act memory
                act_memory_peak_log.append(act_memory)
                # delete useless memory
                act_memory -= (
                    self._get_contiguous_memory(node, not_contiguous_list, delete=True)
                    * chunk_ratio
                    / (1024**2)
                )
                # delete unused vars not in chunk_input_list
                # we can't delete input nodes until chunk ends
                if chunk_within:
                    act_memory -= self._get_chunk_delete_node_size(
                        node,
                        user_to_last_uses_no_free_var,
                        chunk_ratio,
                        chunk_inputs_names,
                    ) / (1024**2)
                else:
                    act_memory -= self._get_delete_node_size(
                        node, user_to_last_uses_no_free_var, chunk_inputs_names
                    ) / (1024**2)

            # log active node, only effective without chunk
            self._add_active_node(node, active_node_list)
            self._remove_deactive_node(node, user_to_last_uses, active_node_list)

            # if node in chunk end nodes, restore chunk settings
            if use_chunk and idx in chunk_ends:
                act_memory -= (
                    self._get_output_node_size(node) * chunk_ratio / (1024**2)
                )
                act_memory -= self._get_chunk_inputs_size(
                    chunk_inputs[chunk_region_idx],
                    chunk_inputs_non_chunk[chunk_region_idx],
                    node_list,
                    chunk_regions[chunk_region_idx][1],
                ) / (1024**2)
                chunk_within = False
                chunk_ratio = 1
                chunk_region_idx = None

            act_memory_after_node_log.append(act_memory)
            active_node_list_log.append(copy.deepcopy(active_node_list))

        if print_mem:
            print("with chunk" if use_chunk else "without chunk")
            # self._print_mem_log(act_memory_peak_log, node_list, "peak")
            # self._print_mem_log(act_memory_after_node_log, node_list, "after")
            self._print_compute_op_mem_log(act_memory_peak_log, node_list, "peak")
            self._print_compute_op_mem_log(
                act_memory_after_node_log, node_list, "after"
            )

        # param_memory = parameter_size(gm)
        # all_memory = act_memory + param_memory
        return act_memory_peak_log, act_memory_after_node_log, active_node_list_log


class ChunkSelector(object):
    def __init__(
        self, index_tracer: IndexTracer, memory_estimator: MemoryEstimator, stratge
    ):
        self.index_tracer = index_tracer
        self.memory_estimator = memory_estimator
        assert stratge in ["min_memory", "fit_memory"]
        self.stratge = stratge
        self.max_memory = 600  # MB

    def _select_best_chunk_region(
        self, possible_chunk_regions, chunk_infos, peak_node, max_chunk_region, mem_peak
    ):
        if self.stratge == "min_memory":
            best_region = self._select_min_memory_chunk_region(
                possible_chunk_regions, chunk_infos
            )
        elif self.stratge == "fit_memory":
            best_region = self._select_fit_memory_chunk_region(
                possible_chunk_regions,
                chunk_infos,
                peak_node,
                max_chunk_region,
                mem_peak,
            )
        else:
            raise RuntimeError()
        return best_region

    def _select_fit_memory_chunk_region(
        self, possible_chunk_regions, chunk_infos, peak_node, max_chunk_region, mem_peak
    ):
        # stop chunk if max memory satisfy memory limit
        if max(mem_peak) < self.max_memory:
            return None

        # remove illegal regions
        illegal_regions = []
        for i in possible_chunk_regions:
            if not self._is_legal_region(i, chunk_infos):
                illegal_regions.append(i)
        for i in illegal_regions:
            if i in possible_chunk_regions:
                possible_chunk_regions.remove(i)

        # get mem for chunk region
        regions_dict = []
        for region in possible_chunk_regions:
            cur_chunk_infos = chunk_infos + [region]
            cur_mem_peak = self.memory_estimator.estimate_chunk_inference_mem(
                self.index_tracer.node_list, cur_chunk_infos
            )[0]
            cur_chunk_region_peak = cur_mem_peak[
                max_chunk_region[0] : max_chunk_region[1] + 1
            ]
            cur_chunk_region_max_peak = max(cur_chunk_region_peak)
            if cur_chunk_region_max_peak < self.max_memory:
                regions_dict.append(
                    {
                        "chunk_info": region,
                        "chunk_max_mem": cur_chunk_region_max_peak,
                        "chunk_len": self._get_compute_node_num(
                            region["region"][0], region["region"][1]
                        ),
                    }
                )
        # no region found
        if len(regions_dict) == 0:
            return None

        # select the min chunk len
        chunk_len = [i["chunk_len"] for i in regions_dict]
        best_region_idx = chunk_len.index(min(chunk_len))
        best_region = regions_dict[best_region_idx]["chunk_info"]

        # get max chunk size
        best_region = self._get_fit_chunk_size(best_region, chunk_infos)
        return best_region

    def _get_fit_chunk_size(self, chunk_info, chunk_infos):
        chunk_size = 1
        chunk_info["chunk_size"] = chunk_size
        cur_chunk_max_mem = 0
        # search a region
        while cur_chunk_max_mem < self.max_memory:
            chunk_size *= 2
            chunk_info["chunk_size"] = chunk_size
            cur_chunk_infos = chunk_infos + [chunk_info]
            cur_mem_peak = self.memory_estimator.estimate_chunk_inference_mem(
                self.index_tracer.node_list, cur_chunk_infos
            )[0]
            cur_chunk_max_mem = max(
                cur_mem_peak[chunk_info["region"][0] : chunk_info["region"][1] + 1]
            )
        # search exact size
        chunk_info["chunk_size"] = self._chunk_size_binary_search(
            chunk_size // 2, chunk_size, chunk_info, chunk_infos
        )
        return chunk_info

    def _chunk_size_binary_search(self, l, r, chunk_info, chunk_infos):
        if l >= 16:
            gap = 4
        else:
            gap = 1
        while r >= l + gap:
            mid = int(l + (r - l)/2)
            chunk_info["chunk_size"] = mid
            cur_chunk_infos = chunk_infos + [chunk_info]
            cur_mem_peak = self.memory_estimator.estimate_chunk_inference_mem(
                self.index_tracer.node_list, cur_chunk_infos
            )[0]
            cur_chunk_max_mem = max(
                cur_mem_peak[chunk_info["region"][0] : chunk_info["region"][1] + 1]
            )
            if cur_chunk_max_mem >= self.max_memory:
                r = mid - gap
            else:
                l = mid + gap
        return l

    def _get_compute_node_num(self, start, end):
        count = 0
        for i in self.index_tracer.node_list[start : end + 1]:
            if _is_non_compute_node(i):
                count += 1
        return count

    def _select_min_memory_chunk_region(self, possible_chunk_regions, chunk_infos):
        max_region_range = 0
        best_region = None
        while len(possible_chunk_regions) > 0:
            for i in possible_chunk_regions:
                if i["region"][1] - i["region"][0] > max_region_range:
                    best_region = i
                    max_region_range = i["region"][1] - i["region"][0]
            if self._is_legal_region(best_region, chunk_infos):
                break
            possible_chunk_regions.remove(i)
            max_region_range = 0
            best_region = None
        return best_region

    def _is_legal_region(self, cur_chunk_info, chunk_infos):
        (chunk_region_start, chunk_region_end) = cur_chunk_info["region"]
        if cur_chunk_info in chunk_infos:
            return False
        if chunk_region_end < chunk_region_start:
            return False
        for i in chunk_infos:
            region = i["region"]
            if not (
                (chunk_region_start > region[1] and chunk_region_end > region[1])
                or (chunk_region_start < region[0] and chunk_region_end < region[0])
            ):
                return False
        return True


class ChunkRegionSearch(object):
    def __init__(self, gm) -> None:
        self.gm = gm
        self.index_tracer = IndexTracer(list(gm.graph.nodes))
        self.index_tracer.trace_index()
        self.memory_estimator = MemoryEstimator(self.index_tracer)
        self.chunk_selector = ChunkSelector(
            self.index_tracer, self.memory_estimator, stratge="fit_memory"
        )

    def _find_peak_node(self, mem_peak):
        max_value = max(mem_peak)
        max_idx = mem_peak.index(max_value)
        return max_idx

    def _get_free_var(self):
        free_var_idx = []
        for idx, n in enumerate(self.index_tracer.node_list):
            if n.op == "placeholder":
                free_var_idx.append(idx)
        return free_var_idx

    def _get_min_free_var(self, active_node_list, free_vars):
        min_len = 999
        for idx, n in enumerate(active_node_list):
            if idx in free_vars:
                continue
            if len(n) < min_len:
                min_len = len(n)
        return min_len

    def _search_max_chunk_region(self, active_node, peak_node, chunk_regions):
        free_vars = self._get_free_var()
        free_var_num = len(free_vars)
        active_node_num = [len(i) for i in active_node]
        min_active_node_num = min(active_node_num[free_var_num:])
        threshold = max(free_var_num, min_active_node_num)

        # from peak_node to free_var
        inside_flag = False
        chunk_region_start = free_var_num
        for i in range(peak_node, -1, -1):
            if active_node_num[i] <= threshold:
                inside_flag = True
            if inside_flag and active_node_num[i] > threshold:
                chunk_region_start = i + 1
                break

        # from peak_node to len-2
        inside_flag = False
        chunk_region_end = len(active_node) - 1
        for i in range(peak_node, len(active_node)):
            if active_node_num[i] <= threshold:
                inside_flag = True
            if inside_flag and active_node_num[i] > threshold:
                chunk_region_end = i
                break

        for i in chunk_regions:
            region = i["region"]
            if chunk_region_start >= region[0] and chunk_region_end <= region[1]:
                return None
            elif (
                region[0] <= chunk_region_start <= region[1]
                and chunk_region_end > region[1]
            ):
                chunk_region_start = region[1] + 1
            elif (
                region[0] <= chunk_region_end <= region[1]
                and chunk_region_start < region[0]
            ):
                chunk_region_end = region[0] - 1
        return chunk_region_start, chunk_region_end

    def _is_not_compute(self, trace, chunk_range, dim_idx):
        if trace["idx"][dim_idx] not in trace["compute"]:
            return True
        if trace["idx"][dim_idx] in trace["compute"] and all(
            i < chunk_range[0] or i > chunk_range[1]
            for i in trace["compute"][trace["idx"][dim_idx]]
        ):
            return True
        return False

    def _find_free_dim(self, input_trace, output_trace, start_idx, end_idx):
        start_traces = input_trace[start_idx]
        end_trace = output_trace[end_idx]
        end_node = self.index_tracer.node_list[end_idx]
        chunk_infos = []
        for end_dim, _ in enumerate(end_trace["idx"]):
            if len(start_traces) > 1:
                continue
            for start_node, start_trace in start_traces.items():
                for start_dim, _ in enumerate(start_trace["idx"]):
                    # dim size cannot be 1
                    if (
                        _get_node_shape(end_node)[end_dim] == 1
                        or _get_node_shape(start_node)[start_dim] == 1
                    ):
                        continue
                    # check index source align
                    if not self.index_tracer.check_index_source(
                        start_dim, start_node, start_idx, end_dim, end_node
                    ):
                        continue
                    # check index copmute
                    if not self.index_tracer.check_index_compute(
                        start_idx, end_dim, end_node, end_idx
                    ):
                        continue
                    # flow search
                    chunk_info = self.index_tracer.flow_search(
                        start_idx, start_dim, end_idx, end_dim
                    )
                    if chunk_info is None:
                        continue
                    # check index copmute
                    if not self.index_tracer.check_index_duplicate(chunk_info):
                        continue
                    chunk_infos.append(chunk_info)
        return chunk_infos

    def _search_possible_chunk_regions(self, max_chunk_region, peak_node):
        possible_chunk_region = []
        output_trace = copy.deepcopy(self.index_tracer.idx_trace_list)
        input_trace = []  # trace of a node's input nodes
        for _, n in enumerate(self.index_tracer.node_list):
            cur_trace = {}
            for arg in n.args:
                if type(arg) == type(n) and not _is_non_compute_node_except_placeholder(
                    arg
                ):
                    cur_trace[arg] = self.index_tracer._find_trace_from_node(arg)
            input_trace.append(cur_trace)

        for start_idx in range(max_chunk_region[0], peak_node + 1):
            for end_idx in range(peak_node, max_chunk_region[1] + 1):
                # skip non compute nodes
                if _is_non_compute_node(
                    self.index_tracer.node_list[start_idx]
                ) or _is_non_compute_node(self.index_tracer.node_list[end_idx]):
                    continue

                # select free dim
                chunk_info = self._find_free_dim(
                    input_trace, output_trace, start_idx, end_idx
                )
                if len(chunk_info) > 0:
                    possible_chunk_region.extend(chunk_info)
        return possible_chunk_region

    def _step_search(self, mem_peak, active_node, chunk_regions):
        peak_node = self._find_peak_node(mem_peak)
        max_chunk_region = self._search_max_chunk_region(
            active_node, peak_node, chunk_regions
        )
        if max_chunk_region == None:
            return None
        possible_chunk_regions = self._search_possible_chunk_regions(
            max_chunk_region, peak_node
        )
        best_chunk_region = self.chunk_selector._select_best_chunk_region(
            possible_chunk_regions, chunk_regions, peak_node, max_chunk_region, mem_peak
        )
        best_chunk_region = self.index_tracer.reorder_all(best_chunk_region)
        return best_chunk_region

    def _stop_search(self, init_mem_peak, mem_peak):
        sorted_init_mem_peak = sorted(init_mem_peak)
        if max(mem_peak) < sorted_init_mem_peak[int(len(sorted_init_mem_peak) * 0.5)]:
            return True
        return False

    def search_region(self):
        chunk_infos = []
        (
            init_mem_peak,
            _,
            active_node,
        ) = self.memory_estimator.estimate_chunk_inference_mem(
            self.index_tracer.node_list
        )
        mem_peak = init_mem_peak

        while True:
            chunk_info = self._step_search(mem_peak, active_node, chunk_infos)
            if chunk_info is None:
                break
            chunk_infos.append(chunk_info)

            (
                mem_peak,
                _,
                active_node,
            ) = self.memory_estimator.estimate_chunk_inference_mem(
                self.index_tracer.node_list, chunk_infos, print_mem=True
            )
            if self._stop_search(init_mem_peak, mem_peak):
                break
        return chunk_infos


def _gen_chunk_slice_dim(chunk_dim, chunk_idx_name, shape):
    new_shape = "["
    for idx, i in enumerate(shape):
        if idx == chunk_dim:
            new_shape += "%s:%s + chunk_size" % (chunk_idx_name, chunk_idx_name)
        else:
            new_shape += ":"
        new_shape += ", "
    new_shape = new_shape[:-2] + "]"
    return new_shape


def _gen_loop_start(chunk_input, chunk_output, chunk_ouput_dim, chunk_size=2):
    input_node = chunk_input[0]
    out_shape = _get_node_shape(chunk_output)
    out_str = str(list(out_shape))
    context = (
        "chunk_result = torch.empty(%s, dtype=%s.dtype, device=%s.device); chunk_size = %d\nfor chunk_idx in range"
        % (out_str, input_node.name, input_node.name, chunk_size)
    )
    context += "(0, %d, chunk_size):\n" % (out_shape[chunk_ouput_dim])
    return context


def _gen_loop_end(
    chunk_inputs, chunk_non_compute_inputs, chunk_outputs, chunk_outputs_dim, node_list
):
    chunk_outputs_name = chunk_outputs.name
    chunk_outputs_idx = _find_idx_by_name(chunk_outputs_name, node_list)
    chunk_output_shape = chunk_outputs.meta["tensor_meta"].shape
    chunk_slice = _gen_chunk_slice_dim(
        chunk_outputs_dim, "chunk_idx", chunk_output_shape
    )
    context = "    chunk_result%s = %s;  %s = None\n" % (
        chunk_slice,
        chunk_outputs_name,
        chunk_outputs_name,
    )
    context += (
        chunk_outputs_name + " = chunk_result;  chunk_result = None;  chunk_size = None"
    )

    # determine if its the last use for chunk input
    for chunk_input in chunk_inputs + chunk_non_compute_inputs:
        if all(
            [
                _find_idx_by_name(user.name, node_list) <= chunk_outputs_idx
                for user in chunk_input.users.keys()
            ]
        ):
            context += ";  %s = None" % chunk_input.name

    context += "\n"
    return context


def _find_chunk_all_input_nodes(nodes: List[Node]):
    """
    Find non-compute input and output node names.
    input nodes are nodes used in the list
    output nodes are nodes will use nodes in the list
    """
    input_nodes = []
    for node in nodes:
        for input_node in node._input_nodes.keys():
            if input_node not in nodes and input_node not in input_nodes:
                input_nodes.append(input_node)
    return input_nodes


def _find_chunk_compute_input_and_output_nodes(nodes: List[Node]):
    """
    Find non-compute input and output node names.
    input nodes are nodes used in the list
    output nodes are nodes will use nodes in the list
    """
    input_nodes = []
    output_nodes = []

    # if a node has an input node which is not in the node list
    # we treat that input node as the input of the checkpoint function
    for node in nodes:
        for input_node in node._input_nodes.keys():
            if (
                input_node not in nodes
                and input_node not in input_nodes
                and not _is_non_compute_node_except_placeholder(input_node)
            ):
                input_nodes.append(input_node)

    # if a node has a user node which is not in the node list
    # we treat that user node as the node receiving the current node output
    for node in nodes:
        for output_node in node.users.keys():
            if (
                output_node not in nodes
                and node not in output_nodes
                and not _is_non_compute_node_except_placeholder_output(output_node)
            ):
                output_nodes.append(node)

    return input_nodes, output_nodes


def _find_idx_by_name(name, nodes_list):
    for idx, node in enumerate(nodes_list):
        if node.name == name:
            return idx
    raise RuntimeError("name %s not found in node list" % name)


def _replace_name(context, name_from, name_to):
    patterns = [(" ", " "), (" ", "."), (" ", ","), ("(", ")"), ("(", ",")]
    for p in patterns:
        source = p[0] + name_from + p[1]
        target = p[0] + name_to + p[1]
        if source in context:
            context = context.replace(source, target)
    return context


def _replace_reshape_size(context, node_name, reshape_size_dict):
    if node_name not in reshape_size_dict:
        return context
    for size_name, size_value in reshape_size_dict[node_name].items():
        context = context.replace(size_name, size_value)
    return context


def emit_code_with_chunk(
    body,
    ckpt_func,
    nodes,
    emit_node_func,
    delete_unused_value_func,
    meta_nodes,
    meta_graph,
):
    """Emit code with nested activation checkpoint
    When we detect some of the node.activation_checkpoint is a List, we will use
    this function to emit the activation checkpoint codes.

    Args:
        body: forward code
        ckpt_func: checkpoint functions code
        nodes: graph.nodes
        emit_node_func: function to emit node
        delete_unused_value_func: function to remove the unused value
    """
    node_list = list(nodes)

    # find the chunk regions
    chunk_region_search = ChunkRegionSearch(meta_graph)
    chunk_search = chunk_region_search.search_region()

    chunk_regions = [i["region"] for i in chunk_search]
    chunk_starts = [i[0] for i in chunk_regions]
    chunk_ends = [i[1] for i in chunk_regions]

    chunk_inputs = [i["inputs"] for i in chunk_search]
    chunk_inputs_non_chunk = [i["inputs_non_chunk"] for i in chunk_search]
    chunk_inputs_dim = [i["inputs_dim"] for i in chunk_search]
    chunk_inputs_names = [j.name for i in chunk_inputs for j in i] + [
        j.name for i in chunk_inputs_non_chunk for j in i
    ]

    chunk_outputs = [i["outputs"][0] for i in chunk_search]
    chunk_outputs_dim = [i["outputs_dim"] for i in chunk_search]

    node_list = chunk_region_search.index_tracer.reorder_node_list(node_list)
    node_idx = 0
    region_idx = 0
    within_chunk_region = False

    while node_idx < len(node_list):
        node = node_list[node_idx]

        if node_idx in chunk_starts:
            within_chunk_region = True
            region_idx = chunk_starts.index(node_idx)
            body.append(
                _gen_loop_start(
                    chunk_inputs[region_idx],
                    chunk_outputs[region_idx],
                    chunk_outputs_dim[region_idx],
                    chunk_size=chunk_search[region_idx]["chunk_size"]
                )
            )

        if within_chunk_region:
            emit_node_func(node, body)
            # replace input var with chunk var
            for input_node_idx, input_node in enumerate(chunk_inputs[region_idx]):
                for idx, dim in chunk_inputs_dim[region_idx][input_node_idx].items():
                    if idx == node_idx:
                        chunk_slice = _gen_chunk_slice_dim(
                            dim[0], "chunk_idx", _get_node_shape(input_node)
                        )
                        body[-1] = _replace_name(
                            body[-1], input_node.name, input_node.name + chunk_slice
                        )
            body[-1] = _replace_reshape_size(
                body[-1], node.name, chunk_search[region_idx]["reshape_size"]
            )
            body[-1] = "    " + body[-1]
            delete_unused_value_func(node, body, chunk_inputs_names)
        else:
            emit_node_func(node, body)
            if node_idx not in chunk_inputs:
                delete_unused_value_func(node, body, chunk_inputs_names)

        if node_idx in chunk_ends:
            body.append(
                _gen_loop_end(
                    chunk_inputs[region_idx],
                    chunk_inputs_non_chunk[region_idx],
                    chunk_outputs[region_idx],
                    chunk_outputs_dim[region_idx],
                    node_list,
                )
            )
            within_chunk_region = False

        node_idx += 1


if CODEGEN_AVAILABLE:

    class ChunkCodeGen(CodeGen):
        def __init__(self, meta_graph):
            super().__init__()
            self.meta_graph = meta_graph
            self.meta_node = list(meta_graph.graph.nodes)

        def _gen_python_code(
            self, nodes, root_module: str, namespace: _Namespace
        ) -> PythonCode:
            free_vars: List[str] = []
            body: List[str] = []
            globals_: Dict[str, Any] = {}
            wrapped_fns: Dict[str, None] = {}

            # Wrap string in list to pass by reference
            maybe_return_annotation: List[str] = [""]

            def add_global(name_hint: str, obj: Any):
                """Add an obj to be tracked as a global.

                We call this for names that reference objects external to the
                Graph, like functions or types.

                Returns: the global name that should be used to reference 'obj' in generated source.
                """
                if (
                    _is_from_torch(obj) and obj != torch.device
                ):  # to support registering torch.device
                    # HACK: workaround for how torch custom ops are registered. We
                    # can't import them like normal modules so they must retain their
                    # fully qualified name.
                    return _get_qualified_name(obj)

                # normalize the name hint to get a proper identifier
                global_name = namespace.create_name(name_hint, obj)

                if global_name in globals_:
                    assert globals_[global_name] is obj
                    return global_name
                globals_[global_name] = obj
                return global_name

            # set _custom_builtins here so that we needn't import colossalai in forward
            _custom_builtins["colossalai"] = _CustomBuiltin(
                "import colossalai", colossalai
            )

            # Pre-fill the globals table with registered builtins.
            for name, (_, obj) in _custom_builtins.items():
                add_global(name, obj)

            def type_repr(o: Any):
                if o == ():
                    # Empty tuple is used for empty tuple type annotation Tuple[()]
                    return "()"

                typename = _type_repr(o)

                if hasattr(o, "__origin__"):
                    # This is a generic type, e.g. typing.List[torch.Tensor]
                    origin_type = _origin_type_map.get(o.__origin__, o.__origin__)
                    origin_typename = add_global(_type_repr(origin_type), origin_type)

                    if hasattr(o, "__args__"):
                        # Assign global names for each of the inner type variables.
                        args = [type_repr(arg) for arg in o.__args__]

                        if len(args) == 0:
                            # Bare type, such as `typing.Tuple` with no subscript
                            # This code-path used in Python < 3.9
                            return origin_typename

                        return f'{origin_typename}[{",".join(args)}]'
                    else:
                        # Bare type, such as `typing.Tuple` with no subscript
                        # This code-path used in Python 3.9+
                        return origin_typename

                # Common case: this is a regular module name like 'foo.bar.baz'
                return add_global(typename, o)

            def _format_args(
                args: Tuple[Argument, ...], kwargs: Dict[str, Argument]
            ) -> str:
                def _get_repr(arg):
                    # Handle NamedTuples (if it has `_fields`) via add_global.
                    if isinstance(arg, tuple) and hasattr(arg, "_fields"):
                        qualified_name = _get_qualified_name(type(arg))
                        global_name = add_global(qualified_name, type(arg))
                        return f"{global_name}{repr(tuple(arg))}"
                    return repr(arg)

                args_s = ", ".join(_get_repr(a) for a in args)
                kwargs_s = ", ".join(f"{k} = {_get_repr(v)}" for k, v in kwargs.items())
                if args_s and kwargs_s:
                    return f"{args_s}, {kwargs_s}"
                return args_s or kwargs_s

            # Run through reverse nodes and record the first instance of a use
            # of a given node. This represents the *last* use of the node in the
            # execution order of the program, which we will use to free unused
            # values
            node_to_last_use: Dict[Node, Node] = {}
            user_to_last_uses: Dict[Node, List[Node]] = {}

            def register_last_uses(n: Node, user: Node):
                if n not in node_to_last_use:
                    node_to_last_use[n] = user
                    user_to_last_uses.setdefault(user, []).append(n)

            for node in reversed(nodes):
                map_arg(node.args, lambda n: register_last_uses(n, node))
                map_arg(node.kwargs, lambda n: register_last_uses(n, node))

            _delete_free_var_from_last_use(user_to_last_uses)

            # NOTE: we add a variable to distinguish body and ckpt_func
            def delete_unused_values(user: Node, body, to_keep=[]):
                """
                Delete values after their last use. This ensures that values that are
                not used in the remainder of the code are freed and the memory usage
                of the code is optimal.
                """
                if user.op == "placeholder":
                    return
                if user.op == "output":
                    body.append("\n")
                    return
                nodes_to_delete = user_to_last_uses.get(user, [])
                nodes_to_delete = [i for i in nodes_to_delete if i.name not in to_keep]
                if len(nodes_to_delete):
                    to_delete_str = " = ".join(
                        [repr(n) for n in nodes_to_delete] + ["None"]
                    )
                    body.append(f";  {to_delete_str}\n")
                else:
                    body.append("\n")

            # NOTE: we add a variable to distinguish body and ckpt_func
            def emit_node(node: Node, body):
                maybe_type_annotation = (
                    "" if node.type is None else f" : {type_repr(node.type)}"
                )
                if node.op == "placeholder":
                    assert isinstance(node.target, str)
                    maybe_default_arg = (
                        "" if not node.args else f" = {repr(node.args[0])}"
                    )
                    free_vars.append(
                        f"{node.target}{maybe_type_annotation}{maybe_default_arg}"
                    )
                    raw_name = node.target.replace("*", "")
                    if raw_name != repr(node):
                        body.append(f"{repr(node)} = {raw_name}\n")
                    return
                elif node.op == "call_method":
                    assert isinstance(node.target, str)
                    body.append(
                        f"{repr(node)}{maybe_type_annotation} = {_format_target(repr(node.args[0]), node.target)}"
                        f"({_format_args(node.args[1:], node.kwargs)})"
                    )
                    return
                elif node.op == "call_function":
                    assert callable(node.target)
                    # pretty print operators
                    if (
                        node.target.__module__ == "_operator"
                        and node.target.__name__ in magic_methods
                    ):
                        assert isinstance(node.args, tuple)
                        body.append(
                            f"{repr(node)}{maybe_type_annotation} = "
                            f"{magic_methods[node.target.__name__].format(*(repr(a) for a in node.args))}"
                        )
                        return

                    # pretty print inplace operators; required for jit.script to work properly
                    # not currently supported in normal FX graphs, but generated by torchdynamo
                    if (
                        node.target.__module__ == "_operator"
                        and node.target.__name__ in inplace_methods
                    ):
                        body.append(
                            f"{inplace_methods[node.target.__name__].format(*(repr(a) for a in node.args))};  "
                            f"{repr(node)}{maybe_type_annotation} = {repr(node.args[0])}"
                        )
                        return

                    qualified_name = _get_qualified_name(node.target)
                    global_name = add_global(qualified_name, node.target)
                    # special case for getattr: node.args could be 2-argument or 3-argument
                    # 2-argument: attribute access; 3-argument: fall through to attrib function call with default value
                    if (
                        global_name == "getattr"
                        and isinstance(node.args, tuple)
                        and isinstance(node.args[1], str)
                        and node.args[1].isidentifier()
                        and len(node.args) == 2
                    ):
                        body.append(
                            f"{repr(node)}{maybe_type_annotation} = {_format_target(repr(node.args[0]), node.args[1])}"
                        )
                        return
                    body.append(
                        f"{repr(node)}{maybe_type_annotation} = {global_name}({_format_args(node.args, node.kwargs)})"
                    )
                    if node.meta.get("is_wrapped", False):
                        wrapped_fns.setdefault(global_name)
                    return
                elif node.op == "call_module":
                    assert isinstance(node.target, str)
                    body.append(
                        f"{repr(node)}{maybe_type_annotation} = "
                        f"{_format_target(root_module, node.target)}({_format_args(node.args, node.kwargs)})"
                    )
                    return
                elif node.op == "get_attr":
                    assert isinstance(node.target, str)
                    body.append(
                        f"{repr(node)}{maybe_type_annotation} = {_format_target(root_module, node.target)}"
                    )
                    return
                elif node.op == "output":
                    if node.type is not None:
                        maybe_return_annotation[0] = f" -> {type_repr(node.type)}"
                    body.append(self.generate_output(node.args[0]))
                    return
                raise NotImplementedError(f"node: {node.op} {node.target}")

            # Modified for activation checkpointing
            ckpt_func = []

            # if any node has a list of labels for activation_checkpoint, we
            # will use nested type of activation checkpoint codegen
            emit_code_with_chunk(
                body,
                ckpt_func,
                nodes,
                emit_node,
                delete_unused_values,
                self.meta_node,
                self.meta_graph,
            )

            if len(body) == 0:
                # If the Graph has no non-placeholder nodes, no lines for the body
                # have been emitted. To continue to have valid Python code, emit a
                # single pass statement
                body.append("pass\n")

            if len(wrapped_fns) > 0:
                wrap_name = add_global("wrap", torch.fx.wrap)
                wrap_stmts = "\n".join(
                    [f'{wrap_name}("{name}")' for name in wrapped_fns]
                )
            else:
                wrap_stmts = ""

            if self._body_transformer:
                body = self._body_transformer(body)

            for name, value in self.additional_globals():
                add_global(name, value)

            # as we need colossalai.utils.checkpoint, we need to import colossalai
            # in forward function
            prologue = self.gen_fn_def(free_vars, maybe_return_annotation[0])
            prologue = "".join(ckpt_func) + prologue
            prologue = prologue

            code = "".join(body)
            code = "\n".join("    " + line for line in code.split("\n"))
            fn_code = f"""
{wrap_stmts}

{prologue}
{code}"""
            # print(fn_code)
            return PythonCode(fn_code, globals_)