# Owner(s): ["oncall: distributed"]

import copy
import functools
import io
from copy import deepcopy
from typing import List, Type

import torch
import torch.distributed as dist
import torch.distributed.checkpoint as dcp
import torch.nn as nn
import torch.nn.functional as F
from torch.distributed._composable import replicate
from torch.distributed._composable.fsdp import CPUOffloadPolicy, fully_shard
from torch.distributed._tensor import DTensor, init_device_mesh, Replicate, Shard
from torch.distributed.checkpoint.state_dict import (
    get_model_state_dict,
    get_optimizer_state_dict,
    set_model_state_dict,
    set_optimizer_state_dict,
    StateDictOptions,
)
from torch.distributed.device_mesh import DeviceMesh
from torch.distributed.fsdp import FullyShardedDataParallel as FSDP
from torch.distributed.fsdp._common_utils import (
    _get_module_fsdp_state,
    clean_tensor_name,
)
from torch.distributed.fsdp.fully_sharded_data_parallel import StateDictType
from torch.distributed.tensor.debug import CommDebugMode
from torch.distributed.tensor.parallel import (
    ColwiseParallel,
    parallelize_module,
    RowwiseParallel,
)
from torch.distributed.tensor.parallel.ddp import _pre_dp_module_transform
from torch.distributed.tensor.parallel.fsdp import DTensorExtensions
from torch.distributed.tensor.parallel.input_reshard import input_reshard
from torch.nn.parallel import DistributedDataParallel as DDP
from torch.testing._internal.common_distributed import skip_if_lt_x_gpu
from torch.testing._internal.common_fsdp import FSDPTest, MLP, MLPStack
from torch.testing._internal.common_utils import (
    instantiate_parametrized_tests,
    parametrize,
    run_tests,
    skipIfRocm,
)
from torch.testing._internal.distributed._tensor.common_dtensor import (
    DTensorTestBase,
    MLPModule,
    ModelArgs,
    Transformer,
    with_comms,
)
from torch.testing._internal.distributed.checkpoint_utils import with_temp_dir


class SimpleModel(nn.Module):
    def __init__(self):
        super().__init__()
        self.net1 = nn.Linear(5, 8)
        self.relu = nn.ReLU()
        self.net2 = nn.Linear(8, 4)
        self.net3 = nn.Linear(4, 12)

    def forward(self, x):
        x = F.relu(self.net1(x))
        x = F.relu(self.net2(x))
        x = F.relu(self.net3(x))
        return x

    def get_input(self):
        return torch.rand(4, 5, device="cuda")


class SimpleModelUneven(nn.Module):
    def __init__(self):
        super().__init__()
        torch.manual_seed(0)
        self.net1 = nn.Linear(5, 10)
        self.relu = nn.ReLU()
        self.net2 = nn.Linear(10, 15)
        self.net3 = nn.Linear(15, 30)
        self.net4 = nn.Linear(30, 5)

    def forward(self, x):
        x = F.relu(self.net1(x))
        x = F.relu(self.net2(x))
        x = F.relu(self.net3(x))
        x = self.net4(x)
        return x

    def get_input(self):
        return torch.rand(4, 5, device="cuda")


class TestFullyShard2DTraining(FSDPTest):
    global c10d_ops
    global funcol
    c10d_ops = torch.ops.c10d
    funcol = torch.ops.c10d_functional

    @property
    def world_size(self) -> int:
        return min(4, torch.cuda.device_count())

    def init_global_mesh(self) -> DeviceMesh:
        # Prefer to test with >=4 GPUs, but for 2 GPUs, use 2-way TP
        dp_size = 2 if self.world_size > 2 else 1
        return init_device_mesh(
            "cuda", (dp_size, self.world_size // dp_size), mesh_dim_names=("dp", "tp")
        )

    # TODO: remove this test when uneven sharding is supported for FSDP+TP
    @skip_if_lt_x_gpu(2)
    def test_2d_uneven_shard_raise_error(self):
        global_mesh = self.init_global_mesh()
        dp_mesh, tp_mesh = global_mesh["dp"], global_mesh["tp"]
        model = MLPStack(3)
        with self.assertRaisesRegex(NotImplementedError, "uneven sharding"):
            model.parallelize(tp_mesh, dp_mesh, False)

    @skip_if_lt_x_gpu(2)
    @skipIfRocm
    def test_train_parity_2d_mlp(self):
        global_mesh = self.init_global_mesh()
        self.run_subtests(
            {
                "reshard_after_forward": [False, True],
                "use_activation_checkpointing": [False, True],
                # TODO: change "mlp_dim" back to [3, 16, 17] when uneven sharding
                # is supported for FSDP+TP
                "mlp_dim": [4, 16, 20],
            },
            functools.partial(self._test_train_parity_2d_mlp, global_mesh),
        )

    def _test_train_parity_2d_mlp(
        self,
        global_mesh: DeviceMesh,
        reshard_after_forward: bool,
        use_activation_checkpointing: bool,
        mlp_dim: int,
    ):
        dp_mesh, tp_mesh = global_mesh["dp"], global_mesh["tp"]
        dp_pg = dp_mesh.get_group()  # used for `replicate()`

        torch.manual_seed(42)
        model = MLPStack(mlp_dim)
        ref_model = copy.deepcopy(model).cuda()
        replicate(ref_model, device_ids=[self.rank], process_group=dp_pg)
        ref_optim = torch.optim.Adam(ref_model.parameters(), lr=1e-2, foreach=False)
        model.parallelize(
            tp_mesh,
            dp_mesh,
            use_activation_checkpointing,
            reshard_after_forward=reshard_after_forward,
        )
        optim = torch.optim.Adam(model.parameters(), lr=1e-2, foreach=False)

        torch.manual_seed(42 + dp_pg.rank() + 1)
        device = torch.device("cuda")
        for iter_idx in range(10):
            inp = torch.randn((8, mlp_dim), device=device)
            losses: List[torch.Tensor] = []
            for _model, _optim in ((ref_model, ref_optim), (model, optim)):
                _optim.zero_grad(set_to_none=(iter_idx % 2 == 0))
                losses.append(_model(inp).sum())
                losses[-1].backward()
                _optim.step()
            self.assertEqual(losses[0], losses[1])

    @skip_if_lt_x_gpu(2)
    @skipIfRocm
    def test_tp_with_fsdp_offloading(self):
        global_mesh = init_device_mesh(
            "cuda", (1, self.world_size), mesh_dim_names=("dp", "tp")
        )
        dp_mesh, tp_mesh = global_mesh["dp"], global_mesh["tp"]
        torch.manual_seed(42)
        mlp_dim = 16
        model = MLPStack(mlp_dim)
        ref_model = copy.deepcopy(model).cuda()
        ref_optim = torch.optim.Adam(ref_model.parameters(), lr=1e-2, foreach=False)
        # Parallelize with N-way TP and 1-way FSDP
        model.parallelize(
            tp_mesh,
            dp_mesh,
            use_activation_checkpointing=False,
            reshard_after_forward=True,
            offload_policy=CPUOffloadPolicy(),
        )
        for param in model.parameters():
            self.assertEqual(param.device.type, "cpu")
        num_mlps = sum(isinstance(module, MLP) for module in model.modules())
        optim = torch.optim.Adam(model.parameters(), lr=1e-2, foreach=False)

        # NOTE: We still see the FSDP all-gather/reduce-scatter c10d ops
        # called, but they will just be no-ops without issuing any kernels.
        # We prefer to keep the no-op check at the c10d level, not in FSDP.
        inp = torch.randn((4, mlp_dim), device="cuda")  # same on all ranks
        for iter_idx in range(10):
            ref_optim.zero_grad()
            optim.zero_grad()

            with CommDebugMode() as fwd_comm_mode:
                loss = model(inp).sum()

            fwd_comm_counts = fwd_comm_mode.get_comm_counts()
            self.assertEqual(len(fwd_comm_counts), 2)
            self.assertEqual(fwd_comm_counts[funcol.all_reduce], num_mlps)
            self.assertEqual(fwd_comm_counts[c10d_ops._allgather_base_], num_mlps)
            ref_loss = ref_model(inp).sum()
            self.assertEqual(loss, ref_loss)

            with CommDebugMode() as bwd_comm_mode:
                loss.backward()
            bwd_comm_counts = bwd_comm_mode.get_comm_counts()
            self.assertEqual(len(bwd_comm_counts), 3)
            # First MLP's input gradient does not need to be all-reduced
            self.assertEqual(bwd_comm_counts[funcol.all_reduce], num_mlps - 1)
            self.assertEqual(bwd_comm_counts[c10d_ops._allgather_base_], num_mlps)
            self.assertEqual(bwd_comm_counts[c10d_ops._reduce_scatter_base_], num_mlps)
            ref_loss.backward()

            optim.step()
            ref_optim.step()

    @skip_if_lt_x_gpu(2)
    @with_temp_dir
    def test_train_parity_2d_transformer_checkpoint_resume(self):
        """
        Tests train parity of a 2D transformer without checkpointing against a
        2D transformer with a checkpoint save/load.
        """
        self.run_subtests(
            {
                "use_seq_parallel": [False, True],
                # If reusing, then load into the same model/optimizer instance
                # else construct new ones (requiring eager optim state init)
                "reuse_model_optim": [False, True],
                "optimizer_class": [torch.optim.Adam, torch.optim.AdamW],
                # TODO: need to update `parallelize` before including foreach=True for testing
                "foreach": [False],
            },
            self._test_train_parity_2d_transformer_checkpoint_resume,
        )

    def _test_train_parity_2d_transformer_checkpoint_resume(
        self,
        use_seq_parallel: bool,
        reuse_model_optim: bool,
        optimizer_class: Type[torch.optim.Optimizer],
        foreach: bool,
    ):
        def train_step(
            _model: nn.Module, _optim: torch.optim.Optimizer, _inp: torch.Tensor
        ) -> torch.Tensor:
            loss = _model(_inp).sum()
            loss.backward()
            _optim.step()
            _optim.zero_grad()
            return loss

        def parallelize(_model: Transformer, mesh: DeviceMesh, use_seq_parallel: bool):
            _model = Transformer.parallelize(_model, mesh["tp"], use_seq_parallel)
            for layer in _model.layers:
                fully_shard(layer, mesh=mesh["dp"])
            fully_shard(_model, mesh=mesh["dp"])
            return _model

        global_mesh = self.init_global_mesh()
        # Baseline: run two iterations without checkpointing
        seed = 42
        torch.manual_seed(seed)
        model_args = ModelArgs(dropout_p=0.0)
        model_no_cp = parallelize(
            Transformer(model_args), global_mesh, use_seq_parallel
        )
        optim_no_cp = optimizer_class(
            model_no_cp.parameters(), lr=1e-2, foreach=foreach
        )

        torch.manual_seed(42 + global_mesh["dp"].get_local_rank() + 1)
        inp = torch.randint(0, model_args.vocab_size, (3, 16), device="cuda")
        loss_no_cp1 = train_step(model_no_cp, optim_no_cp, inp)
        loss_no_cp2 = train_step(model_no_cp, optim_no_cp, inp)

        # Test: run one iteration, save checkpoint, zero states or init new
        # model/optimizer, load checkpoint, and run another iteration
        torch.manual_seed(seed)
        model_cp = parallelize(Transformer(model_args), global_mesh, use_seq_parallel)
        optim_cp = optimizer_class(model_cp.parameters(), lr=1e-2, foreach=foreach)

        loss_cp1 = train_step(model_cp, optim_cp, inp)
        self.assertEqual(loss_no_cp1, loss_cp1)

        sharded_sd = {
            "model": get_model_state_dict(model_cp),
            # Use `get_optimizer_state_dict` to handle eager optim state init
            # when constructing a new optimizer instance
            "optim": get_optimizer_state_dict(model_cp, optim_cp),
        }
        dcp.save(
            state_dict=sharded_sd,
            storage_writer=dcp.FileSystemWriter(self.temp_dir),
        )
        if reuse_model_optim:
            with torch.no_grad():
                for param in model_cp.parameters():
                    param.zero_()
                optim_sd = optim_cp.state_dict()
                for param_states in optim_sd["state"].values():
                    for state_value in param_states.values():
                        if torch.is_tensor(state_value):
                            state_value.zero_()
        else:
            torch.manual_seed(seed + 1)  # different seed
            model_cp = parallelize(
                Transformer(model_args), global_mesh, use_seq_parallel
            )
            optim_cp = optimizer_class(model_cp.parameters(), lr=1e-2, foreach=foreach)
        self.assertNotEqual(loss_no_cp2, train_step(model_cp, optim_cp, inp))

        sharded_sd = {
            "model": get_model_state_dict(model_cp),
            "optim": get_optimizer_state_dict(model_cp, optim_cp),
        }
        dcp.load(
            state_dict=sharded_sd,
            storage_reader=dcp.FileSystemReader(self.temp_dir),
        )
        self.assertGreater(len(optim_cp.state_dict()["state"]), 0)

        loss_cp2 = train_step(model_cp, optim_cp, inp)
        self.assertEqual(loss_no_cp2, loss_cp2)


class TestFullyShard2DStateDict(DTensorTestBase):
    @property
    def backend(self):
        # need to specify gloo backend for testing cpu offload
        return "cpu:gloo,cuda:nccl"

    @with_comms
    @skip_if_lt_x_gpu(4)
    def test_fully_shard_tp_2d_set_full_state_dict(self):
        dummy_model = SimpleModel().cuda()
        mesh_2d = init_device_mesh(
            "cuda",
            (2, self.world_size // 2),
            mesh_dim_names=("dp", "tp"),
        )
        tp_mesh = mesh_2d["tp"]
        dp_mesh = mesh_2d["dp"]
        parallelize_plan = {
            "net1": ColwiseParallel(),
            "net2": RowwiseParallel(),
            "net3": ColwiseParallel(),
        }
        model = parallelize_module(dummy_model, tp_mesh, parallelize_plan)
        fully_shard(model, mesh=dp_mesh)
        optim = torch.optim.Adam(model.parameters(), lr=0.01)
        model(model.get_input()).sum().backward()
        optim.step()
        # ref_msd, ref_osd are both the default sharded state dict
        ref_msd = copy.deepcopy(get_model_state_dict(model))
        ref_osd = copy.deepcopy(get_optimizer_state_dict(model, optimizers=optim))

        options = StateDictOptions(
            full_state_dict=True, cpu_offload=True, broadcast_from_rank0=True
        )
        full_msd = get_model_state_dict(model, options=options)
        full_osd = get_optimizer_state_dict(model, optimizers=optim, options=options)
        # load full_msd and full_osd into model and optim.
        # this loads the slice of full tensor into each rank's local DTensor.
        set_model_state_dict(model, full_msd, options=options)
        set_optimizer_state_dict(
            model, optimizers=optim, optim_state_dict=full_osd, options=options
        )

        # check after setting full state dict, the model and optim default sharded state dict
        # are the same as the initial default sharded state dict.
        new_msd = get_model_state_dict(model)
        new_osd = get_optimizer_state_dict(model, optimizers=optim)
        self.assertEqual(ref_msd, new_msd)
        self.assertEqual(ref_osd, new_osd)


class Test2dFSDP1ParallelIntegration(DTensorTestBase):
    def init_model(self, device_type, model_parallel_size=2):
        torch.manual_seed(0)
        model = MLPModule(device_type)
        torch.manual_seed(0)
        twod_model = MLPModule(device_type)
        model = DDP(model)

        # 2-D mesh is [dp, tp]
        world_size = dist.get_world_size()
        mesh_2d = init_device_mesh(
            device_type,
            (world_size // model_parallel_size, model_parallel_size),
            mesh_dim_names=("dp", "tp"),
        )

        dp_pg = mesh_2d.get_group(mesh_dim=0)

        parallelize_plan = {
            "net1": ColwiseParallel(),
            "net2": RowwiseParallel(),
        }
        twod_model = parallelize_module(twod_model, mesh_2d["tp"], parallelize_plan)
        _pre_dp_module_transform(twod_model)
        # TODO: Add tests when using gradient_as_bucket_view and static_graph for DDP.
        twod_model = DDP(twod_model, process_group=dp_pg)
        return model, twod_model, dp_pg

    def _check_module(self, m1, m2, check_grad=False):
        named_parameters = dict(m1.named_parameters())
        for name, param_m2 in m2.named_parameters():
            if name not in named_parameters:
                print(name, named_parameters.keys())
            self.assertTrue(name in named_parameters)
            param_m1 = named_parameters[name]
            if check_grad:
                param_m2 = param_m2.grad
                param_m1 = param_m1.grad
            if isinstance(param_m2, DTensor):
                replicate = [Replicate()]
                param_m2 = param_m2.redistribute(
                    device_mesh=param_m2.device_mesh, placements=replicate
                ).to_local()
            self.assertEqual(param_m2, param_m1)

    @with_comms
    @skip_if_lt_x_gpu(4)
    def test_2d_ddp_integration_functionality(self) -> None:
        model, twod_model, dp_pg = self.init_model(self.device_type)
        optim = torch.optim.Adam(model.parameters(), lr=3e-5)
        twod_optim = torch.optim.Adam(twod_model.parameters(), lr=3e-5)

        # Create Input
        input_seed = dist.get_rank(dp_pg)
        torch.manual_seed(input_seed + 1)
        input = torch.rand(4, 10, device=self.device_type)

        output = model(input)
        twod_output = twod_model(input)
        self.assertEqual(output, twod_output)

        output.sum().backward()
        twod_output.sum().backward()
        self._check_module(model, twod_model, check_grad=True)

        optim.step()
        twod_optim.step()
        self._check_module(model, twod_model)

        torch.manual_seed(input_seed + 1004)
        input = torch.rand(16, 10, device=self.device_type)

        output = model(input)
        twod_output = twod_model(input)
        self.assertEqual(output, twod_output)

        # TODO: Add save/load of 2D verification.


# TODO: add additional tests for multi_param_group, optim_in_backward,
# and fsdp_nested.
class TestNew2dParallelTraining(DTensorTestBase):
    def _compare_params(self, m1, m2):
        with FSDP.summon_full_params(m1):
            with FSDP.summon_full_params(m2):
                for n_p1, n_p2 in zip(m1.named_parameters(), m2.named_parameters()):
                    p1 = n_p1[1]
                    p2 = n_p2[1]
                    if n_p1[0] != n_p2[0]:
                        self.assertTrue(n_p1[0] in n_p2[0])
                    name = n_p1[0]
                    if name == "net2.bias" and self.rank != 0:
                        continue
                    if type(p2) is DTensor:
                        p2 = p2.redistribute(p2.device_mesh, [Replicate()]).to_local()
                    self.assertTrue(torch.allclose(p1, p2), f"{p1} vs {p2}")

    @with_comms
    @skip_if_lt_x_gpu(4)
    def test_raise_invalid_tp_composition(self):
        with self.assertRaisesRegex(
            RuntimeError, r"Found TP device_mesh on the \d dimension of its parent mesh"
        ):
            mesh_2d = init_device_mesh(
                self.device_type, (2, self.world_size // 2), mesh_dim_names=("tp", "dp")
            )
            parallelize_plan = {
                "net1": ColwiseParallel(),
                "net2": RowwiseParallel(),
            }
            model_2d = parallelize_module(
                SimpleModel().cuda(), mesh_2d["tp"], parallelize_plan
            )

    @with_comms
    @skip_if_lt_x_gpu(4)
    def test_2d_fsdp_state_enable_extension(self):
        mesh_2d = init_device_mesh(
            self.device_type, (2, self.world_size // 2), mesh_dim_names=("dp", "tp")
        )
        model = FSDP(
            SimpleModel().cuda(),
            device_mesh=mesh_2d["dp"],
        )
        fsdp_state = _get_module_fsdp_state(model)
        self.assertTrue(isinstance(fsdp_state._fsdp_extension, DTensorExtensions))

    def _test_2d_e2e_training(
        self,
        use_orig_params=False,
        recompute_activation=False,
    ) -> None:
        torch.manual_seed(0)
        model = SimpleModel().cuda(self.rank)
        model = FSDP(model, use_orig_params=use_orig_params)
        optim = torch.optim.Adam(model.parameters(), lr=0.01)

        torch.manual_seed(0)
        mesh_2d = init_device_mesh(
            self.device_type, (2, self.world_size // 2), mesh_dim_names=("dp", "tp")
        )
        tp_mesh = mesh_2d["tp"]
        dp_mesh = mesh_2d["dp"]
        parallelize_plan = {
            "net1": ColwiseParallel(),
            "net2": RowwiseParallel(),
        }
        model_2d = parallelize_module(SimpleModel().cuda(), tp_mesh, parallelize_plan)
        model_2d = FSDP(
            model_2d,
            device_mesh=dp_mesh,
            use_orig_params=use_orig_params,
        )
        optim_2d = torch.optim.Adam(model_2d.parameters(), lr=0.01)

        if recompute_activation:
            model_2d = input_reshard(model_2d, mesh_2d["tp"], 0)

        # Check named parameters are returning the same name at least.
        param_names_2d = [
            clean_tensor_name(name) for name, _ in model_2d.named_parameters()
        ]
        for name, _ in model.named_parameters():
            name = clean_tensor_name(name)
            if name not in param_names_2d:
                print(name, param_names_2d)
            self.assertTrue(name in param_names_2d)
        self._compare_params(model, model_2d)

        # TODO: add additional tests for multi_param_group and optim_in_backward.

        for i in range(5):
            # Ensure all input across TP ranks are same.
            # TODO: add a get_group_rank() to DeviceMesh.
            torch.manual_seed(i + dist.get_rank(dp_mesh.get_group(mesh_dim=0)))
            input = torch.rand(4, 5).cuda(self.rank)
            output = model(input)
            output_2d = model_2d(input)
            self.assertEqual(output, output_2d)
            output.sum().backward()
            output_2d.sum().backward()
            optim.step()
            optim_2d.step()
            self.assertEqual(model(input), model_2d(input))

        # Ensure all params are still the same after optimizer update.
        self._compare_params(model, model_2d)

    @with_comms
    @skip_if_lt_x_gpu(4)
    def test_2d_e2e_training_default(self):
        self._test_2d_e2e_training()

    @with_comms
    @skip_if_lt_x_gpu(4)
    def test_2d_e2e_training_use_orig_params(self):
        self._test_2d_e2e_training(use_orig_params=True)

    @with_comms
    @skip_if_lt_x_gpu(4)
    def test_2d_e2e_training_not_use_orig_params(self):
        # TODO: need to revisit input_reshard API about why it failed multi-gpu tests.
        # self._test_2d_e2e_training(recompute_activation=True)
        self._test_2d_e2e_training(recompute_activation=False)


# TODO: update all state dict unit tests to use distributed.checkpoint.state_dict,
# and consolidate all the state_dict test in test.distributed.checkpoint.
class TestNew2dParallelStateDict(DTensorTestBase):
    @property
    def backend(self):
        # need to specify gloo backend for testing cpu offload
        return "cpu:gloo,cuda:nccl"

    @with_comms
    @skip_if_lt_x_gpu(4)
    def test_fsdp_2d_extension(self):
        """
        Test whether _fsdp_extension from FSDPstate has been set correctly.
        """
        mesh_2d = init_device_mesh(
            self.device_type, (2, self.world_size // 2), mesh_dim_names=("dp", "tp")
        )
        parallelize_plan = {
            "net1": ColwiseParallel(),
            "net2": RowwiseParallel(),
            "net3": ColwiseParallel(),
        }
        model_2d = parallelize_module(
            SimpleModel().cuda(),
            mesh_2d["tp"],
            parallelize_plan=parallelize_plan,
        )
        model_2d = FSDP(model_2d, device_mesh=mesh_2d["dp"], use_orig_params=True)
        model_2d_fsdp_state = _get_module_fsdp_state(model_2d)
        self.assertTrue(
            isinstance(model_2d_fsdp_state._fsdp_extension, DTensorExtensions)
        )

        mesh_1d = init_device_mesh("cuda", (self.world_size,))
        model_1d = FSDP(SimpleModel().cuda(), device_mesh=mesh_1d, use_orig_params=True)
        model_1d_fsdp_state = _get_module_fsdp_state(model_1d)
        self.assertEqual(model_1d_fsdp_state._fsdp_extension, None)

    @with_comms
    @skip_if_lt_x_gpu(4)
    @parametrize("is_even_sharded_model", [True, False])
    def test_2d_state_dict(self, is_even_sharded_model):
        simple_model = SimpleModel if is_even_sharded_model else SimpleModelUneven

        # Create a model without wrapper
        torch.manual_seed(0)
        no_wrap_model = simple_model().cuda(self.rank)
        no_wrap_state_dict = no_wrap_model.state_dict()

        # Create a model and sharded it with 2D FSDP + TP
        torch.manual_seed(0)
        mesh_2d = init_device_mesh(
            self.device_type, (2, self.world_size // 2), mesh_dim_names=("dp", "tp")
        )
        tp_mesh = mesh_2d["tp"]
        dp_mesh = mesh_2d["dp"]
        parallelize_plan = {
            "net1": ColwiseParallel(),
            "net2": RowwiseParallel(),
        }
        model_2d = parallelize_module(simple_model().cuda(), tp_mesh, parallelize_plan)
        model_2d = FSDP(model_2d, device_mesh=dp_mesh, use_orig_params=True)

        FSDP.set_state_dict_type(
            model_2d,
            StateDictType.SHARDED_STATE_DICT,
        )
        state_dict_2d = model_2d.state_dict()

        for no_wrap_items, two_d_items in zip(
            no_wrap_state_dict.items(), state_dict_2d.items()
        ):
            no_wrap_k, no_wrap_v = no_wrap_items
            two_d_k, two_d_v = two_d_items

            self.assertEqual(no_wrap_k, two_d_k)

            # check if all value in 2D state_dict are DTensor
            self.assertTrue(isinstance(two_d_v, DTensor))
            self.assertEqual(len(two_d_v.placements), 2)
            # the outer dimension is the FSDP dimension and the placement is always Shard(0)
            self.assertEqual(two_d_v.placements[0], Shard(0))
            self.assertEqual(two_d_v.device_mesh, mesh_2d)

            # check if the parameter value is the same between 2D model and the model without wrapper
            all_gather_two_d_v = two_d_v.redistribute(
                mesh_2d, (Replicate(), Replicate())
            )
            self.assertEqual(
                torch.allclose(no_wrap_v, all_gather_two_d_v.to_local()), True
            )

    @with_comms
    @skip_if_lt_x_gpu(4)
    @parametrize("is_even_sharded_model", [True, False])
    def test_2d_load_state_dict(self, is_even_sharded_model):
        simple_model = SimpleModel if is_even_sharded_model else SimpleModelUneven

        torch.manual_seed(0)
        mesh_2d = init_device_mesh(
            self.device_type, (2, self.world_size // 2), mesh_dim_names=("dp", "tp")
        )
        tp_mesh = mesh_2d["tp"]
        dp_mesh = mesh_2d["dp"]
        parallelize_plan = {
            "net1": ColwiseParallel(),
            "net2": RowwiseParallel(),
        }
        model_2d = parallelize_module(simple_model().cuda(), tp_mesh, parallelize_plan)
        model_2d = FSDP(model_2d, device_mesh=dp_mesh, use_orig_params=True)
        optim_2d = torch.optim.Adam(model_2d.parameters(), lr=0.01)

        FSDP.set_state_dict_type(
            model_2d,
            StateDictType.SHARDED_STATE_DICT,
        )
        checkpoint = io.BytesIO()
        torch.save(model_2d.state_dict(), checkpoint)
        # Deepcopy to save current state_dict to compare with the state_dict loaded back below.
        ref_state_dict = deepcopy(model_2d.state_dict())

        # Update the parameters so model.state_dict() will be different from ref_dtensor_sd.
        model_2d(model_2d.get_input().cuda(self.rank)).sum().backward()
        optim_2d.step()

        # Load ref_state_dict back.
        checkpoint.seek(0)
        load_ref_state_dict = torch.load(checkpoint)
        model_2d.load_state_dict(load_ref_state_dict)
        new_state_dict = model_2d.state_dict()

        # Check whether new_state_dict is the same as ref_state_dict.
        for (k1, v1), (k2, v2) in zip(ref_state_dict.items(), new_state_dict.items()):
            # check whether fqn are the same
            self.assertEqual(k1, k2)

            self.assertEqual(type(v1), DTensor)
            self.assertEqual(type(v2), DTensor)
            # check whether DTensor are the same
            # TODO: 2D DTensor comparison is not supported at the time, so we are comparing the spec and the local tensor for now.
            # TODO: Update it to compare the two DTensors once 2D DTensor comparison is supported.
            self.assertEqual(v1.to_local(), v2.to_local())
            self.assertEqual(v1.device_mesh, v2.device_mesh)
            self.assertEqual(v1.placements, v2.placements)

    @with_comms
    @skip_if_lt_x_gpu(4)
    @parametrize("is_even_sharded_model", [True, False])
    def test_2d_optim_state_dict(self, is_even_sharded_model):
        simple_model = SimpleModel if is_even_sharded_model else SimpleModelUneven

        # Create a model without wrapper
        torch.manual_seed(0)
        no_wrap_model = simple_model().cuda(self.rank)
        no_wrap_state_dict = no_wrap_model.state_dict()
        no_wrap_optim = torch.optim.Adam(no_wrap_model.parameters(), lr=0.01)
        no_wrap_model(no_wrap_model.get_input().cuda(self.rank)).sum().backward()
        no_wrap_optim.step()
        no_wrap_osd = get_optimizer_state_dict(no_wrap_model, optimizers=no_wrap_optim)

        # Create a model and sharded it with 2D FSDP + TP
        torch.manual_seed(0)
        mesh_2d = init_device_mesh(
            self.device_type, (2, self.world_size // 2), mesh_dim_names=("dp", "tp")
        )
        parallelize_plan = {
            "net1": ColwiseParallel(),
            "net2": RowwiseParallel(),
        }
        model_2d = parallelize_module(
            simple_model().cuda(), mesh_2d["tp"], parallelize_plan
        )
        model_2d = FSDP(model_2d, device_mesh=mesh_2d["dp"], use_orig_params=True)
        FSDP.set_state_dict_type(
            model_2d,
            StateDictType.SHARDED_STATE_DICT,
        )
        optim_2d = torch.optim.Adam(model_2d.parameters(), lr=0.01)
        model_2d(model_2d.get_input().cuda(self.rank)).sum().backward()
        optim_2d.step()
        optim_2d_osd = get_optimizer_state_dict(model_2d, optimizers=optim_2d)
        ref_optim_2d_osd = deepcopy(optim_2d_osd)

        no_wrap_osd_states = no_wrap_osd["state"]
        optim_2d_osd_states = optim_2d_osd["state"]

        self.assertEqual(len(no_wrap_osd_states), len(optim_2d_osd_states))
        self.assertEqual(no_wrap_osd_states.keys(), optim_2d_osd_states.keys())
        for fqn, states in no_wrap_osd_states.items():
            dist_states = optim_2d_osd_states.get(fqn)

            for state_name, state in states.items():
                dist_state = dist_states.get(state_name)
                # If a state  is DTensor, we all gather it in both DP and TP dimension to
                # compare with no_wrap state.
                if isinstance(dist_state, DTensor):
                    dist_state = (
                        dist_state.cuda()
                        .redistribute(placements=(Replicate(), Replicate()))
                        .to_local()
                    )
                self.assertTrue(isinstance(dist_state, torch.Tensor))
                self.assertTrue(torch.allclose(state, dist_state))

        # Update the parameters 2d optim states will be different from ref_optim_state_dict.
        model_2d(model_2d.get_input().cuda(self.rank)).sum().backward()
        optim_2d.step()

        set_optimizer_state_dict(
            model_2d, optimizers=optim_2d, optim_state_dict=ref_optim_2d_osd
        )
        new_optim_2d_osd = get_optimizer_state_dict(model_2d, optimizers=optim_2d)

        ref_optim_2d_osd_states = ref_optim_2d_osd["state"]
        new_optim_2d_osd_states = optim_2d_osd["state"]

        # Compare the new optim state dict after load with the reference one
        self.assertEqual(len(ref_optim_2d_osd_states), len(new_optim_2d_osd_states))
        self.assertEqual(ref_optim_2d_osd_states.keys(), new_optim_2d_osd_states.keys())
        for fqn, states in ref_optim_2d_osd_states.items():
            new_states = new_optim_2d_osd_states.get(fqn)

            for state_name, state in states.items():
                new_state = new_states.get(state_name)

                if isinstance(new_state, DTensor):
                    self.assertEqual(new_state.placements, state.placements)
                    self.assertEqual(new_state.device_mesh, state.device_mesh)
                    self.assertTrue(
                        torch.allclose(new_state.to_local(), state.to_local())
                    )
                else:
                    self.assertEqual(new_state, state)


instantiate_parametrized_tests(TestNew2dParallelStateDict)

if __name__ == "__main__":
    run_tests()
