fla/layers/gated_deltanet.py

# -*- coding: utf-8 -*-
# Copyright (c) 2023-2025, Songlin Yang, Yu Zhang

from __future__ import annotations

import math
from typing import TYPE_CHECKING, Dict, Optional, Tuple

import torch
import torch.nn as nn
from einops import rearrange
from torch.nn import functional as F

from fla.modules import FusedRMSNormGated, RMSNorm, ShortConvolution
from fla.ops.gated_delta_rule import chunk_gated_delta_rule, fused_recurrent_gated_delta_rule

if TYPE_CHECKING:
    from transformers.processing_utils import Unpack

    from fla.models.utils import Cache


@torch.compile
def elu_p1(x):
    return (F.elu(x, 1., False) + 1.).to(x)


@torch.compile
def sum_norm(x):
    return (x / x.sum(-1, keepdim=True)).to(x)


class GatedDeltaNet(nn.Module):
    """
    The layer implementaion for [Gated Delta Networks: Improving Mamba2 with Delta Rule](https://arxiv.org/abs/2412.06464).  # noqa

    Similar to Mamba2, each layer contains around 6*hidden_size*hidden_size parameters.

    Parameter alloation when use_gate=True:
        - 0.75 * hidden_size * hidden_size for the q_proj and k_proj each
        - 1.5 * hidden_size * hidden_size for the v_proj, g_proj and o_proj each
        - Others are ignorably small.
        - In total = 0.75 * 2 + 1.5 * 3 = 6 * hidden_size * hidden_size
    NOTE: num_heads * head_dim = 0.75 * hidden_size, please make sure to set the correct num_heads and head_dim.

    Parameter allocation when use_gate=False:
        - 1 * hidden_size * hidden_size for the q_proj and k_proj each
        - 2 * hidden_size * hidden_size for the v_proj and o_proj each
        - Others are ignorably small.
        - In total = 1 * 2 + 2 * 2 = 6 * hidden_size * hidden_size

    Args:
        hidden_size (int, Optional):
            The hidden size of the input. Default: 2048.
        expand_v (float, Optional):
            The expansion ratio for the value dim. Default: 2.0.
        head_dim (int, Optional):
            The dimension of each head. Default: 256.
        num_heads (int, Optional):
            The number of heads. Default: 4.
        mode (str, Optional):
            Which Gated DeltaNet kernel to use.
            Currently available: `chunk` and `fused_recurrent`.
            Default: `chunk`.
        use_beta (bool, Optional):
            Whether to use beta. Default: `True`.
        use_gate (bool, Optional):
            Whether to use output gate. Default: `True`.
        use_short_conv (bool, Optional):
            Whether to use short convolutions. Default: `True`.
        conv_size (int, Optional):
            The kernel size of the short convolution, only used when `use_short_conv` is `True`. Default: 4.
        conv_bias (bool, Optional):
            Whether to use bias in the short convolution, only used when `use_short_conv` is `True`. Default: `False`.
        layer_idx (int, Optional):
            The index of the layer. Default: None.
        norm_eps (float, Optional):
            The epsilon value for the normalization layer. Default: 1e-5.
    """

    def __init__(
        self,
        hidden_size: int = 2048,
        expand_v: float = 2,
        head_dim: int = 256,
        num_heads: int = 6,
        mode: str = 'chunk',
        use_gate: bool = True,
        use_short_conv: bool = True,
        conv_size: int = 4,
        conv_bias: bool = False,
        layer_idx: int = None,
        norm_eps: float = 1e-5,
        **kwargs
    ) -> GatedDeltaNet:
        super().__init__()

        self.mode = mode

        self.hidden_size = hidden_size
        self.expand_v = expand_v

        self.use_gate = use_gate
        self.use_short_conv = use_short_conv
        self.conv_size = conv_size
        self.conv_bias = conv_bias

        self.head_dim = head_dim
        self.num_heads = num_heads

        self.key_dim = int(self.num_heads * self.head_dim)
        self.value_dim = int(self.key_dim * self.expand_v)
        self.head_k_dim = head_dim
        self.head_v_dim = int(head_dim * self.expand_v)
        self.layer_idx = layer_idx

        # Consistency check: Ensure expand_v produces integer values
        if not math.isclose(self.key_dim * expand_v, self.value_dim, rel_tol=1e-5):
            raise ValueError(
                f"expand_v={expand_v} does not produce an integer value when multiplied by key_dim={self.key_dim}. "
                f"Resulting value_dim would be {self.key_dim * expand_v}, which is invalid for nn.Linear."
            )
        if not math.isclose(head_dim * expand_v, self.head_v_dim, rel_tol=1e-5):
            raise ValueError(
                f"expand_v={expand_v} does not produce an integer value when multiplied by head_dim={head_dim}. "
                f"Resulting head_v_dim would be {head_dim * expand_v}, which is invalid for FusedRMSNormGated."
            )
        assert mode in ['chunk', 'fused_recurrent'], f"Not suppoerted mode `{mode}`."

        self.q_proj = nn.Linear(hidden_size, self.key_dim, bias=False)
        self.k_proj = nn.Linear(hidden_size, self.key_dim, bias=False)
        self.v_proj = nn.Linear(hidden_size, self.value_dim, bias=False)
        self.a_proj = nn.Linear(hidden_size, self.num_heads, bias=False)
        self.b_proj = nn.Linear(hidden_size, self.num_heads, bias=False)

        A = torch.empty(self.num_heads, dtype=torch.float32).uniform_(0, 16)
        self.A_log = nn.Parameter(torch.log(A))
        self.A_log._no_weight_decay = True
        # hard coded for now
        dt_min = 0.001
        dt_max = 0.1
        dt_init_floor = 1e-4
        dt = torch.exp(
            torch.rand(self.num_heads) * (math.log(dt_max) - math.log(dt_min))
            + math.log(dt_min)
        )
        dt = torch.clamp(dt, min=dt_init_floor)
        # Inverse of softplus: https://github.com/pytorch/pytorch/issues/72759
        inv_dt = dt + torch.log(-torch.expm1(-dt))
        self.dt_bias = nn.Parameter(inv_dt)
        # Just to be explicit. Without this we already don't put wd on dt_bias because of the check
        # name.endswith("bias") in param_grouping.py
        self.dt_bias._no_weight_decay = True

        if use_short_conv:
            self.conv_size = conv_size
            self.q_conv1d = ShortConvolution(
                hidden_size=self.key_dim,
                kernel_size=conv_size,
                activation='silu'
            )
            self.k_conv1d = ShortConvolution(
                hidden_size=self.key_dim,
                kernel_size=conv_size,
                activation='silu'
            )
            self.v_conv1d = ShortConvolution(
                hidden_size=self.value_dim,
                kernel_size=conv_size,
                activation='silu'
            )
        else:
            raise UserWarning(
                "ShortConvolution is crucial to the performance. "
                "Do not turn it off, i.e., setting `use_short_conv=False` unless you know what you are doing."
            )
        if use_gate:
            self.g_proj = nn.Linear(hidden_size, self.value_dim, bias=False)
            self.o_norm = FusedRMSNormGated(self.head_v_dim, eps=norm_eps)
        else:
            self.o_norm = RMSNorm(self.head_v_dim, eps=norm_eps)
        self.o_proj = nn.Linear(self.value_dim, hidden_size, bias=False)

    def forward(
        self,
        hidden_states: torch.Tensor,
        attention_mask: Optional[torch.Tensor] = None,
        past_key_values: Optional[Cache] = None,
        use_cache: Optional[bool] = False,
        output_attentions: Optional[bool] = False,
        **kwargs: Unpack[Dict]
    ) -> Tuple[torch.Tensor, Optional[torch.Tensor], Optional[Cache]]:
        if attention_mask is not None:
            assert len(attention_mask.shape) == 2, (
                "Expected attention_mask as a 0-1 matrix with shape [batch_size, seq_len] "
                "for padding purposes (0 indicating padding). "
                "Arbitrary attention masks of shape [batch_size, seq_len, seq_len] are not allowed."
            )

        mode = 'fused_recurrent' if hidden_states.shape[1] <= 64 else self.mode
        if self.training:
            assert mode == 'chunk', "Only chunk mode is supported in training."

        last_state = None
        if past_key_values is not None and len(past_key_values) > self.layer_idx:
            last_state = past_key_values[self.layer_idx]

        cu_seqlens = kwargs.get('cu_seqlens', None)
        if self.use_short_conv:
            conv_state_q, conv_state_k, conv_state_v = None, None, None
            if last_state is not None:
                conv_state_q, conv_state_k, conv_state_v = last_state['conv_state']
            conv_mask = attention_mask[:, -hidden_states.shape[1]:] if attention_mask is not None else None
            q, conv_state_q = self.q_conv1d(
                x=self.q_proj(hidden_states),
                mask=conv_mask,
                cache=conv_state_q,
                output_final_state=use_cache,
                cu_seqlens=cu_seqlens
            )
            k, conv_state_k = self.k_conv1d(
                x=self.k_proj(hidden_states),
                mask=conv_mask,
                cache=conv_state_k,
                output_final_state=use_cache,
                cu_seqlens=cu_seqlens
            )
            v, conv_state_v = self.v_conv1d(
                x=self.v_proj(hidden_states),
                mask=conv_mask,
                cache=conv_state_v,
                output_final_state=use_cache,
                cu_seqlens=cu_seqlens
            )
        else:
            q = F.silu(self.q_proj(hidden_states))
            k = F.silu(self.k_proj(hidden_states))
            v = F.silu(self.v_proj(hidden_states))

        q, k = map(lambda x: rearrange(x, 'b t (h d) -> b t h d', d=self.head_k_dim), (q, k))
        v = rearrange(v, 'b t (h d) -> b t h d', d=self.head_v_dim)
        beta = self.b_proj(hidden_states).sigmoid()
        g = -self.A_log.float().exp() * F.softplus(self.a_proj(hidden_states).float() + self.dt_bias)

        # dealing with padding
        if attention_mask is not None:
            beta = beta.mul(attention_mask[:, -beta.shape[-2]:, None])
            g = g.mul(attention_mask[:, -g.shape[-2]:, None])

        recurrent_state = last_state['recurrent_state'] if last_state is not None else None
        if mode == 'chunk':
            o, recurrent_state = chunk_gated_delta_rule(
                q=q,
                k=k,
                v=v,
                g=g,
                beta=beta,
                initial_state=recurrent_state,
                output_final_state=use_cache,
                cu_seqlens=cu_seqlens,
                head_first=False,
                use_qk_l2norm_in_kernel=True
            )
        elif mode == 'fused_recurrent':
            o, recurrent_state = fused_recurrent_gated_delta_rule(
                q=q,
                k=k,
                v=v,
                g=g,
                beta=beta,
                initial_state=recurrent_state,
                output_final_state=use_cache,
                cu_seqlens=cu_seqlens,
                head_first=False,
                use_qk_l2norm_in_kernel=True
            )
        if past_key_values is not None:
            past_key_values.update(
                recurrent_state=recurrent_state,
                conv_state=(conv_state_q, conv_state_k, conv_state_v) if self.use_short_conv else None,
                layer_idx=self.layer_idx,
                offset=q.shape[1]
            )

        if self.use_gate:
            g = rearrange(self.g_proj(hidden_states), '... (h d) -> ... h d', d=self.head_v_dim)
            o = self.o_norm(o, g)
        else:
            o = self.o_norm(o)
        o = rearrange(o, 'b t h d -> b t (h d)')
        o = self.o_proj(o)

        return o, None, past_key_values