mirror of
https://github.com/ml-explore/mlx-examples.git
synced 2025-06-26 02:33:23 +08:00
309 lines
11 KiB
Python
309 lines
11 KiB
Python
import math
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from dataclasses import dataclass, field
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from typing import Tuple, Union
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import mlx.core as mx
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import mlx.nn as nn
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from .base import BaseModelArgs
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from .cache import MambaCache
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@dataclass
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class ModelArgs(BaseModelArgs):
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num_heads: int
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head_dim: int
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vocab_size: int
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hidden_size: int
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state_size: int
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num_hidden_layers: int
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layer_norm_epsilon: float
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expand: int
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conv_kernel: int
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n_groups: int
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use_bias: bool
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use_conv_bias: bool
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initializer_range: float
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residual_in_fp32: bool
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time_step_min: float
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time_step_max: float
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time_step_floor: float
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rescale_prenorm_residual: bool
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rms_norm: bool
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chunk_size: int
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tie_word_embeddings: bool
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use_cache: bool = True
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time_step_limit: Tuple[float, float] = field(default_factory=lambda: (0.0, float("inf")))
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time_step_rank: Union[int, str] = "auto"
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model_type: str = "mamba2"
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def __post_init__(self):
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if not hasattr(self, "intermediate_size"):
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self.intermediate_size = int(self.expand * self.hidden_size)
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if not hasattr(self, "head_dim"):
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self.head_dim = self.hidden_size // self.num_heads
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if self.time_step_rank == "auto":
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self.time_step_rank = math.ceil(self.hidden_size / 16)
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class MambaRMSNormGated(nn.Module):
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def __init__(self, hidden_size, eps=1e-6):
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super().__init__()
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self.weight = mx.ones((hidden_size,))
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self.variance_epsilon = eps
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def __call__(self, hidden_states, gate=None):
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if gate is not None:
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hidden_states = hidden_states * nn.silu(gate)
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variance = mx.mean(hidden_states ** 2, axis=-1, keepdims=True)
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hidden_states = hidden_states * mx.rsqrt(variance + self.variance_epsilon)
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return self.weight * hidden_states
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def silu(x):
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return x * mx.sigmoid(x)
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def ssd(x, A, B, C, chunk_size):
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batch, seqlen, nheads, dim = x.shape
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B = mx.expand_dims(B, axis=2)
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C = mx.expand_dims(C, axis=2)
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state = mx.zeros((batch, nheads, dim, B.shape[-1]))
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outputs = []
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for i in range(0, seqlen, chunk_size):
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chunk = slice(i, min(i + chunk_size, seqlen))
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dA = mx.exp(mx.expand_dims(A[chunk], axis=0))
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x_chunk = x[:, chunk] # [batch, chunk_size, nheads, dim]
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x_chunk = mx.transpose(x_chunk, [0, 2, 3, 1]) # [batch, nheads, dim, chunk_size]
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B_chunk = B[:, chunk] # [batch, chunk_size, state_size]
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dBx = mx.matmul(x_chunk, B_chunk) # [batch, nheads, dim, state_size]
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state = state * mx.expand_dims(dA, axis=-1) + dBx
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C_chunk = C[:, chunk] # [batch, chunk_size, state_size]
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y = mx.matmul(state, mx.transpose(C_chunk, [0, 2, 1])) # [batch, nheads, dim, chunk_size]
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y = mx.transpose(y, [0, 3, 1, 2]) # [batch, chunk_size, nheads, dim]
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outputs.append(y)
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return mx.concatenate(outputs, axis=1), state
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class DepthWiseConv1d(nn.Module):
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def __init__(self, channels, kernel_size, bias=True, padding=0):
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super().__init__()
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self.channels = channels
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self.kernel_size = kernel_size
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self.padding = padding
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self.weight = mx.random.normal((self.channels, kernel_size, 1))
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self.bias = mx.zeros((channels,)) if bias else None
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def __call__(self, x, cache=None):
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B, L, C = x.shape
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groups, K, _ = self.weight.shape
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if cache is not None:
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x = mx.concatenate([cache, x], axis=1)
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else:
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x = mx.pad(x, [(0, 0), (K - 1, 0), (0, 0)])
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y = mx.conv_general(x, self.weight, groups=groups)
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if self.bias is not None:
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y = y + self.bias
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return y, x[:, -K + 1:, :]
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class Mamba2Block(nn.Module):
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def __init__(self, args: ModelArgs):
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super().__init__()
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self.args = args
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# Calculate dimensions
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self.d_model = args.hidden_size
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self.d_state = args.state_size
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self.d_conv = args.conv_kernel
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self.expand = args.expand
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self.d_inner = int(self.expand * self.d_model)
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self.n_heads = args.num_heads
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self.d_head = self.d_inner // self.n_heads
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# Input projection
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d_in_proj = self.d_inner * 2 + self.d_state * 2 + self.n_heads
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self.in_proj = nn.Linear(self.d_model, d_in_proj, bias=args.use_bias)
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# Convolution
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conv_dim = self.d_inner + 2 * self.d_state
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self.conv1d = DepthWiseConv1d(
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channels=conv_dim,
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kernel_size=self.d_conv,
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bias=args.use_conv_bias
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)
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# SSM parameters
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self.dt_bias = mx.random.normal((self.n_heads,)) * args.initializer_range
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self.A_log = mx.random.normal((self.n_heads,)) * args.initializer_range
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self.D = mx.random.normal((self.n_heads,)) * args.initializer_range
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# Output projection
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self.norm = MambaRMSNormGated(self.d_inner, eps=args.layer_norm_epsilon)
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self.out_proj = nn.Linear(self.d_inner, self.d_model, bias=args.use_bias)
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if args.rescale_prenorm_residual:
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layer_scale = math.sqrt(1.0 / args.num_hidden_layers)
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self.out_proj.weight = self.out_proj.weight * layer_scale
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def __call__(self, u: mx.array, cache=None):
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batch_size, seq_len, _ = u.shape
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# Project input
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proj = self.in_proj(u) # [batch, seq_len, d_in_proj]
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# Calculate split indices and slice tensors
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z = proj[..., :self.d_inner]
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x_conv = proj[..., self.d_inner:self.d_inner + (self.d_inner + 2 * self.d_state)]
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dt = proj[..., -self.n_heads:]
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# Process time steps
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dt = nn.softplus(dt + self.dt_bias)
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dt = mx.clip(dt, self.args.time_step_min, self.args.time_step_max)
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dt = mx.maximum(dt, self.args.time_step_floor)
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# Convolution and activation
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x_conv, conv_state = self.conv1d(x_conv, cache[0] if cache else None)
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if cache is not None:
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cache[0] = conv_state
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x_conv = silu(x_conv)
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# Split conv output
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x = x_conv[..., :self.d_inner]
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B = x_conv[..., self.d_inner:self.d_inner + self.d_state]
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C = x_conv[..., -self.d_state:]
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# Reshape x for SSM
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x = mx.reshape(x, (batch_size, seq_len, self.n_heads, self.d_head))
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# Process B and C without reshaping heads
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B = mx.expand_dims(B, axis=2) # [batch, seq_len, 1, d_state]
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B = mx.broadcast_to(B, (batch_size, seq_len, self.n_heads, self.d_state))
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C = mx.expand_dims(C, axis=2) # [batch, seq_len, 1, d_state]
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C = mx.broadcast_to(C, (batch_size, seq_len, self.n_heads, self.d_state))
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# Initialize or get previous state
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if cache and cache[1] is not None:
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prev_state = cache[1]
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else:
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prev_state = mx.zeros((batch_size, self.n_heads, self.d_head, self.d_state))
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# Compute dA
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dA = -mx.exp(self.A_log) # [n_heads]
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dt = mx.reshape(dt, (batch_size, seq_len, self.n_heads)) # Ensure correct shape
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dA = mx.exp(mx.expand_dims(dt * mx.expand_dims(dA, 0), -1)) # [batch, seq_len, n_heads, 1]
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dA = mx.expand_dims(dA, -1) # [batch, seq_len, n_heads, 1, 1]
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# Process sequence
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next_state = prev_state
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outputs = []
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for t in range(seq_len):
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# Get current step tensors
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xt = x[:, t] # [batch, n_heads, d_head]
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Bt = B[:, t] # [batch, n_heads, d_state]
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Ct = C[:, t] # [batch, n_heads, d_state]
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dAt = dA[:, t] # [batch, n_heads, 1, 1]
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# Update state
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next_state = (
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next_state * dAt + # Broadcasting: [batch, n_heads, d_head, d_state] * [batch, n_heads, 1, 1]
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mx.matmul(
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mx.expand_dims(xt, -1), # [batch, n_heads, d_head, 1]
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mx.expand_dims(Bt, -2) # [batch, n_heads, 1, d_state]
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)
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)
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# Compute output
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yt = mx.matmul(
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next_state, # [batch, n_heads, d_head, d_state]
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mx.expand_dims(Ct, -1) # [batch, n_heads, d_state, 1]
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)
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yt = mx.squeeze(yt, -1) # [batch, n_heads, d_head]
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yt = yt + xt * mx.expand_dims(self.D, -1)
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# Reshape and normalize
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yt = mx.reshape(yt, (batch_size, 1, self.d_inner))
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yt = self.norm(yt, z[:, t:t+1])
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outputs.append(self.out_proj(yt))
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# Update cache
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if cache is not None:
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cache[1] = next_state
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return mx.concatenate(outputs, axis=1)
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class ResidualBlock(nn.Module):
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def __init__(self, args: ModelArgs):
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super().__init__()
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self.residual_in_fp32 = args.residual_in_fp32
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self.mixer = Mamba2Block(args)
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self.norm = nn.RMSNorm(args.hidden_size)
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def __call__(self, x: mx.array, cache):
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if self.residual_in_fp32:
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x = x.astype(mx.float32)
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normed = self.norm(x)
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output = self.mixer(normed, cache)
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return output + x
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class Mamba2(nn.Module):
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def __init__(self, args: ModelArgs):
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super().__init__()
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self.args = args
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self.embeddings = nn.Embedding(args.vocab_size, args.hidden_size)
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self.layers = [ResidualBlock(args) for _ in range(args.num_hidden_layers)]
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self.norm_f = nn.RMSNorm(args.hidden_size, eps=args.layer_norm_epsilon)
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def __call__(self, x: mx.array, cache):
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x = self.embeddings(x)
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if cache is None:
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cache = [None] * len(self.layers)
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hidden = x
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for layer, c in zip(self.layers, cache):
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hidden = layer(hidden, c)
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return self.norm_f(hidden)
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class Model(nn.Module):
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def __init__(self, args: ModelArgs):
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super().__init__()
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self.args = args
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self.model_type = args.model_type
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self.backbone = Mamba2(args)
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if not args.tie_word_embeddings:
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self.lm_head = nn.Linear(args.hidden_size, args.vocab_size, bias=False)
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def __call__(self, inputs: mx.array, cache=None):
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hidden = self.backbone(inputs, cache)
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if self.args.tie_word_embeddings:
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logits = self.backbone.embeddings.as_linear(hidden)
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else:
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logits = self.lm_head(hidden)
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return logits
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def sanitize(self, weights):
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for k, v in weights.items():
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if "conv1d.weight" in k and v.shape[-1] != 1:
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weights[k] = v.moveaxis(2, 1)
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return weights
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def make_cache(self):
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return [MambaCache() for _ in range(len(self.layers))]
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@property
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def layers(self):
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return self.backbone.layers |