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# Copyright (c) 2023, Tri Dao, Albert Gu.
import math
from typing import Optional
import torch
import torch.nn as nn
import torch.nn.functional as F
from torch import Tensor
from einops import rearrange, repeat
from mamba_ssm.ops.selective_scan_interface import selective_scan_fn, mamba_inner_fn
try:
from causal_conv1d import causal_conv1d_fn, causal_conv1d_update
except ImportError:
causal_conv1d_fn, causal_conv1d_update = None, None
try:
from mamba_ssm.ops.triton.selective_state_update import selective_state_update
except ImportError:
selective_state_update = None
try:
from mamba_ssm.ops.triton.layer_norm import RMSNorm, layer_norm_fn, rms_norm_fn
except ImportError:
RMSNorm, layer_norm_fn, rms_norm_fn = None, None, None
class Mamba(nn.Module):
def __init__(
self,
d_model,
d_state=16,
d_conv=4,
expand=2,
dt_rank="auto",
dt_min=0.001,
dt_max=0.1,
dt_init="random",
dt_scale=1.0,
dt_init_floor=1e-4,
conv_bias=True,
bias=False,
use_fast_path=True, # Fused kernel options
layer_idx=None,
device=None,
dtype=None,
):
factory_kwargs = {"device": device, "dtype": dtype}
super().__init__()
self.d_model = d_model
self.d_state = d_state
self.d_conv = d_conv
self.expand = expand
self.d_inner = int(self.expand * self.d_model)
self.dt_rank = math.ceil(self.d_model / 16) if dt_rank == "auto" else dt_rank
self.use_fast_path = use_fast_path
self.layer_idx = layer_idx
self.in_proj = nn.Linear(self.d_model, self.d_inner * 2, bias=bias, **factory_kwargs)
self.conv1d = nn.Conv1d(
in_channels=self.d_inner,
out_channels=self.d_inner,
bias=conv_bias,
kernel_size=d_conv,
groups=self.d_inner,
padding=d_conv - 1,
**factory_kwargs,
)
self.activation = "silu"
self.act = nn.SiLU()
self.x_proj = nn.Linear(
self.d_inner, self.dt_rank + self.d_state * 2, bias=False, **factory_kwargs
)
self.dt_proj = nn.Linear(self.dt_rank, self.d_inner, bias=True, **factory_kwargs)
# Initialize special dt projection to preserve variance at initialization
dt_init_std = self.dt_rank**-0.5 * dt_scale
if dt_init == "constant":
nn.init.constant_(self.dt_proj.weight, dt_init_std)
elif dt_init == "random":
nn.init.uniform_(self.dt_proj.weight, -dt_init_std, dt_init_std)
else:
raise NotImplementedError
# Initialize dt bias so that F.softplus(dt_bias) is between dt_min and dt_max
dt = torch.exp(
torch.rand(self.d_inner, **factory_kwargs) * (math.log(dt_max) - math.log(dt_min))
+ math.log(dt_min)
).clamp(min=dt_init_floor)
# Inverse of softplus: https://github.com/pytorch/pytorch/issues/72759
inv_dt = dt + torch.log(-torch.expm1(-dt))
with torch.no_grad():
self.dt_proj.bias.copy_(inv_dt)
# Our initialization would set all Linear.bias to zero, need to mark this one as _no_reinit
self.dt_proj.bias._no_reinit = True
# S4D real initialization
A = repeat(
torch.arange(1, self.d_state + 1, dtype=torch.float32, device=device),
"n -> d n",
d=self.d_inner,
).contiguous()
A_log = torch.log(A) # Keep A_log in fp32
self.A_log = nn.Parameter(A_log)
self.A_log._no_weight_decay = True
# D "skip" parameter
self.D = nn.Parameter(torch.ones(self.d_inner, device=device)) # Keep in fp32
self.D._no_weight_decay = True
self.out_proj = nn.Linear(self.d_inner, self.d_model, bias=bias, **factory_kwargs)
def forward(self, hidden_states, inference_params=None):
"""
hidden_states: (B, L, D)
Returns: same shape as hidden_states
"""
batch, seqlen, dim = hidden_states.shape
conv_state, ssm_state = None, None
if inference_params is not None:
conv_state, ssm_state = self._get_states_from_cache(inference_params, batch)
if inference_params.seqlen_offset > 0:
# The states are updated inplace
out, _, _ = self.step(hidden_states, conv_state, ssm_state)
return out
# We do matmul and transpose BLH -> HBL at the same time
xz = rearrange(
self.in_proj.weight @ rearrange(hidden_states, "b l d -> d (b l)"),
"d (b l) -> b d l",
l=seqlen,
)
if self.in_proj.bias is not None:
xz = xz + rearrange(self.in_proj.bias.to(dtype=xz.dtype), "d -> d 1")
A = -torch.exp(self.A_log.float()) # (d_inner, d_state)
# In the backward pass we write dx and dz next to each other to avoid torch.cat
if self.use_fast_path and causal_conv1d_fn is not None and inference_params is None: # Doesn't support outputting the states
out = mamba_inner_fn(
xz,
self.conv1d.weight,
self.conv1d.bias,
self.x_proj.weight,
self.dt_proj.weight,
self.out_proj.weight,
self.out_proj.bias,
A,
None, # input-dependent B
None, # input-dependent C
self.D.float(),
delta_bias=self.dt_proj.bias.float(),
delta_softplus=True,
)
else:
x, z = xz.chunk(2, dim=1)
# Compute short convolution
if conv_state is not None:
# If we just take x[:, :, -self.d_conv :], it will error if seqlen < self.d_conv
# Instead F.pad will pad with zeros if seqlen < self.d_conv, and truncate otherwise.
conv_state.copy_(F.pad(x, (self.d_conv - x.shape[-1], 0))) # Update state (B D W)
if causal_conv1d_fn is None:
x = self.act(self.conv1d(x)[..., :seqlen])
else:
assert self.activation in ["silu", "swish"]
x = causal_conv1d_fn(
x=x,
weight=rearrange(self.conv1d.weight, "d 1 w -> d w"),
bias=self.conv1d.bias,
activation=self.activation,
)
# We're careful here about the layout, to avoid extra transposes.
# We want dt to have d as the slowest moving dimension
# and L as the fastest moving dimension, since those are what the ssm_scan kernel expects.
x_dbl = self.x_proj(rearrange(x, "b d l -> (b l) d")) # (bl d)
dt, B, C = torch.split(x_dbl, [self.dt_rank, self.d_state, self.d_state], dim=-1)
dt = self.dt_proj.weight @ dt.t()
dt = rearrange(dt, "d (b l) -> b d l", l=seqlen)
B = rearrange(B, "(b l) dstate -> b dstate l", l=seqlen).contiguous()
C = rearrange(C, "(b l) dstate -> b dstate l", l=seqlen).contiguous()
assert self.activation in ["silu", "swish"]
y = selective_scan_fn(
x,
dt,
A,
B,
C,
self.D.float(),
z=z,
delta_bias=self.dt_proj.bias.float(),
delta_softplus=True,
return_last_state=ssm_state is not None,
)
if ssm_state is not None:
y, last_state = y
ssm_state.copy_(last_state)
y = rearrange(y, "b d l -> b l d")
out = self.out_proj(y)
return out
def step(self, hidden_states, conv_state, ssm_state):
dtype = hidden_states.dtype
assert hidden_states.shape[1] == 1, "Only support decoding with 1 token at a time for now"
xz = self.in_proj(hidden_states.squeeze(1)) # (B 2D)
x, z = xz.chunk(2, dim=-1) # (B D)
# Conv step
if causal_conv1d_update is None:
conv_state.copy_(torch.roll(conv_state, shifts=-1, dims=-1)) # Update state (B D W)
conv_state[:, :, -1] = x
x = torch.sum(conv_state * rearrange(self.conv1d.weight, "d 1 w -> d w"), dim=-1) # (B D)
if self.conv1d.bias is not None:
x = x + self.conv1d.bias
x = self.act(x).to(dtype=dtype)
else:
x = causal_conv1d_update(
x,
conv_state,
rearrange(self.conv1d.weight, "d 1 w -> d w"),
self.conv1d.bias,
self.activation,
)
x_db = self.x_proj(x) # (B dt_rank+2*d_state)
dt, B, C = torch.split(x_db, [self.dt_rank, self.d_state, self.d_state], dim=-1)
# Don't add dt_bias here
dt = F.linear(dt, self.dt_proj.weight) # (B d_inner)
A = -torch.exp(self.A_log.float()) # (d_inner, d_state)
# SSM step
if selective_state_update is None:
# Discretize A and B
dt = F.softplus(dt + self.dt_proj.bias.to(dtype=dt.dtype))
dA = torch.exp(torch.einsum("bd,dn->bdn", dt, A))
dB = torch.einsum("bd,bn->bdn", dt, B)
ssm_state.copy_(ssm_state * dA + rearrange(x, "b d -> b d 1") * dB)
y = torch.einsum("bdn,bn->bd", ssm_state.to(dtype), C)
y = y + self.D.to(dtype) * x
y = y * self.act(z) # (B D)
else:
y = selective_state_update(
ssm_state, x, dt, A, B, C, self.D, z=z, dt_bias=self.dt_proj.bias, dt_softplus=True
)
out = self.out_proj(y)
return out.unsqueeze(1), conv_state, ssm_state
def allocate_inference_cache(self, batch_size, max_seqlen, dtype=None, **kwargs):
device = self.out_proj.weight.device
conv_dtype = self.conv1d.weight.dtype if dtype is None else dtype
conv_state = torch.zeros(
batch_size, self.d_model * self.expand, self.d_conv, device=device, dtype=conv_dtype
)
ssm_dtype = self.dt_proj.weight.dtype if dtype is None else dtype
# ssm_dtype = torch.float32
ssm_state = torch.zeros(
batch_size, self.d_model * self.expand, self.d_state, device=device, dtype=ssm_dtype
)
return conv_state, ssm_state
def _get_states_from_cache(self, inference_params, batch_size, initialize_states=False):
assert self.layer_idx is not None
if self.layer_idx not in inference_params.key_value_memory_dict:
batch_shape = (batch_size,)
conv_state = torch.zeros(
batch_size,
self.d_model * self.expand,
self.d_conv,
device=self.conv1d.weight.device,
dtype=self.conv1d.weight.dtype,
)
ssm_state = torch.zeros(
batch_size,
self.d_model * self.expand,
self.d_state,
device=self.dt_proj.weight.device,
dtype=self.dt_proj.weight.dtype,
# dtype=torch.float32,
)
inference_params.key_value_memory_dict[self.layer_idx] = (conv_state, ssm_state)
else:
conv_state, ssm_state = inference_params.key_value_memory_dict[self.layer_idx]
# TODO: What if batch size changes between generation, and we reuse the same states?
if initialize_states:
conv_state.zero_()
ssm_state.zero_()
return conv_state, ssm_state
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