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x_transformer.py
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x_transformer.py
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#===================================================================================================================
# X Trasformer Module
# Partial x-transformers code With useful modifications
#
# Version 1.0
#
# Original source code courtesy of lucidrains
# https://github.com/lucidrains/x-transformers
#
# Original source code retrieved on 05/10/2023
#
# Project Los Angeles
# Tegridy Code 2023
#===================================================================================================================
# Critical dependencies
#
# !pip install torch
# !pip install einops
#===================================================================================================================
from functools import partial
import torch
from torch import nn, einsum, Tensor
import torch.nn.functional as F
from collections import namedtuple
from functools import wraps
from packaging import version
from dataclasses import dataclass
from einops import rearrange
import math
from random import random
from functools import partial
from inspect import isfunction
from dataclasses import dataclass
from typing import List
from einops import rearrange, repeat, reduce
from einops.layers.torch import Rearrange
from math import ceil
from einops import rearrange, pack, unpack
#===================================================================================================================
# constants
EfficientAttentionConfig = namedtuple('EfficientAttentionConfig', ['enable_flash', 'enable_math', 'enable_mem_efficient'])
@dataclass
class Intermediates:
qk_similarities: Tensor = None
pre_softmax_attn: Tensor = None
post_softmax_attn: Tensor = None
# helpers
def exists(val):
return val is not None
def default(val, d):
return val if exists(val) else d
def once(fn):
called = False
@wraps(fn)
def inner(x):
nonlocal called
if called:
return
called = True
return fn(x)
return inner
print_once = once(print)
# main class
class Attend(nn.Module):
def __init__(
self,
*,
dropout = 0.,
causal = False,
heads = None,
talking_heads = False,
scale = None,
qk_norm = False,
flash = False,
):
super().__init__()
self.scale = scale
self.qk_norm = qk_norm
self.causal = causal
self.attn_fn = partial(F.softmax, dtype = torch.float32) if not qk_norm else F.softmax
self.dropout = dropout
self.attn_dropout = nn.Dropout(dropout)
# talking heads
assert not (flash and talking_heads), 'talking heads not compatible with flash attention'
self.talking_heads = talking_heads
if talking_heads:
self.pre_softmax_talking_heads = nn.Conv2d(heads, heads, 1, bias = False)
self.post_softmax_talking_heads = nn.Conv2d(heads, heads, 1, bias = False)
# flash attention
self.flash = flash
assert not (flash and version.parse(torch.__version__) < version.parse('2.0.0')), 'in order to use flash attention, you must be using pytorch 2.0 or above'
# determine efficient attention configs for cuda and cpu
self.cpu_config = EfficientAttentionConfig(True, True, True)
self.cuda_config = None
if not torch.cuda.is_available() or not flash:
return
device_properties = torch.cuda.get_device_properties(torch.device('cuda'))
if device_properties.major == 8 and device_properties.minor == 0:
print_once('A100 GPU detected, using flash attention if input tensor is on cuda')
self.cuda_config = EfficientAttentionConfig(True, False, False)
else:
print_once('Non-A100 GPU detected, using math or mem efficient attention if input tensor is on cuda')
self.cuda_config = EfficientAttentionConfig(False, True, True)
def flash_attn(
self,
q, k, v,
mask = None,
attn_bias = None
):
batch, heads, q_len, _, k_len, is_cuda, device = *q.shape, k.shape[-2], q.is_cuda, q.device
# Recommended for multi-query single-key-value attention by Tri Dao
# kv shape torch.Size([1, 512, 64]) -> torch.Size([1, 8, 512, 64])
if k.ndim == 3:
k = rearrange(k, 'b ... -> b 1 ...').expand_as(q)
if v.ndim == 3:
v = rearrange(v, 'b ... -> b 1 ...').expand_as(q)
# handle scale - by default they scale by dim_head ** -0.5, but need to take care if using cosine sim attention
if self.qk_norm:
default_scale = q.shape[-1] ** -0.5
q = q * (default_scale / self.scale)
# Check if mask exists and expand to compatible shape
# The mask is B L, so it would have to be expanded to B H N L
causal = self.causal
if exists(mask):
assert mask.ndim == 4
mask = mask.expand(batch, heads, q_len, k_len)
# manually handle causal mask, if another mask was given
if causal:
causal_mask = torch.ones((q_len, k_len), dtype = torch.bool, device = device).triu(k_len - q_len + 1)
mask = mask | causal_mask
causal = False
# handle alibi positional bias
# convert from bool to float
if exists(attn_bias):
attn_bias = rearrange(attn_bias, 'h i j -> 1 h i j').expand(batch, -1, -1, -1)
# if mask given, the mask would already contain the causal mask from above logic
# otherwise, if no mask given but still causal, mask out alibi positional bias to a large negative number
mask_value = -torch.finfo(q.dtype).max
if exists(mask):
attn_bias = attn_bias.masked_fill(mask, mask_value // 2)
elif causal:
causal_mask = torch.ones((q_len, k_len), dtype = torch.bool, device = device).triu(k_len - q_len + 1)
attn_bias = attn_bias.masked_fill(causal_mask, mask_value // 2)
causal = False
# scaled_dot_product_attention handles attn_mask either as bool or additive bias
# make it an additive bias here
mask = attn_bias
# Check if there is a compatible device for flash attention
config = self.cuda_config if is_cuda else self.cpu_config
# pytorch 2.0 flash attn: q, k, v, mask, dropout, causal, softmax_scale
with torch.backends.cuda.sdp_kernel(enable_math=True, enable_mem_efficient=True):
out = F.scaled_dot_product_attention(
q, k, v,
attn_mask = mask,
dropout_p = self.dropout if self.training else 0.,
is_causal = causal
)
return out, Intermediates()
def forward(
self,
q, k, v,
mask = None,
attn_bias = None,
prev_attn = None
):
"""
einstein notation
b - batch
h - heads
n, i, j - sequence length (base sequence length, source, target)
d - feature dimension
"""
n, device = q.shape[-2], q.device
scale = default(self.scale, q.shape[-1] ** -0.5)
if self.flash:
assert not exists(prev_attn), 'residual attention not compatible with flash attention'
return self.flash_attn(q, k, v, mask = mask, attn_bias = attn_bias)
kv_einsum_eq = 'b j d' if k.ndim == 3 else 'b h j d'
dots = einsum(f'b h i d, {kv_einsum_eq} -> b h i j', q, k) * scale
if exists(prev_attn):
dots = dots + prev_attn
qk_similarities = dots.clone()
if self.talking_heads:
dots = self.pre_softmax_talking_heads(dots)
if exists(attn_bias):
dots = dots + attn_bias
dtype = dots.dtype
pre_softmax_attn = dots.clone()
mask_value = -torch.finfo(dots.dtype).max
if exists(mask):
dots = dots.masked_fill(mask, mask_value)
if self.causal:
i, j = dots.shape[-2:]
causal_mask = torch.ones((i, j), dtype = torch.bool, device = device).triu(j - i + 1)
dots = dots.masked_fill(causal_mask, mask_value)
attn = self.attn_fn(dots, dim = -1)
attn = attn.type(dtype)
post_softmax_attn = attn.clone()
attn = self.attn_dropout(attn)
if self.talking_heads:
attn = self.post_softmax_talking_heads(attn)
out = einsum(f'b h i j, {kv_einsum_eq} -> b h i d', attn, v)
intermediates = Intermediates(
qk_similarities = qk_similarities,
pre_softmax_attn = pre_softmax_attn,
post_softmax_attn = post_softmax_attn
)
return out, intermediates
#===================================================================================================================
# constants
DEFAULT_DIM_HEAD = 64
@dataclass
class LayerIntermediates:
hiddens: List[Tensor] = None,
attn_intermediates: List[Intermediates] = None
# helpers
def exists(val):
return val is not None
def default(val, d):
if exists(val):
return val
return d() if isfunction(d) else d
def cast_tuple(val, depth):
return val if isinstance(val, tuple) else (val,) * depth
def maybe(fn):
@wraps(fn)
def inner(x, *args, **kwargs):
if not exists(x):
return x
return fn(x, *args, **kwargs)
return inner
class always():
def __init__(self, val):
self.val = val
def __call__(self, *args, **kwargs):
return self.val
class not_equals():
def __init__(self, val):
self.val = val
def __call__(self, x, *args, **kwargs):
return x != self.val
class equals():
def __init__(self, val):
self.val = val
def __call__(self, x, *args, **kwargs):
return x == self.val
# tensor helpers
def max_neg_value(tensor):
return -torch.finfo(tensor.dtype).max
def l2norm(t, groups = 1):
t = rearrange(t, '... (g d) -> ... g d', g = groups)
t = F.normalize(t, p = 2, dim = -1)
return rearrange(t, '... g d -> ... (g d)')
def pad_at_dim(t, pad, dim = -1, value = 0.):
dims_from_right = (- dim - 1) if dim < 0 else (t.ndim - dim - 1)
zeros = ((0, 0) * dims_from_right)
return F.pad(t, (*zeros, *pad), value = value)
def or_reduce(masks):
head, *body = masks
for rest in body:
head = head | rest
return head
# init helpers
def init_zero_(layer):
nn.init.constant_(layer.weight, 0.)
if exists(layer.bias):
nn.init.constant_(layer.bias, 0.)
# keyword argument helpers
def pick_and_pop(keys, d):
values = list(map(lambda key: d.pop(key), keys))
return dict(zip(keys, values))
def group_dict_by_key(cond, d):
return_val = [dict(),dict()]
for key in d.keys():
match = bool(cond(key))
ind = int(not match)
return_val[ind][key] = d[key]
return (*return_val,)
def string_begins_with(prefix, str):
return str.startswith(prefix)
def group_by_key_prefix(prefix, d):
return group_dict_by_key(partial(string_begins_with, prefix), d)
def groupby_prefix_and_trim(prefix, d):
kwargs_with_prefix, kwargs = group_dict_by_key(partial(string_begins_with, prefix), d)
kwargs_without_prefix = dict(map(lambda x: (x[0][len(prefix):], x[1]), tuple(kwargs_with_prefix.items())))
return kwargs_without_prefix, kwargs
# initializations
def deepnorm_init(
transformer,
beta,
module_name_match_list = ['.ff.', '.to_v', '.to_out']
):
for name, module in transformer.named_modules():
if type(module) != nn.Linear:
continue
needs_beta_gain = any(map(lambda substr: substr in name, module_name_match_list))
gain = beta if needs_beta_gain else 1
nn.init.xavier_normal_(module.weight.data, gain = gain)
if exists(module.bias):
nn.init.constant_(module.bias.data, 0)
# structured dropout, more effective than traditional attention dropouts
def dropout_seq(seq, mask, dropout):
b, n, *_, device = *seq.shape, seq.device
logits = torch.randn(b, n, device = device)
if exists(mask):
mask_value = max_neg_value(logits)
logits = logits.masked_fill(~mask, mask_value)
keep_prob = 1. - dropout
num_keep = max(1, int(keep_prob * n))
keep_indices = logits.topk(num_keep, dim = 1).indices
batch_indices = torch.arange(b, device = device)
batch_indices = rearrange(batch_indices, 'b -> b 1')
seq = seq[batch_indices, keep_indices]
if exists(mask):
seq_counts = mask.sum(dim = -1)
seq_keep_counts = torch.ceil(seq_counts * keep_prob).int()
keep_mask = torch.arange(num_keep, device = device) < rearrange(seq_keep_counts, 'b -> b 1')
mask = mask[batch_indices, keep_indices] & keep_mask
return seq, mask
# activations
class ReluSquared(nn.Module):
def forward(self, x):
return F.relu(x) ** 2
# embedding
class TokenEmbedding(nn.Module):
def __init__(self, dim, num_tokens, l2norm_embed = False):
super().__init__()
self.l2norm_embed = l2norm_embed
self.emb = nn.Embedding(num_tokens, dim)
def forward(self, x):
token_emb = self.emb(x)
return l2norm(token_emb) if self.l2norm_embed else token_emb
# positional embeddings
class AbsolutePositionalEmbedding(nn.Module):
def __init__(self, dim, max_seq_len, l2norm_embed = False):
super().__init__()
self.scale = dim ** -0.5 if not l2norm_embed else 1.
self.max_seq_len = max_seq_len
self.l2norm_embed = l2norm_embed
self.emb = nn.Embedding(max_seq_len, dim)
def forward(self, x, pos = None):
seq_len, device = x.shape[1], x.device
assert seq_len <= self.max_seq_len, f'you are passing in a sequence length of {seq_len} but your absolute positional embedding has a max sequence length of {self.max_seq_len}'
if not exists(pos):
pos = torch.arange(seq_len, device = device)
pos_emb = self.emb(pos)
pos_emb = pos_emb * self.scale
return l2norm(pos_emb) if self.l2norm_embed else pos_emb
class ScaledSinusoidalEmbedding(nn.Module):
def __init__(self, dim, theta = 10000):
super().__init__()
assert (dim % 2) == 0
self.scale = nn.Parameter(torch.ones(1) * dim ** -0.5)
half_dim = dim // 2
freq_seq = torch.arange(half_dim).float() / half_dim
inv_freq = theta ** -freq_seq
self.register_buffer('inv_freq', inv_freq, persistent = False)
def forward(self, x, pos = None):
seq_len, device = x.shape[1], x.device
if not exists(pos):
pos = torch.arange(seq_len, device = device)
emb = einsum('i, j -> i j', pos, self.inv_freq)
emb = torch.cat((emb.sin(), emb.cos()), dim = -1)
return emb * self.scale
class RelativePositionBias(nn.Module):
def __init__(self, scale, causal = False, num_buckets = 32, max_distance = 128, heads = 8):
super().__init__()
self.scale = scale
self.causal = causal
self.num_buckets = num_buckets
self.max_distance = max_distance
self.relative_attention_bias = nn.Embedding(num_buckets, heads)
@staticmethod
def _relative_position_bucket(relative_position, causal = True, num_buckets = 32, max_distance = 128):
ret = 0
n = -relative_position
if not causal:
num_buckets //= 2
ret += (n < 0).long() * num_buckets
n = torch.abs(n)
else:
n = torch.max(n, torch.zeros_like(n))
max_exact = num_buckets // 2
is_small = n < max_exact
val_if_large = max_exact + (
torch.log(n.float() / max_exact) / math.log(max_distance / max_exact) * (num_buckets - max_exact)
).long()
val_if_large = torch.min(val_if_large, torch.full_like(val_if_large, num_buckets - 1))
ret += torch.where(is_small, n, val_if_large)
return ret
@property
def device(self):
return next(self.parameters()).device
def forward(self, i, j):
device = self.device
q_pos = torch.arange(j - i, j, dtype = torch.long, device = device)
k_pos = torch.arange(j, dtype = torch.long, device = device)
rel_pos = k_pos[None, :] - q_pos[:, None]
rp_bucket = self._relative_position_bucket(rel_pos, causal = self.causal, num_buckets = self.num_buckets, max_distance = self.max_distance)
values = self.relative_attention_bias(rp_bucket)
bias = rearrange(values, 'i j h -> h i j')
return bias * self.scale
class DynamicPositionBias(nn.Module):
def __init__(self, dim, *, heads, depth, log_distance = False, norm = False):
super().__init__()
assert depth >= 1, 'depth for dynamic position bias MLP must be greater or equal to 1'
self.log_distance = log_distance
self.mlp = nn.ModuleList([])
self.mlp.append(nn.Sequential(
nn.Linear(1, dim),
nn.LayerNorm(dim) if norm else nn.Identity(),
nn.SiLU()
))
for _ in range(depth - 1):
self.mlp.append(nn.Sequential(
nn.Linear(dim, dim),
nn.LayerNorm(dim) if norm else nn.Identity(),
nn.SiLU()
))
self.mlp.append(nn.Linear(dim, heads))
@property
def device(self):
return next(self.parameters()).device
def forward(self, i, j):
assert i == j
n, device = j, self.device
# get the (n x n) matrix of distances
seq_arange = torch.arange(n, device = device)
context_arange = torch.arange(n, device = device)
indices = rearrange(seq_arange, 'i -> i 1') - rearrange(context_arange, 'j -> 1 j')
indices += (n - 1)
# input to continuous positions MLP
pos = torch.arange(-n + 1, n, device = device).float()
pos = rearrange(pos, '... -> ... 1')
if self.log_distance:
pos = torch.sign(pos) * torch.log(pos.abs() + 1) # log of distance is sign(rel_pos) * log(abs(rel_pos) + 1)
for layer in self.mlp:
pos = layer(pos)
# get position biases
bias = pos[indices]
bias = rearrange(bias, 'i j h -> h i j')
return bias
class AlibiPositionalBias(nn.Module):
def __init__(self, heads, total_heads, **kwargs):
super().__init__()
self.heads = heads
self.total_heads = total_heads
slopes = Tensor(self._get_slopes(heads))
slopes = rearrange(slopes, 'h -> h 1 1')
self.register_buffer('slopes', slopes, persistent = False)
self.register_buffer('bias', None, persistent = False)
def get_bias(self, i, j, device):
i_arange = torch.arange(j - i, j, device = device)
j_arange = torch.arange(j, device = device)
bias = -torch.abs(rearrange(j_arange, 'j -> 1 1 j') - rearrange(i_arange, 'i -> 1 i 1'))
return bias
@staticmethod
def _get_slopes(heads):
def get_slopes_power_of_2(n):
start = (2**(-2**-(math.log2(n)-3)))
ratio = start
return [start*ratio**i for i in range(n)]
if math.log2(heads).is_integer():
return get_slopes_power_of_2(heads)
closest_power_of_2 = 2 ** math.floor(math.log2(heads))
return get_slopes_power_of_2(closest_power_of_2) + get_slopes_power_of_2(2 * closest_power_of_2)[0::2][:heads-closest_power_of_2]
@property
def device(self):
return next(self.buffers()).device
def forward(self, i, j):
h, device = self.total_heads, self.device
if exists(self.bias) and self.bias.shape[-1] >= j:
return self.bias[..., :i, :j]
bias = self.get_bias(i, j, device)
bias = bias * self.slopes
num_heads_unalibied = h - bias.shape[0]
bias = pad_at_dim(bias, (0, num_heads_unalibied), dim = 0)
self.register_buffer('bias', bias, persistent = False)
return self.bias
class LearnedAlibiPositionalBias(AlibiPositionalBias):
def __init__(self, heads, total_heads):
super().__init__(heads, total_heads)
log_slopes = torch.log(self.slopes)
self.learned_logslopes = nn.Parameter(log_slopes)
def forward(self, i, j):
h, i, j, device = self.heads, self.device
def get_slopes(param):
return pad_at_dim(param.exp(), (0, h - param.shape[0]), dim = -2)
if exists(self.bias) and self.bias.shape[-1] >= j:
bias = self.bias[..., :i, :j]
else:
bias = self.get_bias(i, j, device)
self.register_buffer('bias', bias, persistent = False)
slopes = get_slopes(self.learned_logslopes)
bias = bias * slopes
return bias
class RotaryEmbedding(nn.Module):
def __init__(
self,
dim,
use_xpos = False,
scale_base = 512
):
super().__init__()
inv_freq = 1. / (10000 ** (torch.arange(0, dim, 2).float() / dim))
self.register_buffer('inv_freq', inv_freq)
if not use_xpos:
self.register_buffer('scale', None)
return
scale = (torch.arange(0, dim, 2) + 0.4 * dim) / (1.4 * dim)
self.scale_base = scale_base
self.register_buffer('scale', scale)
def forward(self, seq_len, device):
t = torch.arange(seq_len, device = device).type_as(self.inv_freq)
freqs = torch.einsum('i , j -> i j', t, self.inv_freq)
freqs = torch.cat((freqs, freqs), dim = -1)
if not exists(self.scale):
return freqs, 1.
power = (torch.arange(seq_len, device = device) - (seq_len // 2)) / self.scale_base
scale = self.scale ** rearrange(power, 'n -> n 1')
scale = torch.cat((scale, scale), dim = -1)
return freqs, scale
def rotate_half(x):
x = rearrange(x, '... (j d) -> ... j d', j = 2)
x1, x2 = x.unbind(dim = -2)
return torch.cat((-x2, x1), dim = -1)
def apply_rotary_pos_emb(t, freqs, scale = 1):
seq_len = t.shape[-2]
freqs = freqs[-seq_len:, :]
return (t * freqs.cos() * scale) + (rotate_half(t) * freqs.sin() * scale)
# norms
class Scale(nn.Module):
def __init__(self, value, fn):
super().__init__()
self.value = value
self.fn = fn
def forward(self, x, **kwargs):
out = self.fn(x, **kwargs)
scale_fn = lambda t: t * self.value
if not isinstance(out, tuple):
return scale_fn(out)
return (scale_fn(out[0]), *out[1:])
class ScaleNorm(nn.Module):
def __init__(self, dim, eps = 1e-5):
super().__init__()
self.eps = eps
self.g = nn.Parameter(torch.ones(1) * (dim ** -0.5))
def forward(self, x):
norm = torch.norm(x, dim = -1, keepdim = True)
return x / norm.clamp(min = self.eps) * self.g
class RMSNorm(nn.Module):
def __init__(self, dim, eps = 1e-8):
super().__init__()
self.scale = dim ** -0.5
self.eps = eps
self.g = nn.Parameter(torch.ones(dim))
def forward(self, x):
norm = torch.norm(x, dim = -1, keepdim = True) * self.scale
return x / norm.clamp(min = self.eps) * self.g
# residual and residual gates
class Residual(nn.Module):
def __init__(self, dim, scale_residual = False, scale_residual_constant = 1.):
super().__init__()
self.residual_scale = nn.Parameter(torch.ones(dim)) if scale_residual else None
self.scale_residual_constant = scale_residual_constant
def forward(self, x, residual):
if exists(self.residual_scale):
residual = residual * self.residual_scale
if self.scale_residual_constant != 1:
residual = residual * self.scale_residual_constant
return x + residual
class GRUGating(nn.Module):
def __init__(self, dim, scale_residual = False, **kwargs):
super().__init__()
self.gru = nn.GRUCell(dim, dim)
self.residual_scale = nn.Parameter(torch.ones(dim)) if scale_residual else None
def forward(self, x, residual):
if exists(self.residual_scale):
residual = residual * self.residual_scale
gated_output = self.gru(
rearrange(x, 'b n d -> (b n) d'),
rearrange(residual, 'b n d -> (b n) d')
)
return gated_output.reshape_as(x)
# token shifting
def shift(t, amount, mask = None):
if amount == 0:
return t
else:
amount = min(amount, t.shape[1])
if exists(mask):
t = t.masked_fill(~mask[..., None], 0.)
return pad_at_dim(t, (amount, -amount), dim = - 2, value = 0.)
class ShiftTokens(nn.Module):
def __init__(self, shifts, fn):
super().__init__()
self.fn = fn
self.shifts = tuple(shifts)
def forward(self, x, **kwargs):
mask = kwargs.get('mask', None)
shifts = self.shifts
segments = len(shifts)
feats_per_shift = x.shape[-1] // segments
splitted = x.split(feats_per_shift, dim = -1)
segments_to_shift, rest = splitted[:segments], splitted[segments:]
segments_to_shift = list(map(lambda args: shift(*args, mask = mask), zip(segments_to_shift, shifts)))
x = torch.cat((*segments_to_shift, *rest), dim = -1)
return self.fn(x, **kwargs)
# feedforward
class GLU(nn.Module):
def __init__(self, dim_in, dim_out, activation):
super().__init__()
self.act = activation
self.proj = nn.Linear(dim_in, dim_out * 2)
def forward(self, x):
x, gate = self.proj(x).chunk(2, dim = -1)
return x * self.act(gate)
class FeedForward(nn.Module):
def __init__(
self,
dim,
dim_out = None,
mult = 4,
glu = False,
swish = False,
relu_squared = False,
post_act_ln = False,
dropout = 0.,
no_bias = False,
zero_init_output = False
):
super().__init__()
inner_dim = int(dim * mult)
dim_out = default(dim_out, dim)
if relu_squared:
activation = ReluSquared()
elif swish:
activation = nn.SiLU()
else:
activation = nn.GELU()
project_in = nn.Sequential(
nn.Linear(dim, inner_dim, bias = not no_bias),
activation
) if not glu else GLU(dim, inner_dim, activation)
self.ff = nn.Sequential(
project_in,
nn.LayerNorm(inner_dim) if post_act_ln else nn.Identity(),
nn.Dropout(dropout),
nn.Linear(inner_dim, dim_out, bias = not no_bias)
)
# init last linear layer to 0
if zero_init_output:
init_zero_(self.ff[-1])
def forward(self, x):
return self.ff(x)
# attention. it is all we need
class Attention(nn.Module):
def __init__(
self,
dim,
dim_head = DEFAULT_DIM_HEAD,
heads = 8,
causal = False,
flash = False,
talking_heads = False,
head_scale = False,
sparse_topk = None,
num_mem_kv = 0,
dropout = 0.,
on_attn = False,
gate_values = False,
zero_init_output = False,
max_attend_past = None,
qk_norm = False,
qk_norm_groups = 1,
qk_norm_scale = 10,
qk_norm_dim_scale = False,
one_kv_head = False,
shared_kv = False,
value_dim_head = None,
tensor_product = False # https://arxiv.org/abs/2208.06061
):
super().__init__()
self.scale = dim_head ** -0.5
self.heads = heads
self.causal = causal
self.max_attend_past = max_attend_past
value_dim_head = default(value_dim_head, dim_head)
q_dim = k_dim = dim_head * heads
v_dim = out_dim = value_dim_head * heads
self.one_kv_head = one_kv_head
if one_kv_head:
k_dim = dim_head
v_dim = value_dim_head
out_dim = v_dim * heads
self.to_q = nn.Linear(dim, q_dim, bias = False)
self.to_k = nn.Linear(dim, k_dim, bias = False)
# shared key / values, for further memory savings during inference
assert not (shared_kv and value_dim_head != dim_head), 'key and value head dimensions must be equal for shared key / values'
self.to_v = nn.Linear(dim, v_dim, bias = False) if not shared_kv else None
# relations projection from tp-attention
self.to_r = nn.Linear(dim, v_dim, bias = False) if tensor_product else None
# add GLU gating for aggregated values, from alphafold2
self.to_v_gate = None
if gate_values:
self.to_v_gate = nn.Linear(dim, out_dim)
nn.init.constant_(self.to_v_gate.weight, 0)
nn.init.constant_(self.to_v_gate.bias, 1)
# cosine sim attention
self.qk_norm = qk_norm
self.qk_norm_groups = qk_norm_groups
self.qk_norm_scale = qk_norm_scale
# whether to use the rmsnorm (equivalent to cosine sim attention when scale is equal to 1) - https://arxiv.org/abs/2302.05442
self.qk_norm_dim_scale = qk_norm_dim_scale
self.qk_norm_q_scale = self.qk_norm_k_scale = 1
if qk_norm and qk_norm_dim_scale:
self.qk_norm_q_scale = nn.Parameter(torch.ones(dim_head))
self.qk_norm_k_scale = nn.Parameter(torch.ones(dim_head))
assert (not qk_norm) or (dim_head % qk_norm_groups) == 0, 'dimension per attention head must be divisible by the qk norm groups'
assert not (qk_norm and (dim_head // qk_norm_groups) <= 2), 'the group dimension may be too small (2 was too small in my tests, but 4 still works, surprisingly)'
# attend class - includes core attention algorithm + talking heads
self.attend = Attend(
heads = heads,
causal = causal,
talking_heads = talking_heads,
dropout = dropout,
qk_norm = qk_norm,
scale = qk_norm_scale if qk_norm else self.scale,
flash = flash
)
# head scaling
self.head_scale = head_scale
if head_scale:
self.head_scale_params = nn.Parameter(torch.ones(1, heads, 1, 1))
# explicit topk sparse attention
self.sparse_topk = sparse_topk
# add memory key / values
self.num_mem_kv = num_mem_kv
if num_mem_kv > 0:
self.mem_k = nn.Parameter(torch.randn(heads, num_mem_kv, dim_head))
self.mem_v = nn.Parameter(torch.randn(heads, num_mem_kv, dim_head))
# attention on attention
self.attn_on_attn = on_attn
self.to_out = nn.Sequential(nn.Linear(out_dim, dim * 2, bias = False), nn.GLU()) if on_attn else nn.Linear(out_dim, dim, bias = False)
# init output projection 0
if zero_init_output:
init_zero_(self.to_out)
def forward(
self,
x,
context = None,
mask = None,
context_mask = None,
attn_mask = None,
rel_pos = None,
rotary_pos_emb = None,
prev_attn = None,
mem = None
):
b, n, _, h, head_scale, device, has_context = *x.shape, self.heads, self.head_scale, x.device, exists(context)
kv_input = default(context, x)
q_input = x
k_input = kv_input
v_input = kv_input