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modeling_flax_longt5.py
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modeling_flax_longt5.py
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# coding=utf-8
# Copyright 2022 LongT5 Authors and HuggingFace Inc. team.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
""" Flax LongT5 model."""
import copy
from typing import Any, Callable, List, Optional, Tuple
import flax.linen as nn
import jax
import jax.numpy as jnp
import numpy as np
from flax.core.frozen_dict import FrozenDict, freeze, unfreeze
from flax.linen import combine_masks, make_causal_mask
from flax.linen import partitioning as nn_partitioning
from flax.linen.attention import dot_product_attention_weights
from flax.traverse_util import flatten_dict, unflatten_dict
from jax.random import PRNGKey
from ...modeling_flax_outputs import (
FlaxBaseModelOutput,
FlaxBaseModelOutputWithPastAndCrossAttentions,
FlaxCausalLMOutputWithCrossAttentions,
FlaxSeq2SeqLMOutput,
FlaxSeq2SeqModelOutput,
)
from ...modeling_flax_utils import (
ACT2FN,
FlaxPreTrainedModel,
append_call_sample_docstring,
append_replace_return_docstrings,
overwrite_call_docstring,
)
from ...utils import add_start_docstrings, add_start_docstrings_to_model_forward, logging, replace_return_docstrings
from .configuration_longt5 import LongT5Config
logger = logging.get_logger(__name__)
_CHECKPOINT_FOR_DOC = "google/long-t5-local-base"
_CONFIG_FOR_DOC = "LongT5Config"
remat = nn_partitioning.remat
# Copied from transformers.models.bart.modeling_flax_bart.shift_tokens_right
def shift_tokens_right(input_ids: np.array, pad_token_id: int, decoder_start_token_id: int) -> np.ndarray:
"""
Shift input ids one token to the right.
"""
shifted_input_ids = np.zeros_like(input_ids)
shifted_input_ids[:, 1:] = input_ids[:, :-1]
shifted_input_ids[:, 0] = decoder_start_token_id
shifted_input_ids = np.where(shifted_input_ids == -100, pad_token_id, shifted_input_ids)
return shifted_input_ids
def _pad_to_multiple(x: jnp.ndarray, block_len: int, axis: int, pad_value: int = 0) -> jnp.ndarray:
"""Pad an array so that a sequence length will be a multiple of `block_len`"""
pad_len = -x.shape[axis] % block_len
pad = [(0, 0)] * x.ndim
pad[axis] = (0, pad_len)
x = jnp.pad(x, pad_width=pad, mode="constant", constant_values=pad_value)
return x
def _split_into_blocks(x: jnp.ndarray, block_len: int, axis: int) -> jnp.ndarray:
"""Split an input array into blocks of a given `block_len` along the given `axis`. If the dimension length
is not a multiple of `block_len`, it will be padded first with selected `pad_value`.
"""
# pad tensor to multiple of block_len
if x.shape[axis] % block_len != 0:
x = _pad_to_multiple(x, block_len, axis, pad_value=0)
num_blocks = x.shape[axis] // block_len
output_shape = x.shape[:axis] + (num_blocks, block_len) + x.shape[(axis + 1) :]
return x.reshape(output_shape)
def _concatenate_3_blocks(x: jnp.ndarray, block_axis: int, sequence_axis: int, pad_value: int = 0) -> jnp.ndarray:
"""Concatenate three consecutive blocks for each input block for local attentiont.
For more information, see: https://arxiv.org/pdf/2112.07916.pdf.
"""
num_blocks = x.shape[block_axis]
pad = [(0, 0)] * x.ndim
pad[block_axis] = (1, 1)
# [batch_size, num_blocks, block_len] -> [batch_size, num_blocks + 2, block_len]
x = jnp.pad(x, pad_width=pad, mode="constant", constant_values=pad_value)
blocks_list: List[np.array] = []
for i in range(3):
# We use indexing approach here:
# https://numpy.org/doc/stable/user/basics.indexing.html#dealing-with-variable-numbers-of-indices-within-programs
indices = [slice(0, None)] * x.ndim
indices[block_axis] = slice(i, i + num_blocks)
indices = tuple(indices)
blocks_list.append(x[indices])
return jnp.concatenate(blocks_list, axis=sequence_axis) # [batch_size, num_blocks, 3 * block_len, ...]
def _make_3block_relative_position_ids(block_len: int) -> jnp.ndarray:
"""Makes 3-blocked relative position ids for local attention."""
position_ids = jnp.arange(3 * block_len, dtype=jnp.int32)
center_position_ids = position_ids[block_len:-block_len]
relative_position_ids = position_ids[None, :] - center_position_ids[:, None] # [block_len, 3 * block_len]
return relative_position_ids
def _mask_local_attention_mask(local_attention_mask: np.ndarray, block_len: int) -> jnp.ndarray:
"""Mask local attention mask to enforce that tokens are not allowed to attend tokens farther than ``local_radius."""
relative_position_ids = _make_3block_relative_position_ids(block_len)
locality_mask = jnp.abs(relative_position_ids) < block_len
locality_mask = locality_mask[None, None, :, :]
return jnp.logical_and(local_attention_mask, locality_mask)
def _get_local_attention_mask(attention_mask: np.ndarray, block_len: int) -> jnp.ndarray:
"""Prepare attention mask to be applied for a local attention."""
# [batch_size, num_blocks, block_len]
_blocked_attention_mask = _split_into_blocks(attention_mask, block_len, axis=1)
# [batch_size, num_block, 3 * block_len]
_3blocked_attention_mask = _concatenate_3_blocks(_blocked_attention_mask, block_axis=1, sequence_axis=2)
_blocked_attention_mask = _blocked_attention_mask[..., None]
_3blocked_attention_mask = _3blocked_attention_mask[..., None, :]
# [batch_size, num_block, block_len, 3 * block_len]
local_attention_mask = jnp.logical_and(_blocked_attention_mask, _3blocked_attention_mask)
local_attention_mask = _mask_local_attention_mask(local_attention_mask, block_len)
# [batch_size, 1, num_block, block_len, 3 * block_len]
return local_attention_mask[:, None, ...]
def _make_global_fixed_block_ids(attention_mask: np.ndarray, global_block_size: int) -> Tuple[jnp.ndarray, np.ndarray]:
"""Obtain the "fixed block" global id corresponding to each input token.
This implementation is a simlified version of the original Flaxformr implementation adopted from:
https://github.com/google/flaxformer/blob/main/flaxformer/architectures/longt5/long_attention.py.
In our scenario, as we use this strategy only for a decoder, orphan tokens, i.e. those tokens which do not make for
the whole fixed block, are assigned to the preceding block.
Padding tokens from the original sequence are represented by -1.
"""
batch_size, seq_len = attention_mask.shape[:2]
def handle_orphan_tokens(block_ids: np.ndarray) -> jnp.ndarray:
block_ends = (jnp.arange(seq_len) % global_block_size) == global_block_size - 1
true_block_ends = jnp.logical_and(block_ends, block_ids >= 0)
full_blocks = true_block_ends.sum(-1)[..., None]
block_ids = jnp.minimum(block_ids, full_blocks - 1)
return block_ids
fixed_block_mask = jnp.ones_like(attention_mask) / global_block_size
fixed_block_mask = jnp.cumsum(fixed_block_mask, axis=1) - fixed_block_mask
mask = jnp.where(attention_mask != 0.0, 1.0, -1000.0)
global_block_ids = jnp.maximum(
jnp.floor(mask + fixed_block_mask - 1.0), jnp.array(-1.0, dtype=attention_mask.dtype)
)
# set padding tokens to -1
global_block_ids = (global_block_ids * attention_mask) + (attention_mask - 1)
# [batch_size, seq_len]
global_block_ids = handle_orphan_tokens(global_block_ids)
num_globals = seq_len // global_block_size
# [batch_size, seq_len // global_block_size]
if num_globals > 0:
_sequence_block_ids_max = jnp.repeat(global_block_ids.max(axis=-1)[:, None], repeats=num_globals, axis=1)
else:
_sequence_block_ids_max = jnp.zeros((batch_size, 0), dtype=global_block_ids.dtype)
global_segment_ids = jnp.cumsum(jnp.ones((batch_size, num_globals)), axis=-1) - 1
global_segment_ids = jnp.where(global_segment_ids <= _sequence_block_ids_max, 1, 0)
return global_block_ids, global_segment_ids
def _make_side_relative_position_ids(attention_mask: np.ndarray, global_block_size: int) -> np.ndarray:
"""Create the relative position tensor for local -> global attention."""
block_ids, global_segment_ids = _make_global_fixed_block_ids(attention_mask, global_block_size)
global_seq_len = global_segment_ids.shape[-1]
global_positions = jnp.arange(global_seq_len)
side_relative_position = global_positions - block_ids[..., None]
return side_relative_position
def _create_global_aggregates(hidden_states: np.ndarray, block_ids: np.ndarray, global_seq_len: int) -> np.ndarray:
"""Compute individual block aggregates by summing over individual blocks."""
# (batch..., seq_len, global_seq_len))
one_hot_block_ids = jax.nn.one_hot(block_ids, global_seq_len)
return jnp.einsum("...nd,...ng->...gd", hidden_states, one_hot_block_ids)
# Copied from transformers.models.t5.modeling_flax_t5.FlaxT5LayerNorm with T5->LongT5
class FlaxLongT5LayerNorm(nn.Module):
hidden_size: int
dtype: jnp.dtype = jnp.float32
eps: float = 1e-6
weight_init: Callable[..., np.ndarray] = jax.nn.initializers.ones
def setup(self):
self.weight = self.param("weight", self.weight_init, (self.hidden_size,))
def __call__(self, hidden_states):
"""
Construct a layernorm module in the LongT5 style; No bias and no subtraction of mean.
"""
# layer norm should always be calculated in float32
variance = jnp.power(hidden_states.astype("f4"), 2).mean(axis=-1, keepdims=True)
hidden_states = hidden_states / jnp.sqrt(variance + self.eps)
return self.weight * hidden_states
# Copied from transformers.models.t5.modeling_flax_t5.FlaxT5DenseActDense with T5->LongT5
class FlaxLongT5DenseActDense(nn.Module):
config: LongT5Config
dtype: jnp.dtype = jnp.float32
def setup(self):
wi_init_std = self.config.initializer_factor * (self.config.d_model**-0.5)
wo_init_std = self.config.initializer_factor * (self.config.d_ff**-0.5)
self.wi = nn.Dense(
self.config.d_ff,
use_bias=False,
kernel_init=jax.nn.initializers.normal(wi_init_std),
dtype=self.dtype,
)
self.wo = nn.Dense(
self.config.d_model,
use_bias=False,
kernel_init=jax.nn.initializers.normal(wo_init_std),
dtype=self.dtype,
)
self.dropout = nn.Dropout(self.config.dropout_rate)
self.act = ACT2FN[self.config.dense_act_fn]
def __call__(self, hidden_states, deterministic=True):
hidden_states = self.wi(hidden_states)
hidden_states = self.act(hidden_states)
hidden_states = self.dropout(hidden_states, deterministic=deterministic)
hidden_states = self.wo(hidden_states)
return hidden_states
# Copied from transformers.models.t5.modeling_flax_t5.FlaxT5DenseGatedActDense with T5->LongT5
class FlaxLongT5DenseGatedActDense(nn.Module):
config: LongT5Config
dtype: jnp.dtype = jnp.float32 # the dtype of the computation
def setup(self):
wi_init_std = self.config.initializer_factor * (self.config.d_model**-0.5)
wo_init_std = self.config.initializer_factor * (self.config.d_ff**-0.5)
self.wi_0 = nn.Dense(
self.config.d_ff,
use_bias=False,
kernel_init=jax.nn.initializers.normal(wi_init_std),
dtype=self.dtype,
)
self.wi_1 = nn.Dense(
self.config.d_ff,
use_bias=False,
kernel_init=jax.nn.initializers.normal(wi_init_std),
dtype=self.dtype,
)
self.wo = nn.Dense(
self.config.d_model,
use_bias=False,
kernel_init=jax.nn.initializers.normal(wo_init_std),
dtype=self.dtype,
)
self.dropout = nn.Dropout(self.config.dropout_rate)
self.act = ACT2FN[self.config.dense_act_fn]
def __call__(self, hidden_states, deterministic):
hidden_gelu = self.act(self.wi_0(hidden_states))
hidden_linear = self.wi_1(hidden_states)
hidden_states = hidden_gelu * hidden_linear
hidden_states = self.dropout(hidden_states, deterministic=deterministic)
hidden_states = self.wo(hidden_states)
return hidden_states
# Copied from transformers.models.t5.modeling_flax_t5.FlaxT5LayerFF with T5->LongT5
class FlaxLongT5LayerFF(nn.Module):
config: LongT5Config
dtype: jnp.dtype = jnp.float32 # the dtype of the computation
def setup(self):
if self.config.is_gated_act:
self.DenseReluDense = FlaxLongT5DenseGatedActDense(self.config, dtype=self.dtype)
else:
self.DenseReluDense = FlaxLongT5DenseActDense(self.config, dtype=self.dtype)
self.layer_norm = FlaxLongT5LayerNorm(
self.config.d_model, eps=self.config.layer_norm_epsilon, dtype=self.dtype
)
self.dropout = nn.Dropout(self.config.dropout_rate)
def __call__(self, hidden_states, deterministic=True):
forwarded_states = self.layer_norm(hidden_states)
forwarded_states = self.DenseReluDense(forwarded_states, deterministic=deterministic)
hidden_states = hidden_states + self.dropout(forwarded_states, deterministic=deterministic)
return hidden_states
# Copied from transformers.models.t5.modeling_flax_t5.FlaxT5Attention with T5->LongT5
class FlaxLongT5Attention(nn.Module):
config: LongT5Config
has_relative_attention_bias: bool = False
causal: bool = False
dtype: jnp.dtype = jnp.float32 # the dtype of the computation
def setup(self):
self.relative_attention_num_buckets = self.config.relative_attention_num_buckets
self.relative_attention_max_distance = self.config.relative_attention_max_distance
self.d_model = self.config.d_model
self.key_value_proj_dim = self.config.d_kv
self.n_heads = self.config.num_heads
self.dropout = self.config.dropout_rate
self.inner_dim = self.n_heads * self.key_value_proj_dim
q_init_std = self.config.initializer_factor * ((self.inner_dim * self.key_value_proj_dim) ** -0.5)
kv_init_std = self.config.initializer_factor * (self.inner_dim**-0.5)
o_init_std = self.config.initializer_factor * (self.inner_dim**-0.5)
self.q = nn.Dense(
self.inner_dim,
use_bias=False,
kernel_init=jax.nn.initializers.normal(q_init_std),
dtype=self.dtype,
)
self.k = nn.Dense(
self.inner_dim,
use_bias=False,
kernel_init=jax.nn.initializers.normal(kv_init_std),
dtype=self.dtype,
)
self.v = nn.Dense(
self.inner_dim,
use_bias=False,
kernel_init=jax.nn.initializers.normal(kv_init_std),
dtype=self.dtype,
)
self.o = nn.Dense(
self.d_model,
use_bias=False,
kernel_init=jax.nn.initializers.normal(o_init_std),
dtype=self.dtype,
)
if self.has_relative_attention_bias:
self.relative_attention_bias = nn.Embed(
self.relative_attention_num_buckets,
self.n_heads,
embedding_init=jax.nn.initializers.normal(kv_init_std),
dtype=self.dtype,
)
@staticmethod
def _relative_position_bucket(relative_position, bidirectional=True, num_buckets=32, max_distance=128):
"""
Adapted from Mesh Tensorflow:
https://github.com/tensorflow/mesh/blob/0cb87fe07da627bf0b7e60475d59f95ed6b5be3d/mesh_tensorflow/transformer/transformer_layers.py#L593
Translate relative position to a bucket number for relative attention. The relative position is defined as
memory_position - query_position, i.e. the distance in tokens from the attending position to the attended-to
position. If bidirectional=False, then positive relative positions are invalid. We use smaller buckets for
small absolute relative_position and larger buckets for larger absolute relative_positions. All relative
positions >=max_distance map to the same bucket. All relative positions <=-max_distance map to the same bucket.
This should allow for more graceful generalization to longer sequences than the model has been trained on
"""
relative_buckets = 0
if bidirectional:
num_buckets //= 2
relative_buckets += (relative_position > 0) * num_buckets
relative_position = jnp.abs(relative_position)
else:
relative_position = -jnp.clip(relative_position, a_max=0)
# now relative_position is in the range [0, inf)
# half of the buckets are for exact increments in positions
max_exact = num_buckets // 2
is_small = relative_position < max_exact
# The other half of the buckets are for logarithmically bigger bins in positions up to max_distance
relative_position_if_large = max_exact + (
jnp.log(relative_position / max_exact) / jnp.log(max_distance / max_exact) * (num_buckets - max_exact)
)
relative_position_if_large = jnp.clip(relative_position_if_large, a_max=num_buckets - 1)
relative_buckets += jnp.where(is_small, relative_position, relative_position_if_large)
return relative_buckets.astype("i4")
def compute_bias(self, query_length, key_length):
"""Compute binned relative position bias"""
context_position = jnp.arange(query_length, dtype="i4")[:, None]
memory_position = jnp.arange(key_length, dtype="i4")[None, :]
relative_position = memory_position - context_position
relative_position_bucket = self._relative_position_bucket(
relative_position,
bidirectional=(not self.causal),
num_buckets=self.relative_attention_num_buckets,
max_distance=self.relative_attention_max_distance,
)
values = self.relative_attention_bias(relative_position_bucket)
values = values.transpose((2, 0, 1))[None, :, :, :]
return values
def _split_heads(self, hidden_states):
return hidden_states.reshape(hidden_states.shape[:2] + (self.n_heads, self.key_value_proj_dim))
def _merge_heads(self, hidden_states):
return hidden_states.reshape(hidden_states.shape[:2] + (self.inner_dim,))
@nn.compact
def _concatenate_to_cache(self, key, value, query, attention_mask):
"""
This function takes projected key, value states from a single input token and concatenates the states to cached
states from previous steps. This function is slighly adapted from the official Flax repository:
https://github.com/google/flax/blob/491ce18759622506588784b4fca0e4bf05f8c8cd/flax/linen/attention.py#L252
"""
# detect if we're initializing by absence of existing cache data.
is_initialized = self.has_variable("cache", "cached_key")
cached_key = self.variable("cache", "cached_key", jnp.zeros, key.shape, key.dtype)
cached_value = self.variable("cache", "cached_value", jnp.zeros, value.shape, value.dtype)
cache_index = self.variable("cache", "cache_index", lambda: jnp.array(0, dtype=jnp.int32))
if is_initialized:
*batch_dims, max_length, num_heads, depth_per_head = cached_key.value.shape
# update key, value caches with our new 1d spatial slices
cur_index = cache_index.value
indices = (0,) * len(batch_dims) + (cur_index, 0, 0)
key = jax.lax.dynamic_update_slice(cached_key.value, key, indices)
value = jax.lax.dynamic_update_slice(cached_value.value, value, indices)
cached_key.value = key
cached_value.value = value
num_updated_cache_vectors = query.shape[1]
cache_index.value = cache_index.value + num_updated_cache_vectors
# causal mask for cached decoder self-attention: our single query position should only attend to those key positions
# that have already been generated and cached, not the remaining zero elements.
pad_mask = jnp.broadcast_to(
jnp.arange(max_length) < cur_index + num_updated_cache_vectors,
tuple(batch_dims) + (1, num_updated_cache_vectors, max_length),
)
attention_mask = combine_masks(pad_mask, attention_mask)
return key, value, attention_mask
def _create_position_bias(
self, key_states, query_states, attention_mask, init_cache, seq_length, causal_attention_mask_shift
):
cache_is_filled = self.causal and self.has_variable("cache", "cached_key") and (not init_cache)
key_length = key_states.shape[1]
query_length = key_length if cache_is_filled else query_states.shape[1]
if self.has_relative_attention_bias:
position_bias = self.compute_bias(query_length, key_length)
elif attention_mask is not None:
position_bias = jnp.zeros_like(attention_mask)
else:
position_bias = jnp.zeros((1, self.n_heads, query_length, key_length), dtype=self.dtype)
# if key and values are already calculated, only the last query position bias should be taken
if cache_is_filled:
max_decoder_length = self.variables["cache"]["cached_key"].shape[1]
position_bias = jax.lax.dynamic_slice(
position_bias,
(0, 0, causal_attention_mask_shift, 0),
(1, self.n_heads, seq_length, max_decoder_length),
)
return position_bias
def __call__(
self,
hidden_states,
attention_mask=None,
key_value_states=None,
position_bias=None,
use_cache=False,
output_attentions=False,
deterministic=True,
init_cache=False,
):
"""
Self-attention (if key_value_states is None) or attention over source sentence (provided by key_value_states).
"""
batch_size, seq_length = hidden_states.shape[:2]
# q, k, v projections
query_states = self.q(hidden_states) # (batch_size, n_heads, seq_length, dim_per_head)
key_states = self.k(hidden_states) if key_value_states is None else self.k(key_value_states)
value_states = self.v(hidden_states) if key_value_states is None else self.v(key_value_states)
# reshape to (batch_size, seq_length, n_heads, head_dim)
query_states = self._split_heads(query_states)
key_states = self._split_heads(key_states)
value_states = self._split_heads(value_states)
# counter-act scaling in dot_product_attention_weights function
query_states *= jnp.sqrt(query_states.shape[-1])
# for fast decoding causal attention mask should be shifted
causal_attention_mask_shift = (
self.variables["cache"]["cache_index"] if (self.has_variable("cache", "cached_key") and self.causal) else 0
)
# create causal attention_mask; attention_mask has to be defined when model is causal
if self.causal:
causal_attention_mask = make_causal_mask(attention_mask, dtype="bool")
# fast decoding for generate requires special attention_mask
if self.has_variable("cache", "cached_key"):
max_decoder_length = self.variables["cache"]["cached_key"].shape[1]
causal_attention_mask = jax.lax.dynamic_slice(
causal_attention_mask,
(0, 0, causal_attention_mask_shift, 0),
(1, 1, seq_length, max_decoder_length),
)
# broadcast causal attention mask & attention mask to fit for merge
causal_attention_mask = jnp.broadcast_to(
causal_attention_mask, (batch_size,) + causal_attention_mask.shape[1:]
)
attention_mask = jnp.broadcast_to(
jnp.expand_dims(attention_mask, axis=(-3, -2)), causal_attention_mask.shape
)
attention_mask = combine_masks(attention_mask, causal_attention_mask)
elif attention_mask is not None:
attention_mask = jnp.expand_dims(attention_mask, axis=(-3, -2))
# During fast autoregressive decoding, we feed one position at a time,
# and cache the keys and values step by step.
if self.causal and (self.has_variable("cache", "cached_key") or init_cache):
key_states, value_states, attention_attention_mask = self._concatenate_to_cache(
key_states, value_states, query_states, attention_mask
)
# replace masked positions with -10_000
if attention_mask is not None:
mask_value = jnp.finfo(self.dtype).min
attention_mask = jax.lax.select(
attention_mask > 0,
jnp.full(attention_mask.shape, 0.0).astype(self.dtype),
jnp.full(attention_mask.shape, mask_value).astype(self.dtype),
)
if position_bias is None:
# compute position bias (only for first layer)
position_bias = self._create_position_bias(
key_states, query_states, attention_mask, init_cache, seq_length, causal_attention_mask_shift
)
if attention_mask is not None:
position_bias = position_bias + attention_mask
# create dropout rng
dropout_rng = None
if not deterministic and self.dropout > 0.0:
dropout_rng = self.make_rng("dropout")
# Softmax(QK^T)
attn_weights = dot_product_attention_weights(
query_states,
key_states,
bias=position_bias,
dropout_rng=dropout_rng,
dropout_rate=self.dropout,
broadcast_dropout=True,
deterministic=deterministic,
dtype=self.dtype,
)
# multiply with value states
attn_output = jnp.einsum("...hqk,...khd->...qhd", attn_weights, value_states)
# bring back to (batch_size, seq_length, d_model)
attn_output = self._merge_heads(attn_output)
# apply output matrix
attn_output = self.o(attn_output)
outputs = (attn_output, position_bias)
if output_attentions:
outputs = outputs + (attn_weights,)
return outputs
class FlaxLongT5LocalAttention(nn.Module):
config: LongT5Config
has_relative_attention_bias: bool = False
dtype: jnp.dtype = jnp.float32 # the dtype of the computation
def setup(self):
self.relative_attention_num_buckets = self.config.relative_attention_num_buckets
self.relative_attention_max_distance = self.config.relative_attention_max_distance
self.d_model = self.config.d_model
self.key_value_proj_dim = self.config.d_kv
self.n_heads = self.config.num_heads
self.local_radius = self.config.local_radius
self.block_len = self.local_radius + 1
self.dropout = self.config.dropout_rate
self.inner_dim = self.n_heads * self.key_value_proj_dim
q_init_std = self.config.initializer_factor * ((self.inner_dim * self.key_value_proj_dim) ** -0.5)
kv_init_std = self.config.initializer_factor * (self.inner_dim**-0.5)
o_init_std = self.config.initializer_factor * (self.inner_dim**-0.5)
self.q = nn.Dense(
self.inner_dim,
use_bias=False,
kernel_init=jax.nn.initializers.normal(q_init_std),
dtype=self.dtype,
)
self.k = nn.Dense(
self.inner_dim,
use_bias=False,
kernel_init=jax.nn.initializers.normal(kv_init_std),
dtype=self.dtype,
)
self.v = nn.Dense(
self.inner_dim,
use_bias=False,
kernel_init=jax.nn.initializers.normal(kv_init_std),
dtype=self.dtype,
)
self.o = nn.Dense(
self.d_model,
use_bias=False,
kernel_init=jax.nn.initializers.normal(o_init_std),
dtype=self.dtype,
)
if self.has_relative_attention_bias:
self.relative_attention_bias = nn.Embed(
self.relative_attention_num_buckets,
self.n_heads,
embedding_init=jax.nn.initializers.normal(kv_init_std),
)
@staticmethod
# Copied from transformers.models.t5.modeling_flax_t5.FlaxT5Attention._relative_position_bucket
def _relative_position_bucket(relative_position, bidirectional=True, num_buckets=32, max_distance=128):
"""
Adapted from Mesh Tensorflow:
https://github.com/tensorflow/mesh/blob/0cb87fe07da627bf0b7e60475d59f95ed6b5be3d/mesh_tensorflow/transformer/transformer_layers.py#L593
Translate relative position to a bucket number for relative attention. The relative position is defined as
memory_position - query_position, i.e. the distance in tokens from the attending position to the attended-to
position. If bidirectional=False, then positive relative positions are invalid. We use smaller buckets for
small absolute relative_position and larger buckets for larger absolute relative_positions. All relative
positions >=max_distance map to the same bucket. All relative positions <=-max_distance map to the same bucket.
This should allow for more graceful generalization to longer sequences than the model has been trained on
"""
relative_buckets = 0
if bidirectional:
num_buckets //= 2
relative_buckets += (relative_position > 0) * num_buckets
relative_position = jnp.abs(relative_position)
else:
relative_position = -jnp.clip(relative_position, a_max=0)
# now relative_position is in the range [0, inf)
# half of the buckets are for exact increments in positions
max_exact = num_buckets // 2
is_small = relative_position < max_exact
# The other half of the buckets are for logarithmically bigger bins in positions up to max_distance
relative_position_if_large = max_exact + (
jnp.log(relative_position / max_exact) / jnp.log(max_distance / max_exact) * (num_buckets - max_exact)
)
relative_position_if_large = jnp.clip(relative_position_if_large, a_max=num_buckets - 1)
relative_buckets += jnp.where(is_small, relative_position, relative_position_if_large)
return relative_buckets.astype("i4")
def compute_bias(self, block_length: int):
"""Compute binned relative position bias"""
memory_position = jnp.arange(3 * block_length, dtype="i4")
context_position = memory_position[block_length:-block_length]
relative_position = memory_position[None, :] - context_position[:, None]
relative_position_bucket = self._relative_position_bucket(
relative_position,
bidirectional=True,
num_buckets=self.relative_attention_num_buckets,
max_distance=self.relative_attention_max_distance,
)
values = self.relative_attention_bias(relative_position_bucket)
values = values.transpose((2, 0, 1))[None, None, :, :, :]
return values
def _split_heads(self, hidden_states):
return hidden_states.reshape(hidden_states.shape[:2] + (self.n_heads, self.key_value_proj_dim))
def _merge_heads(self, hidden_states):
return hidden_states.reshape(hidden_states.shape[0], -1, self.inner_dim)
def _create_position_bias(self, block_len: int, attention_mask: Optional[np.ndarray]) -> np.ndarray:
# position_bias shape: # (1, 1, n_heads, block_len, 3 * block_len)
if self.has_relative_attention_bias:
position_bias = self.compute_bias(block_len)
elif attention_mask is not None:
position_bias = jnp.zeros_like(attention_mask)
else:
position_bias = jnp.zeros((1, 1, self.n_heads, block_len, 3 * block_len), dtype=self.dtype)
return position_bias
def __call__(
self,
hidden_states,
attention_mask=None,
key_value_states=None,
position_bias=None,
output_attentions=False,
deterministic=True,
):
"""
Self-attention (if key_value_states is None) or attention over source sentence (provided by key_value_states).
"""
batch_size, seq_length = hidden_states.shape[:2]
# q, k, v projections
query_states = self.q(hidden_states) # (batch_size, n_heads, seq_length, dim_per_head)
key_states = self.k(hidden_states) if key_value_states is None else self.k(key_value_states)
value_states = self.v(hidden_states) if key_value_states is None else self.v(key_value_states)
# reshape to (batch_size, seq_length, n_heads, head_dim)
query_states = self._split_heads(query_states)
key_states = self._split_heads(key_states)
value_states = self._split_heads(value_states)
# Split into blocks -> (batch_size, num_blocks, block_len, n_heads, head_dim)
query_states = _split_into_blocks(query_states, self.block_len, axis=1)
key_states = _split_into_blocks(key_states, self.block_len, axis=1)
value_states = _split_into_blocks(value_states, self.block_len, axis=1)
# Concatenate 3 blocks for keys and values -> (batch_size, num_blocks, 3 * block_len, n_heads, dim_per_head)
key_states = _concatenate_3_blocks(key_states, block_axis=1, sequence_axis=2)
value_states = _concatenate_3_blocks(value_states, block_axis=1, sequence_axis=2)
# counter-act scaling in dot_product_attention_weights function
query_states *= jnp.sqrt(query_states.shape[-1])
if attention_mask is not None:
attention_mask = _get_local_attention_mask(attention_mask, self.block_len)
# replace masked positions with -10_000
attention_mask = jax.lax.select(
attention_mask > 0,
jnp.full(attention_mask.shape, 0.0).astype(self.dtype),
jnp.full(attention_mask.shape, -1e10).astype(self.dtype),
)
if position_bias is None:
# compute position bias (only for first layer)
position_bias = self._create_position_bias(self.block_len, attention_mask)
if attention_mask is not None:
position_bias = position_bias + attention_mask.swapaxes(1, 2)
# create dropout rng
dropout_rng = None
if not deterministic and self.dropout > 0.0:
dropout_rng = self.make_rng("dropout")
# Softmax(QK^T)
attn_weights = dot_product_attention_weights(
query_states,
key_states,
bias=position_bias,
dropout_rng=dropout_rng,
dropout_rate=self.dropout,
broadcast_dropout=True,
deterministic=deterministic,
dtype=self.dtype,
)
# multiply with value states
attn_output = jnp.einsum("...hqk,...khd->...qhd", attn_weights, value_states)
# bring back to (batch_size, seq_length, d_model)
attn_output = self._merge_heads(attn_output)
attn_output = attn_output[:, :seq_length, :]
# apply output matrix
attn_output = self.o(attn_output)
outputs = (attn_output, position_bias)
if output_attentions:
outputs = outputs + (attn_weights,)
return outputs
class FlaxLongT5TransientGlobalAttention(nn.Module):
config: LongT5Config
has_relative_attention_bias: bool = False
dtype: jnp.dtype = jnp.float32 # the dtype of the computation
def setup(self):
self.relative_attention_num_buckets = self.config.relative_attention_num_buckets
self.relative_attention_max_distance = self.config.relative_attention_max_distance
self.d_model = self.config.d_model
self.key_value_proj_dim = self.config.d_kv
self.n_heads = self.config.num_heads
self.local_radius = self.config.local_radius
self.block_len = self.local_radius + 1
self.global_block_size = self.config.global_block_size
self.dropout = self.config.dropout_rate
self.inner_dim = self.n_heads * self.key_value_proj_dim
q_init_std = self.config.initializer_factor * ((self.inner_dim * self.key_value_proj_dim) ** -0.5)
kv_init_std = self.config.initializer_factor * (self.inner_dim**-0.5)
o_init_std = self.config.initializer_factor * (self.inner_dim**-0.5)
self.q = nn.Dense(
self.inner_dim,
use_bias=False,
kernel_init=jax.nn.initializers.normal(q_init_std),
dtype=self.dtype,
)
self.k = nn.Dense(
self.inner_dim,
use_bias=False,
kernel_init=jax.nn.initializers.normal(kv_init_std),
dtype=self.dtype,
)
self.v = nn.Dense(
self.inner_dim,
use_bias=False,
kernel_init=jax.nn.initializers.normal(kv_init_std),
dtype=self.dtype,
)
self.o = nn.Dense(
self.d_model,
use_bias=False,
kernel_init=jax.nn.initializers.normal(o_init_std),
dtype=self.dtype,
)
if self.has_relative_attention_bias:
self.relative_attention_bias = nn.Embed(
self.relative_attention_num_buckets,
self.n_heads,
embedding_init=jax.nn.initializers.normal(kv_init_std),
)
# Relativen attention bias & Layer norm for global attention
if self.has_relative_attention_bias:
self.global_relative_attention_bias = nn.Embed(
self.relative_attention_num_buckets,
self.n_heads,
embedding_init=jax.nn.initializers.normal(kv_init_std),
)
self.global_input_layer_norm = FlaxLongT5LayerNorm(
self.config.d_model, eps=self.config.layer_norm_epsilon, dtype=self.dtype
)
@staticmethod
# Copied from transformers.models.t5.modeling_flax_t5.FlaxT5Attention._relative_position_bucket
def _relative_position_bucket(relative_position, bidirectional=True, num_buckets=32, max_distance=128):
"""
Adapted from Mesh Tensorflow:
https://github.com/tensorflow/mesh/blob/0cb87fe07da627bf0b7e60475d59f95ed6b5be3d/mesh_tensorflow/transformer/transformer_layers.py#L593
Translate relative position to a bucket number for relative attention. The relative position is defined as
memory_position - query_position, i.e. the distance in tokens from the attending position to the attended-to
position. If bidirectional=False, then positive relative positions are invalid. We use smaller buckets for
small absolute relative_position and larger buckets for larger absolute relative_positions. All relative
positions >=max_distance map to the same bucket. All relative positions <=-max_distance map to the same bucket.
This should allow for more graceful generalization to longer sequences than the model has been trained on
"""
relative_buckets = 0
if bidirectional:
num_buckets //= 2
relative_buckets += (relative_position > 0) * num_buckets
relative_position = jnp.abs(relative_position)
else:
relative_position = -jnp.clip(relative_position, a_max=0)
# now relative_position is in the range [0, inf)
# half of the buckets are for exact increments in positions
max_exact = num_buckets // 2
is_small = relative_position < max_exact
# The other half of the buckets are for logarithmically bigger bins in positions up to max_distance
relative_position_if_large = max_exact + (
jnp.log(relative_position / max_exact) / jnp.log(max_distance / max_exact) * (num_buckets - max_exact)
)
relative_position_if_large = jnp.clip(relative_position_if_large, a_max=num_buckets - 1)
relative_buckets += jnp.where(is_small, relative_position, relative_position_if_large)
return relative_buckets.astype("i4")
def compute_bias(self, block_length: int):
"""Compute binned relative position bias"""
memory_position = jnp.arange(3 * block_length, dtype="i4")
context_position = memory_position[block_length:-block_length]
relative_position = memory_position[None, :] - context_position[:, None]
relative_position_bucket = self._relative_position_bucket(
relative_position,
bidirectional=True,
num_buckets=self.relative_attention_num_buckets,
max_distance=self.relative_attention_max_distance,
)
values = self.relative_attention_bias(relative_position_bucket)
values = values.transpose((2, 0, 1))[None, None, :, :, :]
return values
def compute_side_bias(self, attention_mask: np.ndarray, global_segment_ids: np.ndarray) -> np.ndarray:
# (batch_size, 1, 1, seq_len, global_seq_len)
side_attention_mask = jnp.equal(attention_mask[..., None], global_segment_ids[:, None, :])[:, None, ...]
attention_side_bias = jax.lax.select(
side_attention_mask > 0,
jnp.full(side_attention_mask.shape, 0.0).astype(self.dtype),
jnp.full(side_attention_mask.shape, -1e10).astype(self.dtype),
)
# (batch_size, seq_len, global_seq_len)
side_relative_position = _make_side_relative_position_ids(attention_mask, self.global_block_size)
side_relative_position_bucket = self._relative_position_bucket(
side_relative_position,
bidirectional=True,
num_buckets=self.relative_attention_num_buckets,
max_distance=self.relative_attention_max_distance,
)
# (batch_size, seq_len, global_seq_len, num_heads)
side_bias = self.global_relative_attention_bias(side_relative_position_bucket)
# (batch_size, 1, num_heads, seq_len, global_seq_len)
side_bias = jnp.transpose(side_bias, (0, 3, 1, 2))
# (batch_size, num_heads, seq_len, global_seq_len)
attention_side_bias = attention_side_bias + side_bias
return attention_side_bias
def _split_heads(self, hidden_states):
return hidden_states.reshape(hidden_states.shape[:2] + (self.n_heads, self.key_value_proj_dim))
def _merge_heads(self, hidden_states):
return hidden_states.reshape(hidden_states.shape[0], -1, self.inner_dim)
def _create_position_bias(self, block_len: int, attention_mask: Optional[np.ndarray]) -> np.ndarray:
# position_bias shape: # (1, 1, n_heads, block_len, 3 * block_len)
if self.has_relative_attention_bias:
position_bias = self.compute_bias(block_len)
elif attention_mask is not None:
position_bias = jnp.zeros_like(attention_mask)
else:
position_bias = jnp.zeros((1, 1, self.n_heads, block_len, 3 * block_len), dtype=self.dtype)
return position_bias
def __call__(
self,
hidden_states,
attention_mask=None,
key_value_states=None,
position_bias=None,
output_attentions=False,
deterministic=True,
):
"""
Self-attention (if key_value_states is None) or attention over source sentence (provided by key_value_states).
"""
batch_size, seq_length = hidden_states.shape[:2]
# Prepare components for transient-global attention
# Obtain block_ids and global_segment_ids
# global_seq_len := seq_len // self.global_block_size
# shapes: (batch_size, seq_len) & (batch_size, global_seq_len)
block_ids, global_segment_ids = _make_global_fixed_block_ids(
attention_mask if attention_mask is not None else jnp.ones((batch_size, seq_length)),
self.global_block_size,
)
# Create global inputs
_global_seq_len = global_segment_ids.shape[-1]
global_inputs = _create_global_aggregates(hidden_states, block_ids, _global_seq_len)
global_inputs = self.global_input_layer_norm(global_inputs)