EasyLM/jax_utils.py

import os
import math
from typing import Any, Mapping, Text, Tuple, Union, NamedTuple
from functools import partial
import re
import dataclasses
import random
from ml_collections import ConfigDict
from ml_collections.config_dict.config_dict import placeholder

import flax
import jax
import jax.numpy as jnp
from jax.sharding import PartitionSpec as PS
from jax.sharding import Mesh
from jax.experimental import mesh_utils
from jax.experimental.pjit import with_sharding_constraint as _with_sharding_constraint
from jax.experimental.pjit import pjit
from jax.interpreters import pxla
import numpy as np
from transformers import FlaxLogitsWarper


class JaxRNG(object):
    """ A convenient stateful Jax RNG wrapper. Can be used to wrap RNG inside
        pure function.
    """

    @classmethod
    def from_seed(cls, seed):
        return cls(jax.random.PRNGKey(seed))

    def __init__(self, rng):
        self.rng = rng

    def __call__(self, keys=None):
        if keys is None:
            self.rng, split_rng = jax.random.split(self.rng)
            return split_rng
        elif isinstance(keys, int):
            split_rngs = jax.random.split(self.rng, num=keys + 1)
            self.rng = split_rngs[0]
            return tuple(split_rngs[1:])
        else:
            split_rngs = jax.random.split(self.rng, num=len(keys) + 1)
            self.rng = split_rngs[0]
            return {key: val for key, val in zip(keys, split_rngs[1:])}


class JaxDistributedConfig(object):
    """ Utility class for initializing JAX distributed. """

    @staticmethod
    def get_default_config(updates=None):
        config = ConfigDict()
        config.initialize_jax_distributed = False
        config.coordinator_address = placeholder(str)
        config.num_processes = placeholder(int)
        config.process_id = placeholder(int)
        config.local_device_ids = placeholder(str)

        if updates is not None:
            config.update(ConfigDict(updates).copy_and_resolve_references())
        return config

    @classmethod
    def initialize(cls, config):
        config = cls.get_default_config(config)
        if config.initialize_jax_distributed:
            if config.local_device_ids is not None:
                local_device_ids = [int(x) for x in config.local_device_ids.split(',')]
            else:
                local_device_ids = None

            jax.distributed.initialize(
                coordinator_address=config.coordinator_address,
                num_processes=config.num_processes,
                process_id=config.process_id,
                local_device_ids=local_device_ids,
            )


class FlaxTemperatureLogitsWarper(FlaxLogitsWarper):
    """ JIT traceable version of FlaxLogitsWarper that performs temperature scaling."""
    def __init__(self, temperature):
        self.temperature = temperature

    def __call__(self, input_ids, scores, cur_len):
        return scores / jnp.clip(self.temperature, a_min=1e-8)


def make_shard_and_gather_fns(partition_specs, dtype_specs=None):
    """ Create pytree of sharding and gathering functions from pytree of
        partition specs.
    """
    float_dtypes = (jnp.bfloat16, jnp.float16, jnp.float32, jnp.float64)

    def make_to_dtype_fn(dtype_spec):
        def to_dtype(tensor):
            if dtype_specs in float_dtypes and getattr(tensor, 'dtype', None) in float_dtypes:
                # Convert all float tensors to the same dtype
                return tensor.astype(dtype_specs)
            elif hasattr(dtype_spec, 'dtype') and hasattr(tensor, 'dtype'):
                return tensor.astype(dtype_spec.dtype)
            return tensor
        return to_dtype

    def make_shard_fn(partition_spec, dtype_spec=None):
        jax_shard_function = pjit(
            make_to_dtype_fn(dtype_spec),
            in_shardings=None,
            out_shardings=partition_spec
        )
        def shard_fn(tensor):
            return jax_shard_function(tensor).block_until_ready()
        return shard_fn

    def make_gather_fn(partition_spec, dtype_spec=None):
        jax_gather_fn = pjit(
            make_to_dtype_fn(dtype_spec),
            in_shardings=partition_spec,
            out_shardings=None
        )
        def gather_fn(tensor):
            return jax.device_get(jax_gather_fn(tensor))
        return gather_fn

    if dtype_specs is None or dtype_specs in float_dtypes:
        shard_fns = jax.tree_util.tree_map(make_shard_fn, partition_specs)
        gather_fns = jax.tree_util.tree_map(make_gather_fn, partition_specs)
    else:
        shard_fns = jax.tree_util.tree_map(
            make_shard_fn, partition_specs, dtype_specs
        )
        gather_fns = jax.tree_util.tree_map(
            make_gather_fn, partition_specs, dtype_specs
        )
    return shard_fns, gather_fns


def set_random_seed(seed):
    np.random.seed(seed)
    random.seed(seed)
    init_rng(seed)


def get_jax_mesh(axis_dims, names):
    if axis_dims.startswith('!'):
        # Allow splitting a physical mesh axis if needed
        mesh_axis_splitting = True
        axis_dims = axis_dims[1:]
    else:
        mesh_axis_splitting = False

    if ':' in axis_dims:
        dims = []
        dim_names = []
        for axis in axis_dims.split(','):
            name, dim = axis.split(':')
            assert name in names
            dims.append(int(dim))
            dim_names.append(name)
        assert(set(dim_names) == set(names))
    else:
        dims = [int(x) for x in axis_dims.split(',')]
        dim_names = names
    assert len(dims) == len(names)
    mesh_shape = np.arange(jax.device_count()).reshape(dims).shape
    if mesh_axis_splitting:
        physical_mesh = np.array(jax.devices()).reshape(mesh_shape)
    else:
        physical_mesh = mesh_utils.create_device_mesh(mesh_shape)
    return Mesh(physical_mesh, dim_names)


def names_in_current_mesh(*names):
    """ Check if current mesh axes contain these names. """
    mesh_axis_names = pxla.thread_resources.env.physical_mesh.axis_names
    return set(names) <= set(mesh_axis_names)


def get_names_from_parition_spec(partition_specs):
    """ Return axis names from partition specs. """
    names = set()
    if isinstance(partition_specs, dict):
        partition_specs = partition_specs.values()
    for item in partition_specs:
        if item is None:
            continue
        elif isinstance(item, str):
            names.add(item)
        else:
            names.update(get_names_from_parition_spec(item))

    return list(names)


def with_sharding_constraint(x, partition_specs):
    """ A smarter version of with_sharding_constraint that only applies the
        constraint if the current mesh contains the axes in the partition specs.
    """
    axis_names = get_names_from_parition_spec(partition_specs)
    if names_in_current_mesh(*axis_names):
        x = _with_sharding_constraint(x, partition_specs)
    return x


def wrap_function_with_rng(rng):
    """ To be used as decorator, automatically bookkeep a RNG for the wrapped function. """
    def wrap_function(function):
        def wrapped(*args, **kwargs):
            nonlocal rng
            rng, split_rng = jax.random.split(rng)
            return function(split_rng, *args, **kwargs)
        return wrapped
    return wrap_function


def init_rng(seed):
    global jax_utils_rng
    jax_utils_rng = JaxRNG.from_seed(seed)


def next_rng(*args, **kwargs):
    global jax_utils_rng
    return jax_utils_rng(*args, **kwargs)


def get_metrics(metrics, unreplicate=False, stack=False):
    if unreplicate:
        metrics = flax.jax_utils.unreplicate(metrics)
    metrics = jax.device_get(metrics)
    if stack:
        return jax.tree_map(lambda *args: np.stack(args), *metrics)
    else:
        return {key: float(val) for key, val in metrics.items()}


def mse_loss(val, target, valid=None):
    if valid is None:
        valid = jnp.ones((*target.shape[:2], 1))
    valid = valid.astype(jnp.float32)
    loss = jnp.mean(
        jnp.where(
            valid > 0.0,
            jnp.square(val - target),
            0.0
        )
    )
    return loss


def cross_entropy_loss_and_accuracy(logits, tokens, valid=None):
    if valid is None:
        valid = jnp.ones(tokens.shape[:2])
    valid = valid.astype(jnp.float32)
    valid_text_length = jnp.maximum(jnp.sum(valid, axis=-1), 1e-10)
    logits = logits.astype(jnp.float32) # for numerical stability
    token_log_prob = jnp.squeeze(
        jnp.take_along_axis(
            jax.nn.log_softmax(logits, axis=-1),
            jnp.expand_dims(tokens, -1),
            axis=-1,
        ),
        -1,
    )
    token_log_prob = jnp.where(valid > 0.0, token_log_prob, jnp.array(0.0))
    loss = -jnp.mean(jnp.sum(token_log_prob, axis=-1) / valid_text_length)
    correct = jnp.where(
        valid > 0.0,
        jnp.argmax(logits, axis=-1) == tokens,
        jnp.array(False)
    )
    accuracy = jnp.mean(jnp.sum(correct, axis=-1) / valid_text_length)
    return loss, accuracy


def global_norm(tree):
    """ Return the global L2 norm of a pytree. """
    squared = jax.tree_util.tree_map(lambda x: jnp.sum(jnp.square(x)), tree)
    flattened, _ = jax.flatten_util.ravel_pytree(squared)
    return jnp.sqrt(jnp.sum(flattened))


def average_metrics(metrics):
    return jax.tree_map(
        lambda *args: jnp.mean(jnp.stack(args)),
        *metrics
    )


def get_float_dtype_by_name(dtype):
    return {
        'bf16': jnp.bfloat16,
        'bfloat16': jnp.bfloat16,
        'fp16': jnp.float16,
        'float16': jnp.float16,
        'fp32': jnp.float32,
        'float32': jnp.float32,
        'fp64': jnp.float64,
        'float64': jnp.float64,
    }[dtype]


def float_tensor_to_dtype(tensor, dtype):
    if dtype is None or dtype == '':
        return tensor
    if isinstance(dtype, str):
        dtype = get_float_dtype_by_name(dtype)
    float_dtypes = (jnp.bfloat16, jnp.float16, jnp.float32, jnp.float64)
    if getattr(tensor, 'dtype', None) in float_dtypes:
        tensor = tensor.astype(dtype)
    return tensor


def float_to_dtype(tree, dtype):
    return jax.tree_util.tree_map(
        partial(float_tensor_to_dtype, dtype=dtype), tree
    )


def get_gradient_checkpoint_policy(name):
    return {
        'everything_saveable': jax.checkpoint_policies.everything_saveable,
        'nothing_saveable': jax.checkpoint_policies.nothing_saveable,
        'checkpoint_dots': jax.checkpoint_policies.checkpoint_dots,
        'checkpoint_dots_with_no_batch_dims': jax.checkpoint_policies.checkpoint_dots_with_no_batch_dims,
    }[name]


def tree_path_to_string(path, sep=None):
    keys = []
    for key in path:
        if isinstance(key, jax.tree_util.SequenceKey):
            keys.append(str(key.idx))
        elif isinstance(key, jax.tree_util.DictKey):
            keys.append(str(key.key))
        elif isinstance(key, jax.tree_util.GetAttrKey):
            keys.append(str(key.name))
        elif isinstance(key, jax.tree_util.FlattenedIndexKey):
            keys.append(str(key.key))
        else:
            keys.append(str(key))
    if sep is None:
        return tuple(keys)
    return sep.join(keys)


def flatten_tree(xs, is_leaf=None, sep=None):
    flattened, _ = jax.tree_util.tree_flatten_with_path(xs, is_leaf=is_leaf)
    output = {}
    for key, val in flattened:
        output[tree_path_to_string(key, sep=sep)] = val
    return output


def named_tree_map(f, tree, *rest, is_leaf=None, sep=None):
    """ An extended version of jax.tree_util.tree_map, where the mapped function
        f takes both the name (path) and the tree leaf as input.
    """
    return jax.tree_util.tree_map_with_path(
        lambda path, x, *r: f(tree_path_to_string(path, sep=sep), x, *r),
        tree, *rest,
        is_leaf=is_leaf
    )


def match_partition_rules(rules, params):
    """ Returns a pytree of PartitionSpec according to rules. Supports handling
        Flax TrainState and Optax optimizer state.
    """
    def get_partition_spec(name, leaf):
        if len(leaf.shape) == 0 or np.prod(leaf.shape) == 1:
            """ Don't partition scalar values. """
            return PS()
        for rule, ps in rules:
            if re.search(rule, name) is not None:
                return ps
        raise ValueError(f'Partition rule not found for param: {name}')
    return named_tree_map(get_partition_spec, params, sep='/')


def get_weight_decay_mask(exclusions):
    """ Return a weight decay mask function that computes the pytree masks
        according to the given exclusion rules.
    """
    def decay(name, _):
        for rule in exclusions:
            if re.search(rule, name) is not None:
                return False
        return True

    def weight_decay_mask(params):
        return named_tree_map(decay, params, sep='/')

    return weight_decay_mask


def tree_apply(fns, tree):
    """ Apply a pytree of functions to the pytree. """
    return jax.tree_util.tree_map(lambda fn, x: fn(x), fns, tree)