modeling_mobilellm_p1.py

import math
from dataclasses import dataclass
from typing import Callable, Optional, Union
import copy

import torch
import torch.nn as nn
import torch.nn.functional as F

from transformers.activations import ACT2FN
from transformers.cache_utils import Cache, DynamicCache
from transformers.generation import GenerationMixin
from transformers.integrations import use_kernel_forward_from_hub
from transformers.masking_utils import (
    create_causal_mask,
    create_sliding_window_causal_mask,
)
from transformers.modeling_flash_attention_utils import FlashAttentionKwargs
from transformers.modeling_layers import GradientCheckpointingLayer
from transformers.modeling_outputs import (
    BaseModelOutput,
    BaseModelOutputWithPast,
    CausalLMOutputWithPast,
    ModelOutput,
)
from transformers.modeling_rope_utils import dynamic_rope_update, ROPE_INIT_FUNCTIONS
from transformers.modeling_utils import ALL_ATTENTION_FUNCTIONS, PreTrainedModel

from transformers.models.llama4.configuration_llama4 import (
    Llama4Config,
    Llama4TextConfig,
    Llama4VisionConfig,
)
from transformers.models.llama4.modeling_llama4 import (
    apply_rotary_emb,
    eager_attention_forward,
    Llama4PreTrainedModel,
    Llama4TextDecoderLayer,
    Llama4TextL2Norm,
    Llama4TextMLP,
    Llama4TextMoe,
    Llama4TextRMSNorm,
    Llama4TextRotaryEmbedding,
    Llama4TextAttention,
    Llama4TextDecoderLayer,
    Llama4ForCausalLM
)
from transformers.processing_utils import Unpack
from transformers.utils import (
    auto_docstring,
    can_return_tuple,
    logging,
    TransformersKwargs,
)
from transformers.utils.deprecation import deprecate_kwarg
from transformers.utils.generic import check_model_inputs

from .configuration_mobilellm_p1 import MobileLLMP1TextConfig

logger = logging.get_logger(__name__)

class MobileLLMP1TextAttention(nn.Module):
    """Multi-headed attention from 'Attention Is All You Need' paper"""

    def __init__(self, config: MobileLLMP1TextConfig, layer_idx):
        super().__init__()
        self.config = config
        self.layer_idx = layer_idx
        self.is_sliding = config.layer_types[layer_idx] == "sliding_attention"
        self.head_dim = getattr(
            config, "head_dim", config.hidden_size // config.num_attention_heads
        )
        self.num_attention_heads = config.num_attention_heads
        self.num_key_value_groups = (
            config.num_attention_heads // config.num_key_value_heads
        )
        self.num_key_value_heads = config.num_key_value_heads
        self.scaling = self.head_dim**-0.5
        self.attn_scale = config.attn_scale
        self.floor_scale = config.floor_scale
        self.attn_temperature_tuning = config.attn_temperature_tuning
        self.attention_dropout = config.attention_dropout
        self.is_causal = True
        self.use_rope = config.no_rope_layers[layer_idx]
        self.sliding_window = config.sliding_window if self.is_sliding else None
        self.q_proj = nn.Linear(
            config.hidden_size,
            config.num_attention_heads * self.head_dim,
            bias=config.attention_bias,
        )
        self.k_proj = nn.Linear(
            config.hidden_size,
            config.num_key_value_heads * self.head_dim,
            bias=config.attention_bias,
        )
        self.v_proj = nn.Linear(
            config.hidden_size,
            config.num_key_value_heads * self.head_dim,
            bias=config.attention_bias,
        )
        self.o_proj = nn.Linear(
            config.num_attention_heads * self.head_dim,
            config.hidden_size,
            bias=config.attention_bias,
        )
        if self.config.use_qk_norm and self.use_rope:
            self.qk_norm = Llama4TextL2Norm(config.rms_norm_eps)

    def forward(
        self,
        hidden_states: torch.Tensor,
        position_embeddings: tuple[torch.Tensor, torch.Tensor],
        attention_mask: Optional[torch.Tensor],
        past_key_values: Optional[Cache] = None,
        cache_position: Optional[torch.LongTensor] = None,
        **kwargs: Unpack[FlashAttentionKwargs],
    ) -> tuple[torch.Tensor, Optional[torch.Tensor], Optional[tuple[torch.Tensor]]]:
        input_shape = hidden_states.shape[:-1]
        hidden_shape = (*input_shape, -1, self.head_dim)

        query_states = self.q_proj(hidden_states).view(hidden_shape)
        key_states = self.k_proj(hidden_states).view(*input_shape, -1, self.head_dim)
        value_states = self.v_proj(hidden_states).view(hidden_shape).transpose(1, 2)

        if self.use_rope:  # the 16E model skips rope for long context on certain layers
            query_states, key_states = apply_rotary_emb(
                query_states, key_states, position_embeddings.to(query_states.device)
            )

        if hasattr(self, "qk_norm"):  # the 128E model does not use qk_norm
            query_states = self.qk_norm(query_states)
            key_states = self.qk_norm(key_states)

        # Use temperature tuning from https://huggingface.co/papers/2501.19399) to NoROPE layers
        if self.attn_temperature_tuning and not self.use_rope:
            attn_scales = (
                torch.log(
                    torch.floor((cache_position.float() + 1.0) / self.floor_scale) + 1.0
                )
                * self.attn_scale
                + 1.0
            )
            attn_scales = attn_scales.view((1, input_shape[-1], 1, 1)).expand(
                (*input_shape, 1, 1)
            )  # batch size > 1
            query_states = (query_states * attn_scales).to(query_states.dtype)

        query_states = query_states.transpose(1, 2)
        key_states = key_states.transpose(1, 2)

        if past_key_values is not None:
            # sin and cos are specific to RoPE models; cache_position needed for the static cache
            cache_kwargs = {"cache_position": cache_position}
            key_states, value_states = past_key_values.update(
                key_states, value_states, self.layer_idx, cache_kwargs
            )

        attention_interface: Callable = eager_attention_forward
        if self.config._attn_implementation != "eager":
            attention_interface = ALL_ATTENTION_FUNCTIONS[
                self.config._attn_implementation
            ]

        attn_output, attn_weights = attention_interface(
            self,
            query_states,
            key_states,
            value_states,
            attention_mask,
            dropout=0.0 if not self.training else self.attention_dropout,
            scaling=self.scaling,
            sliding_window=self.sliding_window,
            **kwargs,
        )

        attn_output = attn_output.reshape(*input_shape, -1).contiguous()
        attn_output = self.o_proj(attn_output)
        return attn_output, attn_weights


class MobileLLMP1TextDecoderLayer(GradientCheckpointingLayer):
    def __init__(self, config, layer_idx):
        super().__init__()
        self.hidden_size = config.hidden_size
        self.layer_idx = layer_idx
        self.attention_type = config.layer_types[layer_idx]
        self.self_attn = MobileLLMP1TextAttention(config, layer_idx)
        self.is_moe_layer = layer_idx in config.moe_layers
        if self.is_moe_layer:  # the 128E model interleaves dense / sparse
            self.feed_forward = Llama4TextMoe(config)
        else:
            self.feed_forward = Llama4TextMLP(
                config, intermediate_size=config.intermediate_size_mlp
            )

        self.input_layernorm = Llama4TextRMSNorm(
            config.hidden_size, eps=config.rms_norm_eps
        )
        self.post_attention_layernorm = Llama4TextRMSNorm(
            config.hidden_size, eps=config.rms_norm_eps
        )

    def forward(
        self,
        hidden_states: torch.Tensor,
        attention_mask: Optional[torch.Tensor] = None,
        position_ids: Optional[torch.LongTensor] = None,
        past_key_values: Optional[Cache] = None,
        use_cache: Optional[bool] = False,
        cache_position: Optional[torch.LongTensor] = None,
        position_embeddings: Optional[tuple[torch.Tensor, torch.Tensor]] = None,  # necessary, but kept here for BC
        **kwargs: Unpack[FlashAttentionKwargs],
    ) -> tuple[
        torch.FloatTensor, Optional[tuple[torch.FloatTensor, torch.FloatTensor]]
    ]:
        residual = hidden_states
        hidden_states = self.input_layernorm(hidden_states)

        # Self Attention
        attention_states, _ = self.self_attn(
            hidden_states=hidden_states,
            position_embeddings=position_embeddings,
            attention_mask=attention_mask,
            past_key_values=past_key_values,
            use_cache=use_cache,
            cache_position=cache_position,
            **kwargs,
        )
        hidden_states = residual + attention_states

        # Fully Connected
        residual = hidden_states
        hidden_states = self.post_attention_layernorm(hidden_states)
        hidden_states = self.feed_forward(hidden_states)
        if self.is_moe_layer:
            hidden_states, _ = hidden_states
        hidden_states = residual + hidden_states.view(residual.shape)
        return hidden_states

class MobileLLMP1TextModel(Llama4PreTrainedModel):
    _no_split_modules = ["MobileLLMP1TextDecoderLayer"]
    base_model_prefix = "model"
    config: MobileLLMP1TextConfig
    _can_record_outputs = {
        "attentions": MobileLLMP1TextAttention,
        "hidden_states": MobileLLMP1TextDecoderLayer,
        "router_logits": Llama4TextMoe,
    }

    def __init__(self, config: MobileLLMP1TextConfig):
        super().__init__(config)
        self.padding_idx = config.pad_token_id
        self.vocab_size = config.vocab_size

        self.embed_tokens = nn.Embedding(
            config.vocab_size, config.hidden_size, self.padding_idx
        )
        self.layers = nn.ModuleList(
            [
                MobileLLMP1TextDecoderLayer(config, layer_idx)
                for layer_idx in range(config.num_hidden_layers)
            ]
        )
        self.norm = Llama4TextRMSNorm(config.hidden_size, eps=config.rms_norm_eps)
        self.rotary_emb = Llama4TextRotaryEmbedding(config=config)
        self.gradient_checkpointing = False

        # Initialize weights and apply final processing
        self.post_init()

    def forward(
        self,
        input_ids: Optional[torch.LongTensor] = None,
        attention_mask: Optional[torch.Tensor] = None,
        position_ids: Optional[torch.LongTensor] = None,
        past_key_values: Optional[Cache] = None,
        inputs_embeds: Optional[torch.FloatTensor] = None,
        use_cache: Optional[bool] = None,
        cache_position: Optional[torch.LongTensor] = None,
        **kwargs: Unpack[TransformersKwargs],
    ) -> Union[tuple, BaseModelOutputWithPast]:
        if (input_ids is None) ^ (inputs_embeds is not None):
            raise ValueError(
                "You must specify exactly one of input_ids or inputs_embeds"
            )

        if inputs_embeds is None:
            inputs_embeds = self.embed_tokens(
                input_ids.to(self.embed_tokens.weight.device)
            )

        if use_cache and past_key_values is None:
            past_key_values = DynamicCache(config=self.config)

        if cache_position is None:
            past_seen_tokens = (
                past_key_values.get_seq_length() if past_key_values is not None else 0
            )
            cache_position = torch.arange(
                past_seen_tokens,
                past_seen_tokens + inputs_embeds.shape[1],
                device=inputs_embeds.device,
            )

        if position_ids is None:
            position_ids = cache_position.unsqueeze(0)

        # It may already have been prepared by e.g. `generate`
        if not isinstance(causal_mask_mapping := attention_mask, dict):
            # Prepare mask arguments
            mask_kwargs = {
                "config": self.config,
                "input_embeds": inputs_embeds,
                "attention_mask": attention_mask,
                "cache_position": cache_position,
                "past_key_values": past_key_values,
                "position_ids": position_ids,
            }
            sliding_mask_kwargs = mask_kwargs.copy()
            del sliding_mask_kwargs['position_ids']

            # Create the masks
            causal_mask_mapping = {
                "full_attention": create_causal_mask(**mask_kwargs),
                "sliding_attention": create_sliding_window_causal_mask(
                    **sliding_mask_kwargs
                ),
            }

        hidden_states = inputs_embeds

        # create position embeddings to be shared across the decoder layers
        freq_cis = self.rotary_emb(hidden_states, position_ids)

        # found = False
        for decoder_layer in self.layers[: self.config.num_hidden_layers]:
            hidden_states = decoder_layer(
                hidden_states,
                attention_mask=causal_mask_mapping[decoder_layer.attention_type],
                position_ids=position_ids,
                past_key_values=past_key_values,
                use_cache=use_cache,
                cache_position=cache_position,
                position_embeddings=freq_cis,
                **kwargs,
            )
        hidden_states = self.norm(hidden_states)

        return BaseModelOutputWithPast(
            last_hidden_state=hidden_states,
            past_key_values=past_key_values if use_cache else None,
        )


class MobileLLMP1ForCausalLM(Llama4PreTrainedModel, GenerationMixin):
    _no_split_modules = ["MobileLLMP1TextDecoderLayer"]
    base_model_prefix = "language_model"
    _tied_weights_keys = ["lm_head.weight"]
    _tp_plan = {"lm_head": "colwise_rep"}
    config: MobileLLMP1TextConfig

    def __init__(self, config: MobileLLMP1TextConfig):
        super().__init__(config)
        self.model = MobileLLMP1TextModel(config)
        self.vocab_size = config.vocab_size
        self.lm_head = nn.Linear(config.hidden_size, config.vocab_size, bias=False)

        # Initialize weights and apply final processing
        self.post_init()

    def forward(
        self,
        input_ids: Optional[torch.LongTensor] = None,
        attention_mask: Optional[torch.Tensor] = None,
        position_ids: Optional[torch.LongTensor] = None,
        past_key_values: Optional[Union[Cache, list[torch.FloatTensor]]] = None,
        inputs_embeds: Optional[torch.FloatTensor] = None,
        labels: Optional[torch.LongTensor] = None,
        use_cache: Optional[bool] = None,
        cache_position: Optional[torch.LongTensor] = None,
        logits_to_keep: Union[int, torch.Tensor] = 0,
        **kwargs: Unpack[TransformersKwargs],
    ) -> Union[tuple, CausalLMOutputWithPast]:
        r"""
        labels (`torch.LongTensor` of shape `(batch_size, sequence_length)`, *optional*):
            Labels for computing the masked language modeling loss. Indices should either be in `[0, ...,
            config.vocab_size]` or -100 (see `input_ids` docstring). Tokens with indices set to `-100` are ignored
            (masked), the loss is only computed for the tokens with labels in `[0, ..., config.vocab_size]`.

        Example:

        ```python
        >>> from transformers import AutoTokenizer, Llama4ForCausalLM

        >>> model = Llama4ForCausalLM.from_pretrained("meta-llama4/Llama4-2-7b-hf")
        >>> tokenizer = AutoTokenizer.from_pretrained("meta-llama4/Llama4-2-7b-hf")

        >>> prompt = "Hey, are you conscious? Can you talk to me?"
        >>> inputs = tokenizer(prompt, return_tensors="pt")

        >>> # Generate
        >>> generate_ids = model.generate(inputs.input_ids, max_length=30)
        >>> tokenizer.batch_decode(generate_ids, skip_special_tokens=True, clean_up_tokenization_spaces=False)[0]
        "Hey, are you conscious? Can you talk to me?\nI'm not conscious, but I can talk to you."
        ```"""
        outputs = self.model(
            input_ids=input_ids,
            attention_mask=attention_mask,
            position_ids=position_ids,
            past_key_values=past_key_values,
            inputs_embeds=inputs_embeds,
            use_cache=use_cache,
            cache_position=cache_position,
            **kwargs,
        )

        hidden_states = outputs[0]
        # Only compute necessary logixts, and do not upcast them to float if we are not computing the loss
        slice_indices = (
            slice(-logits_to_keep, None)
            if isinstance(logits_to_keep, int)
            else logits_to_keep
        )
        logits = self.lm_head(hidden_states[:, slice_indices, :])
        loss = None
        if labels is not None:
            loss = self.loss_function(
                logits=logits,
                labels=labels,
                vocab_size=self.config.vocab_size,
                **kwargs,
            )

        return CausalLMOutputWithPast(
            loss=loss,
            logits=logits,
            past_key_values=outputs.past_key_values,
            hidden_states=outputs.hidden_states,
            attentions=outputs.attentions,
        )

__all__ = [
    "MobileLLMP1ForCausalLM",
    "MobileLLMP1TextModel",
    "MobileLLMP1TextDecoderLayer",
    "MobileLLMP1TextAttention",
]