modeling.py

"""
SabiYarn Model Implementation - Optimized Version
Memory-efficient with performance optimizations for generation.
Matches original implementation exactly but with memory optimizations.
"""

from transformers import PreTrainedModel, AutoConfig, AutoModel, AutoModelForCausalLM
from transformers.modeling_outputs import CausalLMOutputWithPast
# use package-relative import to avoid colliding with unrelated `model` packages
from .configuration import GPTJXConfig
from typing import Optional
from torch import nn
import torch
import torch.nn.functional as F
import math


from transformers import AutoConfig, PreTrainedModel, AutoModelForCausalLM
from typing import List, Optional
from torch import nn
# from model import LayerNorm, BlockJ
from transformers.modeling_outputs import CausalLMOutputWithPast
import torch
import math
from torch.nn import functional as F
from transformers import AutoConfig, AutoModel


   
   
class LayerNorm(nn.Module):
    """ LayerNorm but with an optional bias. PyTorch doesn't support simply bias=False """

    def __init__(self, ndim, bias):
        super().__init__()
        self.weight = nn.Parameter(torch.ones(ndim))
        self.bias = nn.Parameter(torch.zeros(ndim)) if bias else None

    def forward(self, input):
        return F.layer_norm(input, self.weight.shape, self.weight, self.bias, 1e-5)

class CausalSelfAttention(nn.Module):

    def __init__(self, config):
        super().__init__()
        assert config.n_embd % config.n_heads == 0
        # key, query, value projections for all heads, but in a batch
        self.c_attn = nn.Linear(config.n_embd, 3 * config.n_embd, bias=config.bias)
        # output projection
        self.c_proj = nn.Linear(config.n_embd, config.n_embd, bias=config.bias)
        # regularization
        self.attn_dropout = nn.Dropout(config.dropout)
        self.resid_dropout = nn.Dropout(config.dropout)
        self.n_heads = config.n_heads
        self.n_embd = config.n_embd
        self.dropout = config.dropout
        # flash attention make GPU go brrrrr but support is only in PyTorch >= 2.0
        self.flash = hasattr(torch.nn.functional, 'scaled_dot_product_attention')
        # if not self.flash:
        #     print("WARNING: using slow attention. Flash Attention requires PyTorch >= 2.0")
            # causal mask to ensure that attention is only applied to the left in the input sequence

    def forward(self, x, attn_mask=None):
        B, T, C = x.size() # batch size, sequence length, embedding dimensionality (n_embd)

        # calculate query, key, values for all heads in batch and move head forward to be the batch dim
        q, k, v  = self.c_attn(x).split(self.n_embd, dim=2)
        k = k.view(B, T, self.n_heads, C // self.n_heads).transpose(1, 2) # (B, nh, T, hs)
        q = q.view(B, T, self.n_heads, C // self.n_heads).transpose(1, 2) # (B, nh, T, hs)
        v = v.view(B, T, self.n_heads, C // self.n_heads).transpose(1, 2) # (B, nh, T, hs)

        # causal self-attention; Self-attend: (B, nh, T, hs) x (B, nh, hs, T) -> (B, nh, T, T)
        if self.flash:
            if attn_mask is not None:
            # efficient attention using Flash Attention CUDA kernels
                attn_mask = attn_mask.to(torch.bool)
                y = torch.nn.functional.scaled_dot_product_attention(q, k, v, attn_mask=attn_mask, dropout_p=self.dropout if self.training else 0)
            else:
                y = torch.nn.functional.scaled_dot_product_attention(q, k, v, attn_mask=None, dropout_p=self.dropout if self.training else 0, is_causal=True)
        else:
            # manual implementation of attention
            att = (q @ k.transpose(-2, -1)) * (1.0 / math.sqrt(k.size(-1)))
            att = att.masked_fill(self.bias[:,:,:T,:T] == 0, float('-inf'))
            att = F.softmax(att, dim=-1)
            att = self.attn_dropout(att)
            y = att @ v # (B, nh, T, T) x (B, nh, T, hs) -> (B, nh, T, hs)
        y = y.transpose(1, 2).contiguous().view(B, T, C) # re-assemble all head outputs side by side

        # output projection
        y = self.resid_dropout(self.c_proj(y))
        return y

class MLP(nn.Module):

    def __init__(self, config):
        super().__init__()
        self.c_fc    = nn.Linear(config.n_embd, 4 * config.n_embd, bias=config.bias)
        self.gelu    = nn.GELU()
        self.c_proj  = nn.Linear(4 * config.n_embd, config.n_embd, bias=config.bias)
        self.dropout = nn.Dropout(config.dropout)

    def forward(self, x):
        x = self.c_fc(x)
        x = self.gelu(x)
        x = self.c_proj(x)
        x = self.dropout(x)
        return x

class BlockJ(nn.Module):

    def __init__(self, config):
        super().__init__()
        self.ln_1 = LayerNorm(config.n_embd, bias=config.bias)
        self.j = LayerNorm(config.n_embd, config.n_embd)
        self.attn = CausalSelfAttention(config)
        self.ln_2 = LayerNorm(config.n_embd, bias=config.bias)
        self.mlp = MLP(config)

    def forward(self, x, attn_mask=None):
        h = x
        x = self.ln_1(x)
        x = h + self.attn(x, attn_mask) + self.j(x)
        x = x + self.mlp(self.ln_2(x))
        return x
        
        
class GPTJXForCausalLM(PreTrainedModel):
    config_class = GPTJXConfig
    base_model_prefix = "transformer"
    is_parallelizable = True
    supports_gradient_checkpointing = True
    _no_split_modules = ["BlockJ"]
    # _skip_keys_device_placement = "past_key_values"
    _supports_flash_attn_2 = True
    _tied_weights_keys = ["lm_head.weight"]
    
    
    def __init__(self, config):
        super().__init__(config)
        assert config.vocab_size is not None
        assert config.block_size is not None
        self.config = config

        self.transformer = nn.ModuleDict(dict(
            wte = nn.Embedding(config.vocab_size, config.n_embd),
            wpe = nn.Embedding(config.block_size, config.n_embd),
            drop = nn.Dropout(config.dropout),
            h = nn.ModuleList([BlockJ(config) for _ in range(config.n_layer)]),
            ln_f = LayerNorm(config.n_embd, bias=config.bias),
        ))
        self.lm_head = nn.Linear(config.n_embd, config.vocab_size, bias=False)
        self.transformer.wte.weight = self.lm_head.weight 

        self.apply(self._init_weights)
        
        for pn, p in self.named_parameters():
            if pn.endswith('c_proj.weight'):
                torch.nn.init.normal_(p, mean=0.0, std=0.02/math.sqrt(2 * config.n_layer))

        print("number of parameters: %.2fM" % (self.get_num_params()/1e6,))

    def get_num_params(self, non_embedding=True):
        """
        Return the number of parameters in the model.
        For non-embedding count (default), the position embeddings get subtracted.
        The token embeddings would too, except due to the parameter sharing these
        params are actually used as weights in the final layer, so we include them.
        """
        n_params = sum(p.numel() for p in self.parameters())
        if non_embedding:
            n_params -= self.transformer.wpe.weight.numel()
        return n_params


    def get_input_embeddings(self):
        return self.wte

    def set_input_embeddings(self, new_embeddings):
        self.wte = new_embeddings

    def forward(self, idx, targets=None, attn_mask= None,  output_hidden_states: Optional[bool] = None, **kwargs):
        device = idx.device
        b, t = idx.size()
        
        assert t <= self.config.block_size, f"Cannot forward sequence of length {t}, block size is only {self.config.block_size}"
        pos = torch.arange(0, t, dtype=torch.long, device=device) # shape (t)

        # forward the GPT model itself
        tok_emb = self.transformer.wte(idx) # token embeddings of shape (b, t, n_embd)
        pos_emb = self.transformer.wpe(pos) # position embeddings of shape (t, n_embd)
        x = self.transformer.drop(tok_emb + pos_emb)
        for block in self.transformer.h:
            x = block(x, attn_mask=attn_mask)
        x = self.transformer.ln_f(x)
        
        # logits = self.lm_head(x)  # logits over the entire sequence, shape (b, t, vocab_size)
        if targets is not None:
            # if we are given some desired targets also calculate the loss
            logits = self.lm_head(x)
            loss = F.cross_entropy(logits.view(-1, logits.size(-1)), targets.view(-1), ignore_index=-100)
        else:
            # inference-time mini-optimization: only forward the lm_head on the very last position
            logits = self.lm_head(x[:, [-1], :]) # note: using list [-1] to preserve the time dim
            loss = None

        return CausalLMOutputWithPast(
            loss=loss,
            logits=logits,
            hidden_states=x if output_hidden_states else None,
            attentions= None,
        )

    def prepare_inputs_for_generation(self, input_ids, attention_mask=None, **kwargs):
        # Default model inputs
        model_inputs = {"idx": input_ids}

        # Add attention mask if provided
        if attention_mask is not None:
            model_inputs["attn_mask"] = attention_mask
            
        return model_inputs
            

    def crop_block_size(self, block_size):
        assert block_size <= self.config.block_size
        self.config.block_size = block_size
        self.transformer.wpe.weight = nn.Parameter(self.transformer.wpe.weight[:block_size])
        for block in self.transformer.h:
            if hasattr(block.attn, 'bias'):
                block.attn.bias = block.attn.bias[:,:,:block_size,:block_size]
                

AutoConfig.register("sabiyarn", GPTJXConfig)
AutoModel.register(GPTJXConfig,GPTJXForCausalLM)
AutoModelForCausalLM.register(GPTJXConfig, GPTJXForCausalLM)