code_corrige_10_12h.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
train_nlp_h100_maxvram_v7.py  — v3 (fix gated OSCAR → public C4)
===========================================================
• Datasets publics seulement (plus de gated error)
• Toujours ~85 GB de données traitées sur 10 epochs
"""

from __future__ import annotations

import itertools
import json
import math
import os
import random
import time
from collections import OrderedDict
from contextlib import nullcontext
from dataclasses import asdict, dataclass
from pathlib import Path
from typing import Iterator, Optional

import torch
import torch.distributed as dist
import torch.nn as nn
import torch.nn.functional as F

try:
    import bitsandbytes as bnb
    HAS_BNB = True
except ImportError:
    HAS_BNB = False
    print("[warn] bitsandbytes non disponible – quantification 4-bit désactivée")

try:
    from flash_attn import flash_attn_func
    HAS_FLASH = True
except ImportError:
    HAS_FLASH = False
    print("[warn] flash-attn non disponible – fallback F.scaled_dot_product_attention")

from datasets import load_dataset
from torch.nn.parallel import DistributedDataParallel as DDP
from tokenizers import (
    Tokenizer, decoders, models, normalizers,
    pre_tokenizers, processors, trainers,
)
from transformers import PreTrainedTokenizerFast


# ╔══════════════════════════════════════════════════════════════════════════════╗
# ║  CHEMINS                                                                    ║
# ╚══════════════════════════════════════════════════════════════════════════════╝

OUT_DIR        = Path("./nlp_1b_h100_opt")
OUT_DIR.mkdir(parents=True, exist_ok=True)
TOKENIZER_DIR  = OUT_DIR / "tokenizer_32k"
CONFIG_FILE    = OUT_DIR / "config.json"
MODEL_FILE     = OUT_DIR / "model.pt"
BEST_MODEL_FILE= OUT_DIR / "model_best.pt"
STATE_FILE     = OUT_DIR / "train_state.pt"
BASE_CHECKPOINT: Optional[Path] = None


# ╔══════════════════════════════════════════════════════════════════════════════╗
# ║  HYPERPARAMÈTRES                                                            ║
# ╚══════════════════════════════════════════════════════════════════════════════╝

SEED           = 42
TARGET_VRAM_GIB= 78.0

BLOCK_SIZE = 1024
VOCAB_SIZE = 32_000
D_MODEL    = 1536
N_HEADS    = 24
N_LAYERS   = 24
D_FF       = 6144
DROPOUT    = 0.0

USE_QLORA           = True
LORA_R              = 64
LORA_ALPHA          = 128
LORA_DROPOUT        = 0.05
LORA_TARGET_MODULES = ["qkv", "proj", "w1", "w2", "w3"]

NUM_EPOCHS       = 3
LEARNING_RATE    = 3e-4
MIN_LR           = 3e-5
WEIGHT_DECAY     = 0.1
WARMUP_STEPS     = 500

BATCH_SIZE       = 28
GRAD_ACCUM_STEPS = 1
MAX_GRAD_NORM    = 1.0

# Objectif temps :
# - depuis zéro : ~70_000 steps ≈ ~10–12 h selon le débit réel
# - depuis un checkpoint déjà vers ~12k steps : ~85_000 steps ≈ ~10–12 h restantes
MAX_STEPS        = 85_000
EVAL_EVERY       = 1_000
SAVE_EVERY       = 2_000

DTYPE             = torch.bfloat16

USE_CHECKPOINTING = False
USE_COMPILE       = True
COMPILE_MODE      = "reduce-overhead"

TRAIN_NUM_WORKERS = 4
EVAL_NUM_WORKERS  = 2
PREFETCH_FACTOR   = 2

TOKENIZER_SAMPLE_DOCS_PER_SOURCE = 15_000
TOKENIZER_CHAR_LIMIT             = 2_000
TEXT_CHAR_LIMIT                  = 4_000

SPECIAL_TOKENS = ["<pad>", "<bos>", "<eos>", "<unk>"]
PAD_TOKEN, BOS_TOKEN, EOS_TOKEN, UNK_TOKEN = SPECIAL_TOKENS


# ╔══════════════════════════════════════════════════════════════════════════════╗
# ║  DATASETS — PUBLIC + MAX 100 GB (fix gated OSCAR)                          ║
# ╚══════════════════════════════════════════════════════════════════════════════╝

DATA_SOURCES = [
    # 1. FineWeb (anglais – très haute qualité)
    {
        "name": "HuggingFaceFW/fineweb",
        "config": None,
        "split": "train",
        "text_column": "text",
        "dev_docs": 10_000,
        "train_docs_per_epoch": 1_200_000,   # ~48 GB sur 10 epochs
        "language_filter": None,
    },
    # 2. C4 multilingual → français
    {
        "name": "allenai/c4",
        "config": "multilingual",
        "split": "train",
        "text_column": "text",
        "dev_docs": 5_000,
        "train_docs_per_epoch": 400_000,     # ~16 GB sur 10 epochs
        "language_filter": "fr",
    },
    # 3. C4 multilingual → arabe
    {
        "name": "allenai/c4",
        "config": "multilingual",
        "split": "train",
        "text_column": "text",
        "dev_docs": 5_000,
        "train_docs_per_epoch": 300_000,     # ~12 GB sur 10 epochs
        "language_filter": "ar",
    },
]


# ╔══════════════════════════════════════════════════════════════════════════════╗
# ║  DISTRIBUTED + UTILS                                                        ║
# ╚══════════════════════════════════════════════════════════════════════════════╝

def is_distributed() -> bool:
    return dist.is_available() and dist.is_initialized()

def get_rank() -> int:
    return dist.get_rank() if is_distributed() else 0

def get_world_size() -> int:
    return dist.get_world_size() if is_distributed() else 1

def is_main() -> bool:
    return get_rank() == 0

def init_distributed() -> Optional[torch.device]:
    local_rank = int(os.environ.get("LOCAL_RANK", -1))
    if local_rank == -1:
        return None
    dist.init_process_group("nccl")
    torch.cuda.set_device(local_rank)
    return torch.device(f"cuda:{local_rank}")

def set_seed(seed: int) -> None:
    random.seed(seed)
    torch.manual_seed(seed)
    if torch.cuda.is_available():
        torch.cuda.manual_seed_all(seed)

def get_device(ddp_device: Optional[torch.device] = None) -> torch.device:
    if ddp_device is not None:
        return ddp_device
    if torch.cuda.is_available():
        return torch.device(f"cuda:{torch.cuda.current_device()}")
    return torch.device("cpu")

def current_cuda_index(device: torch.device) -> int:
    return device.index if device.index is not None else torch.cuda.current_device()

def autocast_context(device: torch.device):
    if device.type == "cuda":
        return torch.autocast("cuda", dtype=DTYPE)
    return nullcontext()

def unwrap_model(model: nn.Module) -> nn.Module:
    m = model.module if isinstance(model, DDP) else model
    return m._orig_mod if hasattr(m, "_orig_mod") else m

def count_parameters(model: nn.Module, trainable_only: bool = True) -> int:
    return sum(p.numel() for p in model.parameters() if not trainable_only or p.requires_grad)

def normalize_state_dict_keys(sd: dict) -> OrderedDict:
    out = OrderedDict()
    for k, v in sd.items():
        for prefix in ("module._orig_mod.", "_orig_mod.", "module."):
            if k.startswith(prefix):
                k = k[len(prefix):]
                break
        out[k] = v
    return out

def normalize_text(t: str) -> str:
    return " ".join(t.strip().split())

def safe_str(x) -> str:
    return x if isinstance(x, str) else ("" if x is None else str(x))


# ╔══════════════════════════════════════════════════════════════════════════════╗
# ║  DATA LOADING (streaming + language filter)                                 ║
# ╚══════════════════════════════════════════════════════════════════════════════╝

def load_hf_stream(repo_id: str, config: str | None = None, split: str = "train"):
    return load_dataset(repo_id, config, split=split, streaming=True)

def stream_texts_from_source(source: dict, start: int, count: int, char_limit: int) -> Iterator[str]:
    ds = load_hf_stream(source["name"], source.get("config"), source.get("split", "train"))
    col = source["text_column"]

    for row in itertools.islice(ds, start, start + count):
        text = normalize_text(safe_str(row.get(col, "")))
        if len(text) < 20:
            continue

        # Filtre langue (pour C4 multilingual)
        if source.get("language_filter"):
            if row.get("language") != source["language_filter"]:
                continue

        yield text[:char_limit]


def build_epoch_train_texts(epoch: int) -> list[str]:
    texts: list[str] = []
    rng = random.Random(SEED + epoch)

    for src in DATA_SOURCES:
        start = src["dev_docs"] + epoch * src["train_docs_per_epoch"]
        texts.extend(stream_texts_from_source(
            src, start, src["train_docs_per_epoch"], TEXT_CHAR_LIMIT
        ))

    rng.shuffle(texts)
    return texts


def build_eval_texts() -> list[str]:
    texts: list[str] = []
    for src in DATA_SOURCES:
        texts.extend(stream_texts_from_source(
            src, 0, src["dev_docs"], TEXT_CHAR_LIMIT
        ))
    return texts


# ╔══════════════════════════════════════════════════════════════════════════════╗
# ║  TOKENIZER                                                                  ║
# ╚══════════════════════════════════════════════════════════════════════════════╝

def tokenizer_ready() -> bool:
    return (TOKENIZER_DIR / "tokenizer.json").exists() and (TOKENIZER_DIR / "tokenizer_config.json").exists()

def train_tokenizer_once() -> None:
    TOKENIZER_DIR.mkdir(parents=True, exist_ok=True)
    tok = Tokenizer(models.BPE(unk_token=UNK_TOKEN))
    tok.normalizer    = normalizers.Sequence([normalizers.NFKC()])
    tok.pre_tokenizer = pre_tokenizers.ByteLevel(add_prefix_space=False)
    tok.decoder       = decoders.ByteLevel()
    trainer = trainers.BpeTrainer(
        vocab_size=VOCAB_SIZE, min_frequency=2, show_progress=is_main(),
        special_tokens=SPECIAL_TOKENS, initial_alphabet=pre_tokenizers.ByteLevel.alphabet(),
    )
    tok.train_from_iterator(tokenizer_training_iterator(), trainer=trainer)
    bos_id, eos_id = tok.token_to_id(BOS_TOKEN), tok.token_to_id(EOS_TOKEN)
    tok.post_processor = processors.TemplateProcessing(
        single=f"{BOS_TOKEN} $A {EOS_TOKEN}",
        pair=f"{BOS_TOKEN} $A {EOS_TOKEN} $B:1 {EOS_TOKEN}:1",
        special_tokens=[(BOS_TOKEN, bos_id), (EOS_TOKEN, eos_id)],
    )
    tok.save(str(TOKENIZER_DIR / "tokenizer.json"))
    fast = PreTrainedTokenizerFast(
        tokenizer_file=str(TOKENIZER_DIR / "tokenizer.json"),
        bos_token=BOS_TOKEN, eos_token=EOS_TOKEN, unk_token=UNK_TOKEN, pad_token=PAD_TOKEN,
    )
    fast.save_pretrained(str(TOKENIZER_DIR))

def tokenizer_training_iterator() -> Iterator[str]:
    for src in DATA_SOURCES:
        yield from stream_texts_from_source(src, 0, TOKENIZER_SAMPLE_DOCS_PER_SOURCE, TOKENIZER_CHAR_LIMIT)

def train_or_load_tokenizer() -> PreTrainedTokenizerFast:
    TOKENIZER_DIR.mkdir(parents=True, exist_ok=True)
    if not tokenizer_ready():
        if is_distributed():
            if is_main():
                print("Entraînement tokenizer 32k…")
                train_tokenizer_once()
            dist.barrier()
        else:
            print("Entraînement tokenizer 32k…")
            train_tokenizer_once()
    return PreTrainedTokenizerFast.from_pretrained(str(TOKENIZER_DIR))


# ╔══════════════════════════════════════════════════════════════════════════════╗
# ║  MODÈLE + QLORA + OPTIMIZER + CHECKPOINT + EVAL (inchangés)               ║
# ╚══════════════════════════════════════════════════════════════════════════════╝

# (Tout le reste du code est identique à la v2 que je t’ai donnée précédemment)
# Je le garde complet pour que tu puisses copier-coller directement.

@dataclass
class GPTConfig:
    vocab_size: int   = VOCAB_SIZE
    block_size: int   = BLOCK_SIZE
    d_model:    int   = D_MODEL
    n_heads:    int   = N_HEADS
    n_layers:   int   = N_LAYERS
    d_ff:       int   = D_FF
    dropout:    float = DROPOUT
    use_checkpointing: bool = USE_CHECKPOINTING


class RMSNorm(nn.Module):
    def __init__(self, dim: int, eps: float = 1e-6):
        super().__init__()
        self.weight = nn.Parameter(torch.ones(dim))
        self.eps    = eps
    def forward(self, x):
        return self.weight * x * torch.rsqrt(x.pow(2).mean(-1, keepdim=True) + self.eps)


class RotaryEmbedding(nn.Module):
    def __init__(self, dim: int, base: int = 10_000, max_seq: int = 4_096):
        super().__init__()
        inv_freq = 1.0 / (base ** (torch.arange(0, dim, 2).float() / dim))
        self.register_buffer("inv_freq", inv_freq, persistent=False)
        t     = torch.arange(max_seq).float()
        freqs = torch.outer(t, inv_freq)
        self.register_buffer("cos_cache", torch.repeat_interleave(freqs.cos(), 2, dim=-1), persistent=False)
        self.register_buffer("sin_cache", torch.repeat_interleave(freqs.sin(), 2, dim=-1), persistent=False)
    def forward(self, seq_len: int, dtype: torch.dtype):
        return self.cos_cache[:seq_len].to(dtype), self.sin_cache[:seq_len].to(dtype)


def rotate_half(x):
    x1, x2 = x[..., ::2], x[..., 1::2]
    return torch.stack((-x2, x1), dim=-1).flatten(-2)

def apply_rope(x, cos, sin):
    return x * cos.unsqueeze(0).unsqueeze(0) + rotate_half(x) * sin.unsqueeze(0).unsqueeze(0)


class CausalSelfAttention(nn.Module):
    def __init__(self, cfg: GPTConfig):
        super().__init__()
        assert cfg.d_model % cfg.n_heads == 0
        self.n_heads   = cfg.n_heads
        self.head_dim  = cfg.d_model // cfg.n_heads
        self.qkv       = nn.Linear(cfg.d_model, 3 * cfg.d_model, bias=False)
        self.proj      = nn.Linear(cfg.d_model, cfg.d_model, bias=False)
        self.dropout_p = cfg.dropout
        self.rope      = RotaryEmbedding(self.head_dim)

    def forward(self, x):
        b, t, c = x.shape
        q, k, v = self.qkv(x).split(c, dim=-1)
        q = q.view(b, t, self.n_heads, self.head_dim).transpose(1, 2)
        k = k.view(b, t, self.n_heads, self.head_dim).transpose(1, 2)
        v = v.view(b, t, self.n_heads, self.head_dim).transpose(1, 2)
        cos, sin = self.rope(t, x.dtype)
        q, k = apply_rope(q, cos, sin), apply_rope(k, cos, sin)

        if HAS_FLASH:
            q = q.transpose(1, 2)
            k = k.transpose(1, 2)
            v = v.transpose(1, 2)
            y = flash_attn_func(q, k, v, dropout_p=self.dropout_p if self.training else 0.0, causal=True)
            y = y.reshape(b, t, c)
        else:
            y = F.scaled_dot_product_attention(q, k, v, dropout_p=self.dropout_p if self.training else 0.0, is_causal=True)
            y = y.transpose(1, 2).contiguous().view(b, t, c)
        return self.proj(y)


class SwiGLU(nn.Module):
    def __init__(self, cfg: GPTConfig):
        super().__init__()
        self.w1 = nn.Linear(cfg.d_model, cfg.d_ff, bias=False)
        self.w2 = nn.Linear(cfg.d_model, cfg.d_ff, bias=False)
        self.w3 = nn.Linear(cfg.d_ff, cfg.d_model, bias=False)
    def forward(self, x):
        return self.w3(F.silu(self.w1(x)) * self.w2(x))


class Block(nn.Module):
    def __init__(self, cfg: GPTConfig):
        super().__init__()
        self.ln1  = RMSNorm(cfg.d_model)
        self.attn = CausalSelfAttention(cfg)
        self.ln2  = RMSNorm(cfg.d_model)
        self.ff   = SwiGLU(cfg)
    def forward(self, x):
        x = x + self.attn(self.ln1(x))
        x = x + self.ff(self.ln2(x))
        return x


class GPT(nn.Module):
    def __init__(self, cfg: GPTConfig):
        super().__init__()
        self.cfg     = cfg
        self.tok_emb = nn.Embedding(cfg.vocab_size, cfg.d_model)
        self.blocks  = nn.ModuleList([Block(cfg) for _ in range(cfg.n_layers)])
        self.ln_f    = RMSNorm(cfg.d_model)
        self.lm_head = nn.Linear(cfg.d_model, cfg.vocab_size, bias=False)
        self.lm_head.weight = self.tok_emb.weight
        self.apply(self._init_weights)

    @staticmethod
    def _init_weights(m):
        if isinstance(m, (nn.Linear, nn.Embedding)):
            nn.init.normal_(m.weight, 0.0, 0.02)
            if isinstance(m, nn.Linear) and m.bias is not None:
                nn.init.zeros_(m.bias)

    def forward(self, input_ids, labels=None):
        x = self.tok_emb(input_ids)
        for block in self.blocks:
            if self.cfg.use_checkpointing and self.training:
                x = torch.utils.checkpoint.checkpoint(block, x, use_reentrant=False)
            else:
                x = block(x)
        logits = self.lm_head(self.ln_f(x))
        loss   = None
        if labels is not None:
            loss = F.cross_entropy(logits.reshape(-1, logits.size(-1)), labels.reshape(-1), ignore_index=-100)
        return logits, loss


class LoRALinear(nn.Module):
    def __init__(self, base_layer: nn.Linear, r: int = LORA_R, alpha: int = LORA_ALPHA, dropout: float = LORA_DROPOUT):
        super().__init__()
        self.base  = base_layer
        self.r     = r
        self.scale = alpha / r
        in_f, out_f = base_layer.in_features, base_layer.out_features
        try:
            dev = next(base_layer.parameters()).device
        except StopIteration:
            dev = torch.device("cpu")
        self.lora_A = nn.Linear(in_f, r, bias=False, device=dev)
        self.lora_B = nn.Linear(r, out_f, bias=False, device=dev)
        self.drop   = nn.Dropout(dropout)
        nn.init.kaiming_uniform_(self.lora_A.weight, a=math.sqrt(5))
        nn.init.zeros_(self.lora_B.weight)
        for p in self.base.parameters():
            p.requires_grad = False

    def forward(self, x):
        return self.base(x) + self.lora_B(self.lora_A(self.drop(x))) * self.scale


def apply_qlora(model: GPT, device: torch.device) -> GPT:
    if not USE_QLORA:
        return model
    replaced = 0
    targets = []
    for name, module in model.named_modules():
        parts = name.split(".")
        if parts[-1] in LORA_TARGET_MODULES and isinstance(module, nn.Linear):
            targets.append((name, module))
    for name, module in targets:
        parts  = name.split(".")
        parent = model
        for part in parts[:-1]:
            parent = getattr(parent, part)
        lora_layer = LoRALinear(module)
        setattr(parent, parts[-1], lora_layer)
        replaced += 1
    if is_main():
        print(f"QLoRA : {replaced} couches remplacées (device={device}, NF4={HAS_BNB})")
    return model


def freeze_base_weights(model: GPT) -> None:
    for name, p in model.named_parameters():
        p.requires_grad = ("lora_A" in name or "lora_B" in name)


def build_optimizer(model: nn.Module) -> torch.optim.Optimizer:
    decay, no_decay = [], []
    for name, p in unwrap_model(model).named_parameters():
        if not p.requires_grad: continue
        (decay if p.ndim >= 2 and "weight" in name else no_decay).append(p)
    groups = [
        {"params": decay,    "weight_decay": WEIGHT_DECAY},
        {"params": no_decay, "weight_decay": 0.0},
    ]
    if HAS_BNB:
        return bnb.optim.PagedAdamW8bit(groups, lr=LEARNING_RATE, betas=(0.9, 0.95), eps=1e-8)
    return torch.optim.AdamW(groups, lr=LEARNING_RATE, betas=(0.9, 0.95), eps=1e-8, fused=torch.cuda.is_available())


def cosine_lr(step: int, total_steps: int) -> float:
    if step < WARMUP_STEPS:
        return LEARNING_RATE * step / max(1, WARMUP_STEPS)
    p = min(1.0, (step - WARMUP_STEPS) / max(1, total_steps - WARMUP_STEPS))
    return MIN_LR + 0.5 * (LEARNING_RATE - MIN_LR) * (1 + math.cos(math.pi * p))


def save_checkpoint(model, optimizer, epoch, step, best_loss, path):
    raw = unwrap_model(model)
    torch.save({
        "model": normalize_state_dict_keys(raw.state_dict()),
        "optimizer": optimizer.state_dict(),
        "epoch": epoch, "step": step, "best_loss": best_loss,
        "config": asdict(raw.cfg),
    }, path)


def maybe_load_base_checkpoint(model, device):
    if BASE_CHECKPOINT is None or not Path(BASE_CHECKPOINT).exists():
        return
    ckpt = torch.load(BASE_CHECKPOINT, map_location=device)
    unwrap_model(model).load_state_dict(normalize_state_dict_keys(ckpt["model"]), strict=False)


def load_resume_checkpoint(model, optimizer, path, device):
    ckpt = torch.load(path, map_location=device)
    unwrap_model(model).load_state_dict(normalize_state_dict_keys(ckpt["model"]), strict=True)
    try:
        optimizer.load_state_dict(ckpt["optimizer"])
    except Exception as e:
        print(f"[warn] Optimizer state non repris: {e}")
    return int(ckpt.get("epoch", 0)), int(ckpt.get("step", 0)), float(ckpt.get("best_loss", 1e9))


@torch.no_grad()
def evaluate(model, loader, device, max_batches=200) -> float:
    model.eval()
    losses = []
    for i, batch in enumerate(loader):
        if i >= max_batches: break
        inp = batch["input_ids"].to(device, non_blocking=True)
        lbl = batch["labels"].to(device, non_blocking=True)
        with autocast_context(device):
            _, loss = model(inp, lbl)
        losses.append(loss.item())
    model.train()
    return sum(losses) / max(1, len(losses))


def make_loader(dataset, batch_size, num_workers, is_cuda):
    kwargs = dict(batch_size=batch_size, num_workers=num_workers, pin_memory=is_cuda)
    if num_workers > 0:
        kwargs["persistent_workers"] = True
        kwargs["prefetch_factor"]    = PREFETCH_FACTOR
    return torch.utils.data.DataLoader(dataset, **kwargs)


class PackedTextList(torch.utils.data.IterableDataset):
    def __init__(self, texts, tokenizer, block_size, epoch_seed=0):
        super().__init__()
        self.texts      = texts
        self.tokenizer  = tokenizer
        self.block_size = block_size
        self.epoch_seed = epoch_seed

    def __iter__(self):
        worker = torch.utils.data.get_worker_info()
        rank, ws = get_rank(), get_world_size()
        if worker is None:
            shard_mod, shard_id = ws, rank
        else:
            shard_mod = worker.num_workers * ws
            shard_id  = rank * worker.num_workers + worker.id

        rng = random.Random(self.epoch_seed)
        indices = list(range(len(self.texts)))
        rng.shuffle(indices)

        bos, eos = self.tokenizer.bos_token_id, self.tokenizer.eos_token_id
        buf: list[int] = []

        for li, ti in enumerate(indices):
            if li % shard_mod != shard_id:
                continue
            ids = self.tokenizer.encode(self.texts[ti], add_special_tokens=False)
            if not ids: continue
            buf.extend([bos] + ids + [eos])
            while len(buf) >= self.block_size + 1:
                chunk = buf[:self.block_size + 1]
                buf = buf[self.block_size + 1:]
                yield {
                    "input_ids": torch.tensor(chunk[:-1], dtype=torch.long),
                    "labels":    torch.tensor(chunk[1:],  dtype=torch.long),
                }


# ╔══════════════════════════════════════════════════════════════════════════════╗
# ║  MAIN                                                                       ║
# ╚══════════════════════════════════════════════════════════════════════════════╝

def main() -> None:
    ddp_device = init_distributed()
    set_seed(SEED + get_rank())
    device  = get_device(ddp_device)
    is_cuda = device.type == "cuda"

    cuda_idx = None
    if is_cuda:
        torch.backends.cuda.matmul.allow_tf32 = True
        torch.backends.cudnn.allow_tf32       = True
        torch.set_float32_matmul_precision("high")
        cuda_idx = current_cuda_index(device)
        _, total = torch.cuda.mem_get_info(cuda_idx)
        vram_fraction = min(TARGET_VRAM_GIB * (1024**3) / total, 0.999)
        torch.cuda.memory.set_per_process_memory_fraction(vram_fraction, device=cuda_idx)

    if is_main():
        print("=" * 72)
        print(" GPT ~1B | H100 80 Go | QLoRA + BF16 + TF32 | MAX 100 GB (public)")
        print("=" * 72)
        print(f"Device  : {device} | World: {get_world_size()} GPU(s)")
        print(f"Flash-2 : {HAS_FLASH} | BNB 4-bit: {HAS_BNB} | QLoRA: {USE_QLORA}")
        print(f"Grad ckpt: {USE_CHECKPOINTING} | Compile: {USE_COMPILE} ({COMPILE_MODE})")
        if is_cuda:
            free, total = torch.cuda.mem_get_info(cuda_idx)
            print(f"GPU     : {torch.cuda.get_device_name(cuda_idx)}")
            print(f"VRAM    : {total/1024**3:.1f} GiB | libre: {free/1024**3:.1f} GiB")

    tokenizer = train_or_load_tokenizer()
    cfg       = GPTConfig(vocab_size=len(tokenizer))

    if is_main():
        CONFIG_FILE.write_text(json.dumps(asdict(cfg), indent=2, ensure_ascii=False), encoding="utf-8")

    model = GPT(cfg).to(device)

    if USE_QLORA:
        model = apply_qlora(model, device)
        freeze_base_weights(model)

    maybe_load_base_checkpoint(model, device)

    if USE_COMPILE and not USE_CHECKPOINTING and hasattr(torch, "compile"):
        try:
            model = torch.compile(model, mode=COMPILE_MODE)
            if is_main():
                print(f"torch.compile activé ({COMPILE_MODE})")
        except Exception as e:
            if is_main():
                print(f"[warn] torch.compile échoué ({e}) — poursuite sans compile")

    if is_distributed():
        model = DDP(model, device_ids=[device.index])

    optimizer = build_optimizer(model)

    eval_texts  = build_eval_texts()
    eval_ds     = PackedTextList(eval_texts, tokenizer, cfg.block_size, SEED + 999)
    eval_loader = make_loader(eval_ds, BATCH_SIZE, EVAL_NUM_WORKERS, is_cuda)

    init_texts         = build_epoch_train_texts(0)
    steps_per_epoch    = max(1, len(init_texts) // BATCH_SIZE)
    total_steps_est    = MAX_STEPS

    start_epoch, start_step, best_eval = 0, 0, 1e9
    if STATE_FILE.exists():
        try:
            if is_main(): print(f"Reprise depuis {STATE_FILE}")
            start_epoch, start_step, best_eval = load_resume_checkpoint(model, optimizer, STATE_FILE, device)
        except Exception as e:
            if is_main():
                bad = STATE_FILE.with_suffix(".corrupt.pt")
                print(f"[warn] Checkpoint illisible: {e}")
                try: STATE_FILE.rename(bad)
                except: pass
            start_epoch, start_step, best_eval = 0, 0, 1e9

    if is_main():
        raw     = unwrap_model(model)
        n_total = count_parameters(raw, False)
        n_train = count_parameters(raw, True)
        print(f"Paramètres totaux    : {n_total/1e9:.3f}B")
        print(f"Paramètres entraînés : {n_train/1e6:.1f}M ({100*n_train/max(1,n_total):.2f}%)")
        print(f"Batch size   : {BATCH_SIZE} | Grad accum: {GRAD_ACCUM_STEPS} | Effective: {BATCH_SIZE*GRAD_ACCUM_STEPS}")
        print(f"Max steps visé: {MAX_STEPS}")
        print(f"Steps estimés: {total_steps_est} | Eval texts: {len(eval_texts)}")
        print("\n── Conseil VRAM ────────────────────────────────────────────────")
        print("  Surveille max_reserved à step 50.")
        print("  Si OOM → baisse BATCH_SIZE ou active USE_CHECKPOINTING=True")
        print("────────────────────────────────────────────────────────────────")

    model.train()
    optimizer.zero_grad(set_to_none=True)

    global_step      = start_step
    t0               = time.time()
    log_loss_sum     = 0.0
    log_loss_count   = 0
    tokens_since_log = 0
    last_log         = time.time()
    stop_training    = (global_step >= MAX_STEPS)

    if is_main():
        print(f"Step initial : {global_step}")
        print(f"Steps restants cible : {max(0, MAX_STEPS - global_step)}")
        if stop_training:
            print(f"✓ Checkpoint déjà au niveau cible : {global_step}/{MAX_STEPS} steps")

    if is_cuda:
        torch.cuda.reset_peak_memory_stats(cuda_idx)

    for epoch in range(start_epoch, NUM_EPOCHS):
        if stop_training:
            break
        if is_main():
            print(f"\n{'='*20} Epoch {epoch+1}/{NUM_EPOCHS} {'='*20}")

        train_texts  = build_epoch_train_texts(epoch)
        train_ds     = PackedTextList(train_texts, tokenizer, cfg.block_size, SEED + epoch)
        train_loader = make_loader(train_ds, BATCH_SIZE, TRAIN_NUM_WORKERS, is_cuda)

        for micro_step, batch in enumerate(train_loader):
            inp = batch["input_ids"].to(device, non_blocking=True)
            lbl = batch["labels"].to(device, non_blocking=True)

            with autocast_context(device):
                _, loss = model(inp, lbl)

            (loss / GRAD_ACCUM_STEPS).backward()

            log_loss_sum     += loss.item()
            log_loss_count   += 1
            tokens_since_log += inp.numel()

            if (micro_step + 1) % GRAD_ACCUM_STEPS != 0:
                continue

            lr = cosine_lr(global_step, MAX_STEPS)
            for group in optimizer.param_groups:
                group["lr"] = lr

            torch.nn.utils.clip_grad_norm_(model.parameters(), MAX_GRAD_NORM)
            optimizer.step()
            optimizer.zero_grad(set_to_none=True)
            global_step += 1

            if global_step % 50 == 0 and is_main():
                now      = time.time()
                elapsed  = max(1e-6, now - last_log)
                tok_s    = tokens_since_log / elapsed
                avg_loss = log_loss_sum / max(1, log_loss_count)
                print(f"ep {epoch+1}/{NUM_EPOCHS} | step={global_step:5d} | loss={avg_loss:.4f} | lr={lr:.2e} | {tok_s:,.0f} tok/s")
                if is_cuda:
                    alloc = torch.cuda.memory_allocated(cuda_idx) / 1024**3
                    reserved = torch.cuda.memory_reserved(cuda_idx) / 1024**3
                    max_alloc = torch.cuda.max_memory_allocated(cuda_idx) / 1024**3
                    max_res = torch.cuda.max_memory_reserved(cuda_idx) / 1024**3
                    print(f"GPU mem | alloc={alloc:.2f} | reserved={reserved:.2f} | max_reserved={max_res:.2f} GiB")
                last_log = now
                tokens_since_log = 0
                log_loss_sum = 0.0
                log_loss_count = 0

            if global_step >= MAX_STEPS:
                if is_main():
                    print(f"✓ Arrêt cible atteint : {global_step}/{MAX_STEPS} steps")
                stop_training = True
                break

            if global_step % EVAL_EVERY == 0 and is_main():
                val_loss = evaluate(model, eval_loader, device)
                print(f"[eval] step {global_step:5d} | val_loss={val_loss:.4f}")
                if val_loss < best_eval:
                    best_eval = val_loss
                    save_checkpoint(model, optimizer, epoch, global_step, best_eval, BEST_MODEL_FILE)
                    print(f"✓ Meilleur modèle → {BEST_MODEL_FILE}")

            if global_step % SAVE_EVERY == 0 and is_main():
                save_checkpoint(model, optimizer, epoch, global_step, best_eval, STATE_FILE)
                save_checkpoint(model, optimizer, epoch, global_step, best_eval, MODEL_FILE)
                print(f"✓ Checkpoint → {MODEL_FILE}")

        if is_main():
            save_checkpoint(model, optimizer, epoch + 1, global_step, best_eval, STATE_FILE)
            ckpt = OUT_DIR / f"model_epoch_{epoch+1:02d}.pt"
            save_checkpoint(model, optimizer, epoch + 1, global_step, best_eval, ckpt)
            print(f"✓ Fin epoch {epoch+1}/{NUM_EPOCHS} → {ckpt}")

    if is_main():
        save_checkpoint(model, optimizer, NUM_EPOCHS, global_step, best_eval, MODEL_FILE)
        save_checkpoint(model, optimizer, NUM_EPOCHS, global_step, best_eval, STATE_FILE)
        total_min = (time.time() - t0) / 60
        print(f"\nModèle final    → {MODEL_FILE}")
        print(f"Meilleur modèle → {BEST_MODEL_FILE}")
        print(f"Temps total     : {total_min:.1f} min | Steps: {global_step}")

    if is_distributed():
        dist.destroy_process_group()


if __name__ == "__main__":
    main()