feat: add coordinated checkpoint prefetch for network filesystem loading (#20843)

docs/advanced_features/server_arguments.md

@@ -510,6 +510,8 @@ Please consult the documentation below and [server_args.py](https://github.com/s
 | --- | --- | --- | --- |
 | `--custom-weight-loader` | The custom dataloader which used to update the model. Should be set with a valid import path, such as my_package.weight_load_func | `None` | List[str] |
 | `--weight-loader-disable-mmap` | Disable mmap while loading weight using safetensors. | `False` | bool flag (set to enable) |
+| `--weight-loader-prefetch-checkpoints` | Prefetch checkpoint files into OS page cache before loading. Each rank prefetches a fraction of the shards in a background thread, reducing total network I/O on shared filesystems (NFS/Lustre) from N\*checkpoint to 1\*checkpoint. Recommended for models on network storage. | `False` | bool flag (set to enable) |
+| `--weight-loader-prefetch-num-threads` | Number of threads per rank for checkpoint prefetching. | `4` | Type: int |
 | `--remote-instance-weight-loader-seed-instance-ip` | The ip of the seed instance for loading weights from remote instance. | `None` | Type: str |
 | `--remote-instance-weight-loader-seed-instance-service-port` | The service port of the seed instance for loading weights from remote instance. | `None` | Type: int |
 | `--remote-instance-weight-loader-send-weights-group-ports` | The communication group ports for loading weights from remote instance. | `None` | Type: JSON list |

docs/references/environment_variables.md

@@ -20,6 +20,7 @@ SGLang supports various environment variables that can be used to configure its
 | `SGLANG_REQ_WAITING_TIMEOUT`              | Timeout (in seconds) for requests waiting in the queue before being scheduled                                                    | `-1`                         |
 | `SGLANG_REQ_RUNNING_TIMEOUT`              | Timeout (in seconds) for requests running in the decode batch                                                                    | `-1`                         |
 | `SGLANG_CACHE_DIR`                        | Cache directory for model weights and other data | `~/.cache/sglang` |
+| `SGLANG_PREFETCH_BLOCK_SIZE_MB`           | Block size (in MB) for sequential checkpoint prefetch reads that warm the OS page cache before workers load weights via mmap | `16` |
 
 ## Performance Tuning