[Doc][3/N] Reorganize Serving section (#11766)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

docs/source/models/extensions/runai_model_streamer.md

@@ -0,0 +1,53 @@
+(runai-model-streamer)=
+
+# Loading models with Run:ai Model Streamer
+
+Run:ai Model Streamer is a library to read tensors in concurrency, while streaming it to GPU memory.
+Further reading can be found in [Run:ai Model Streamer Documentation](https://github.com/run-ai/runai-model-streamer/blob/master/docs/README.md).
+
+vLLM supports loading weights in Safetensors format using the Run:ai Model Streamer.
+You first need to install vLLM RunAI optional dependency:
+
+```console
+$ pip3 install vllm[runai]
+```
+
+To run it as an OpenAI-compatible server, add the `--load-format runai_streamer` flag:
+
+```console
+$ vllm serve /home/meta-llama/Llama-3.2-3B-Instruct --load-format runai_streamer
+```
+
+To run model from AWS S3 object store run:
+
+```console
+$ vllm serve s3://core-llm/Llama-3-8b --load-format runai_streamer
+```
+
+To run model from a S3 compatible object store run:
+
+```console
+$ RUNAI_STREAMER_S3_USE_VIRTUAL_ADDRESSING=0 AWS_EC2_METADATA_DISABLED=true AWS_ENDPOINT_URL=https://storage.googleapis.com vllm serve s3://core-llm/Llama-3-8b --load-format runai_streamer
+```
+
+## Tunable parameters
+
+You can tune parameters using `--model-loader-extra-config`:
+
+You can tune `concurrency` that controls the level of concurrency and number of OS threads reading tensors from the file to the CPU buffer.
+For reading from S3, it will be the number of client instances the host is opening to the S3 server.
+
+```console
+$ vllm serve /home/meta-llama/Llama-3.2-3B-Instruct --load-format runai_streamer --model-loader-extra-config '{"concurrency":16}'
+```
+
+You can control the size of the CPU Memory buffer to which tensors are read from the file, and limit this size.
+You can read further about CPU buffer memory limiting [here](https://github.com/run-ai/runai-model-streamer/blob/master/docs/src/env-vars.md#runai_streamer_memory_limit).
+
+```console
+$ vllm serve /home/meta-llama/Llama-3.2-3B-Instruct --load-format runai_streamer --model-loader-extra-config '{"memory_limit":5368709120}'
+```
+
+```{note}
+For further instructions about tunable parameters and additional parameters configurable through environment variables, read the [Environment Variables Documentation](https://github.com/run-ai/runai-model-streamer/blob/master/docs/src/env-vars.md).
+```