[HiCache][HA 1/N] Support HiCache storage runtime attach/detach (#15892)

docs/advanced_features/hicache.rst

@@ -6,3 +6,4 @@ Hierarchical KV Caching (HiCache)
 
    hicache_best_practices.md
    hicache_design.md
+   hicache_storage_runtime_attach_detach.md

docs/advanced_features/hicache_best_practices.md

@@ -19,6 +19,10 @@ SGLang HiCache extends the traditional RadixAttention with a three-tier hierarch
 --hicache-storage-backend             # Optional storage backend (e.g., hf3fs, mooncake, etc.)
 ```
 
+Notes:
+
+- Besides configuring `--hicache-storage-backend` at startup, SGLang also supports **runtime attach/detach** of the HiCache storage backend (no restart required) via HTTP admin endpoints. See [Runtime Attach/Detach HiCache Storage Backend](hicache_storage_runtime_attach_detach.md).
+
 ## Key Configurations with Storage Backends Enabled
 
 ### Memory Layout Optimization

docs/advanced_features/hicache_storage_runtime_attach_detach.md

@@ -0,0 +1,132 @@
+# Runtime Attach/Detach HiCache Storage Backend (No Restart)
+
+This document explains how to **dynamically attach/detach the HiCache L3 storage backend at runtime** (e.g., `mooncake` / `hf3fs` / `nixl` / `file` / `aibrix` / `eic`) while **SGLang is already running and serving traffic**, without restarting the process.
+
+For safety and consistency, the current implementation **strictly requires** these operations to happen only when the service is **idle**:
+
+- **No running requests**
+- **No waiting/queued requests**
+
+If the idle condition is not met, the API will fail fast (HTTP 400) and **will not modify** the current service state.
+
+---
+
+## 1. Background and implementation overview
+
+### 1.1 Architecture / control path
+
+The control path is:
+
+1. **HTTP Server** (`python/sglang/srt/entrypoints/http_server.py`)
+   - Exposes `PUT /hicache/storage-backend`, `DELETE /hicache/storage-backend`, `GET /hicache/storage-backend`
+2. **TokenizerManager** (`python/sglang/srt/managers/tokenizer_communicator_mixin.py`)
+   - Sends the request to the Scheduler via `_Communicator`
+3. **Scheduler** (`python/sglang/srt/managers/scheduler.py`)
+   - Performs a **strict idle check**
+   - Calls `tree_cache.attach_storage_backend(...)` / `detach_storage_backend(...)`
+4. **HiRadixCache** (`python/sglang/srt/mem_cache/hiradix_cache.py`)
+   - Parses `hicache_storage_backend_extra_config_json` (supports both backend config and prefetch knobs)
+   - Calls `cache_controller.attach_storage_backend(...)` / `detach_storage_backend(...)`
+5. **HiCacheController** (`python/sglang/srt/managers/cache_controller.py`)
+   - Creates/destroys the storage backend instance (via `StorageBackendFactory`)
+   - Starts/stops backend background threads at runtime (prefetch/backup)
+
+---
+
+## 2. Idle-state requirement (strict)
+
+The Scheduler uses a stricter `_is_idle_for_hicache_storage_op()`:
+
+- `_is_no_request()` is true (covers running/overlap/pp/disagg and other active states)
+- `waiting_queue` is empty
+- `grammar_queue` is empty (if the grammar backend is enabled)
+
+If the condition is not met, attach/detach returns an error like:
+
+- `Reject attach: scheduler is not idle. #queue-req=... #running-req=...`
+
+> Tip: before switching, drain upstream traffic and wait for the server to become idle, then call attach/detach.
+
+### 2.1 DP (data parallel) semantics
+
+When `dp_size > 1`, the tokenizer dispatches the request to **all DP scheduler instances** and aggregates their responses:
+
+- The final `success` is **true only if all DP ranks return success**
+- The final `message` concatenates messages from all DP ranks
+
+This is intended to prevent “silent partial success”, but it also means you may see:
+
+- Overall **failure** even though **some ranks already succeeded**
+
+Currently there is **no automatic partial rollback** across DP ranks (see TODO in code). Operationally:
+
+- Prefer to keep backend config identical across ranks
+- If attach fails, immediately call detach (best-effort/idempotent), fix config, then retry attach
+
+---
+
+## 3. How to use (HTTP Admin API)
+
+The examples below assume your SGLang HTTP server is at `http://127.0.0.1:30000`.
+
+### 3.1 Query current storage backend status
+
+```bash
+curl -s http://127.0.0.1:30000/hicache/storage-backend
+```
+
+Example response:
+
+```json
+{
+  "hicache_storage_backend": "mooncake",
+  "hicache_storage_backend_extra_config": "{\"master_server_address\":\"127.0.0.1:50051\", ...}"
+}
+```
+
+### 3.2 Attach (enable) a storage backend
+```bash
+curl -s -X PUT http://127.0.0.1:30000/hicache/storage-backend \
+  -H 'Content-Type: application/json' \
+  -d '{
+    "hicache_storage_backend": "mooncake"
+  }'
+```
+
+```bash
+curl -s -X PUT http://127.0.0.1:30000/hicache/storage-backend \
+  -H 'Content-Type: application/json' \
+  -d '{
+    "hicache_storage_backend": "mooncake",
+    "hicache_storage_backend_extra_config_json": "{\"master_server_address\":\"127.0.0.1:50051\",\"protocol\":\"tcp\",\"global_segment_size\":\"4gb\",\"prefetch_threshold\":256}",
+    "hicache_storage_prefetch_policy": "timeout"
+  }'
+```
+
+Notes:
+
+- `hicache_storage_backend_extra_config_json` can include both:
+  - **Backend configuration** (e.g., Mooncake master/metadata/protocol, etc.)
+  - **Prefetch configuration** (`prefetch_threshold`, `prefetch_timeout_base`, `prefetch_timeout_per_ki_token`, `hicache_storage_pass_prefix_keys`)
+
+### 3.3 Detach (disable) the storage backend
+
+```bash
+curl -s -X DELETE http://127.0.0.1:30000/hicache/storage-backend
+```
+
+Notes:
+
+- Detach only makes SGLang **stop using** the L3 storage backend and stops prefetch/backup threads
+- It **does not automatically delete** data stored in Mooncake/HF3FS (or other remote backends)
+
+---
+
+## 4. Behavior and caveats
+
+- **No restart required**: attach/detach switches in-process at runtime
+- **Must be idle**: otherwise the request is rejected to avoid consistency issues
+- **Host KV layout constraints still apply**: for example, Mooncake still requires layouts like `page_first/page_first_direct/page_head`; if the server's HiCache host-memory layout does not satisfy the backend requirements, attach will fail with an error
+- **Observability**:
+  - After attach, `server_args.hicache_storage_backend*` is updated on both the tokenizer and scheduler sides
+  - If metrics are enabled, attach will create a storage metrics collector in `HiRadixCache` on demand

python/sglang/srt/entrypoints/http_server.py

@@ -93,6 +93,7 @@ from sglang.srt.environ import envs
 from sglang.srt.function_call.function_call_parser import FunctionCallParser
 from sglang.srt.managers.io_struct import (
     AbortReq,
+    AttachHiCacheStorageReqInput,
     CheckWeightsReqInput,
     CloseSessionReqInput,
     ConfigureLoggingReq,
@@ -693,6 +694,22 @@ async def flush_cache():
 
 @app.api_route("/clear_hicache_storage_backend", methods=["GET", "POST"])
 @auth_level(AuthLevel.ADMIN_OPTIONAL)
+async def clear_hicache_storage_backend_deprecated():
+    """Deprecated: use POST /hicache/storage-backend/clear."""
+    ret = await _global_state.tokenizer_manager.clear_hicache_storage()
+    return Response(
+        content=(
+            "Deprecated endpoint. Use POST /hicache/storage-backend/clear.\n"
+            "Hierarchical cache storage backend cleared.\n"
+        ),
+        status_code=200 if ret.success else HTTPStatus.BAD_REQUEST,
+    )
+
+
+# example usage:
+# curl -s -X POST http://127.0.0.1:30000/clear_hicache_storage_backend
+@app.api_route("/hicache/storage-backend/clear", methods=["POST"])
+@auth_level(AuthLevel.ADMIN_OPTIONAL)
 async def clear_hicache_storage_backend():
     """Clear the hierarchical cache storage backend."""
     ret = await _global_state.tokenizer_manager.clear_hicache_storage()
@@ -702,6 +719,89 @@ async def clear_hicache_storage_backend():
     )
 
 
+# example usage:
+# curl -s -X PUT http://127.0.0.1:30000/hicache/storage-backend \
+#  -H 'Content-Type: application/json' \
+#   -d '{
+#     "hicache_storage_backend": "file",
+#     "hicache_storage_backend_extra_config_json": "{}",
+#     "hicache_storage_prefetch_policy": "timeout",
+#     "hicache_write_policy": "write_through"
+#   }'
+@app.api_route("/hicache/storage-backend", methods=["PUT"])
+@auth_level(AuthLevel.ADMIN_OPTIONAL)
+async def attach_hicache_storage_backend(obj: AttachHiCacheStorageReqInput):
+    """Attach (enable) HiCache storage backend at runtime.
+
+    Only allowed when there are NO running / queued requests.
+    """
+    if not _global_state.tokenizer_manager.server_args.admin_api_key:
+        return _admin_api_key_missing_response()
+
+    ret = await _global_state.tokenizer_manager.attach_hicache_storage(
+        hicache_storage_backend=obj.hicache_storage_backend,
+        hicache_storage_backend_extra_config_json=obj.hicache_storage_backend_extra_config_json,
+        hicache_storage_prefetch_policy=obj.hicache_storage_prefetch_policy,
+        hicache_write_policy=obj.hicache_write_policy,
+    )
+    msg = getattr(ret, "message", "")
+    return Response(
+        content=(
+            (
+                "HiCache storage backend attached.\n"
+                if ret.success
+                else "Failed to attach HiCache storage backend.\n"
+            )
+            + (msg + "\n" if msg else "")
+        ),
+        status_code=200 if ret.success else HTTPStatus.BAD_REQUEST,
+    )
+
+
+# example usage:
+# curl -s -X DELETE http://127.0.0.1:30000/hicache/storage-backend
+@app.api_route("/hicache/storage-backend", methods=["DELETE"])
+@auth_level(AuthLevel.ADMIN_OPTIONAL)
+async def detach_hicache_storage_backend():
+    """Detach (disable) HiCache storage backend at runtime.
+
+    Only allowed when there are NO running / queued requests.
+    """
+    if not _global_state.tokenizer_manager.server_args.admin_api_key:
+        return _admin_api_key_missing_response()
+
+    ret = await _global_state.tokenizer_manager.detach_hicache_storage()
+    msg = getattr(ret, "message", "")
+    return Response(
+        content=(
+            (
+                "HiCache storage backend detached.\n"
+                if ret.success
+                else "Failed to detach HiCache storage backend.\n"
+            )
+            + (msg + "\n" if msg else "")
+        ),
+        status_code=200 if ret.success else HTTPStatus.BAD_REQUEST,
+    )
+
+
+# example usage:
+# curl -s http://127.0.0.1:30000/hicache/storage-backend
+@app.get("/hicache/storage-backend")
+@auth_level(AuthLevel.ADMIN_OPTIONAL)
+async def hicache_storage_backend_status():
+    """Get current HiCache storage backend status (tokenizer-side view)."""
+    if not _global_state.tokenizer_manager.server_args.admin_api_key:
+        return _admin_api_key_missing_response()
+
+    return {
+        "hicache_storage_backend": _global_state.tokenizer_manager.server_args.hicache_storage_backend,
+        "hicache_storage_backend_extra_config": _global_state.tokenizer_manager.server_args.hicache_storage_backend_extra_config,
+        "hicache_storage_prefetch_policy": _global_state.tokenizer_manager.server_args.hicache_storage_prefetch_policy,
+        "hicache_write_policy": _global_state.tokenizer_manager.server_args.hicache_write_policy,
+    }
+
+
 @app.api_route("/start_profile", methods=["GET", "POST"])
 @auth_level(AuthLevel.ADMIN_OPTIONAL)
 async def start_profile_async(obj: Optional[ProfileReqInput] = None):
@@ -1489,6 +1589,27 @@ def _create_error_response(e):
     )
 
 
+# FIXME: In theory we should configure ADMIN_FORCE for some entrypoints, but doing so
+# would currently cause all endpoints to go through add_api_key_middleware
+# (even when neither api-key nor admin-api-key is configured).
+#
+# For now, we simulate ADMIN_FORCE by explicitly checking the admin API key parameter.
+# Once the auth wiring is refactored so ADMIN_FORCE only affects the intended
+# admin endpoints, we should switch this logic to use ADMIN_FORCE directly.
+def _admin_api_key_missing_response(
+    status_code: HTTPStatus = HTTPStatus.BAD_REQUEST,
+) -> ORJSONResponse:
+    return ORJSONResponse(
+        content={
+            "error": (
+                "This endpoint requires admin API key, but this server was started "
+                "without one (admin-api-key). Restart with --admin-api-key to enable."
+            )
+        },
+        status_code=status_code,
+    )
+
+
 # Minimal 32x32 black PNG (base64, GLM4v requires at least 32x32 sized image)
 MINIMUM_PNG_PICTURE_BASE64 = "iVBORw0KGgoAAAANSUhEUgAAACAAAAAgCAYAAABzenr0AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAbUlEQVRYhe3VsQ2AMAxE0Y/lIgNQULD/OqyCMgCihCKSG4yRuKuiNH6JLsoEbMACOGBcua9HOR7Y6w6swBwMy0qLTpkeI77qdEBpBFAHBBDAGH8WrwJKI4AAegUCfAKgEgpQDvh3CR3oQCuav58qlAw73kKCSgAAAABJRU5ErkJggg=="
 

python/sglang/srt/managers/cache_controller.py

@@ -262,6 +262,7 @@ class HiCacheController:
         pp_rank: int = 0,
         pp_size: int = 1,
     ):
+        self.tp_group = tp_group
         self.mem_pool_device_allocator = token_to_kv_pool_allocator
         self.mem_pool_device = token_to_kv_pool_allocator.get_kvcache()
         self.mem_pool_host = mem_pool_host
@@ -269,69 +270,20 @@ class HiCacheController:
         self.page_size = page_size
         self.io_backend = io_backend
         self.enable_storage = False
+        self.storage_backend = None
+        self.storage_backend_type = None
         self.pp_rank = pp_rank
         self.pp_size = pp_size
 
-        if storage_backend is not None:
+        # Default storage page IO functions (may be overridden by attach).
-            self.storage_backend_type = storage_backend
-            from sglang.srt.mem_cache.hicache_storage import get_hash_str
-
-            self.get_hash_str = get_hash_str
-            self.storage_config = self._generate_storage_config(
-                model_name, storage_backend_extra_config
-            )
-            # for MLA models, only one rank needs to backup the KV cache
-            self.backup_skip = (
-                self.storage_config.is_mla_model
-                # todo: load balancing
-                and self.storage_config.tp_rank != 0
-            )
-
-            # Use storage backend factory for dynamic backend creation
-            from sglang.srt.mem_cache.storage import StorageBackendFactory
-
-            try:
-                self.storage_backend = StorageBackendFactory.create_backend(
-                    storage_backend, self.storage_config, self.mem_pool_host
-                )
-            except ValueError as e:
-                raise ValueError(f"Failed to create storage backend: {e}") from e
-
-            self.storage_backend.register_mem_pool_host(self.mem_pool_host)
-
-            self.enable_storage = True
-            # todo: threshold policy for prefetching
-            self.prefetch_threshold = max(prefetch_threshold, self.page_size)
-            self.prefetch_capacity_limit = int(
-                0.8 * (self.mem_pool_host.size - self.mem_pool_device.size)
-            )
-            # granularity of batch storage IO operations, in number of pages
-            self.storage_batch_size = 128
-            # tracking the number of tokens locked in prefetching, updated by the main scheduler thread
-            self.prefetch_tokens_occupied = 0
-
-            # create a new communication group for synchronizing storage operations across TP workers
-            self.tp_world_size = torch.distributed.get_world_size(group=tp_group)
-            if self.tp_world_size > 1:
-                from sglang.srt.distributed.parallel_state import (
-                    create_custom_parallel_group,
-                )
-
-                group_ranks = torch.distributed.get_process_group_ranks(tp_group)
-                self.prefetch_tp_group = create_custom_parallel_group(
-                    group_ranks=group_ranks, backend="gloo"
-                )
-
-            # Select the get and set functions
         self.page_get_func = self._generic_page_get
         self.page_set_func = self._generic_page_set
 
-            if (self.storage_backend_type in ["hf3fs", "mooncake", "eic"]) or (
+        # Dedicated stop event for storage background threads (prefetch/backup).
-                self.storage_backend_type == "dynamic"
+        # NOTE: Do NOT reuse `self.stop_event` here since it also guards core HiCache
-                and bool(self.storage_config.extra_config.get("interface_v1", 0))
+        # transfer buffers (CPU<->GPU). We want to allow runtime attach/detach of
-            ):
+        # storage without stopping the whole controller.
-                self.page_get_func = self._page_get_zero_copy
+        self.storage_stop_event = threading.Event()
-                self.page_set_func = self._page_set_zero_copy
 
         self.device = self.mem_pool_device.device
         self.layer_num = self.mem_pool_device.layer_num
@@ -360,7 +312,28 @@ class HiCacheController:
         self.write_stream = device_module.Stream()
         self.load_stream = device_module.Stream()
 
-        if self.enable_storage:
+        # If a storage backend is provided at startup, treat it as an implicit attach,
+        # so init/runtime share the same lifecycle semantics and code paths.
+        if storage_backend is not None:
+            try:
+                self.attach_storage_backend(
+                    storage_backend=storage_backend,
+                    prefetch_threshold=prefetch_threshold,
+                    model_name=model_name,
+                    storage_backend_extra_config=storage_backend_extra_config,
+                )
+            except ValueError as e:
+                # Preserve the historical error shape on init for unknown backends.
+                raise ValueError(f"Failed to create storage backend: {e}") from e
+
+    def _start_storage_threads(self):
+        """Start storage prefetch/backup threads and their queues.
+
+        This is used by runtime attach, and also by reset when storage is enabled.
+        """
+        assert self.enable_storage
+        assert not self.storage_stop_event.is_set()
+
         self.prefetch_thread = threading.Thread(
             target=self.prefetch_thread_func, daemon=True
         )
@@ -377,6 +350,222 @@ class HiCacheController:
         self.prefetch_thread.start()
         self.backup_thread.start()
 
+    def _stop_storage_threads(self):
+        """Stop storage prefetch/backup threads and drain internal queues.
+
+        Caller should ensure no in-flight requests.
+        """
+        # Always request stop. This is safe even when storage is already disabled,
+        # and makes detach truly idempotent (previous partial detach may have left
+        # threads alive).
+        # NOTE: do NOT clear stop_event unless threads have fully stopped; otherwise
+        # a still-alive thread may resume and touch released state.
+        self.storage_stop_event.set()
+
+        # Best-effort wakeups so threads exit promptly even if blocked on queues.
+        try:
+            if hasattr(self, "prefetch_queue"):
+                self.prefetch_queue.put_nowait(None)
+            if hasattr(self, "backup_queue"):
+                self.backup_queue.put_nowait(None)
+            if hasattr(self, "prefetch_buffer"):
+                self.prefetch_buffer.put_nowait(None)
+        except Exception:
+            pass
+
+        # Best-effort joins (threads are daemon, but join keeps state clean).
+        threads = []
+        if hasattr(self, "prefetch_thread"):
+            threads.append(self.prefetch_thread)
+        if hasattr(self, "backup_thread"):
+            threads.append(self.backup_thread)
+        if hasattr(self, "prefetch_io_aux_thread"):
+            threads.append(self.prefetch_io_aux_thread)
+
+        for t in threads:
+            try:
+                t.join(timeout=10)
+            except Exception:
+                pass
+
+        alive = [t for t in threads if getattr(t, "is_alive", lambda: False)()]
+        if alive:
+            logger.error(
+                "Failed to stop HiCache storage threads cleanly: %s",
+                [getattr(t, "name", repr(t)) for t in alive],
+            )
+            raise RuntimeError("Failed to stop HiCache storage threads cleanly.")
+
+    def attach_storage_backend(
+        self,
+        storage_backend: str,
+        prefetch_threshold: int = 256,
+        model_name: Optional[str] = None,
+        storage_backend_extra_config: Optional[dict] = None,
+    ):
+        """Attach (enable) storage backend at runtime.
+
+        Requirement: no in-flight requests. This call is expected to run on the scheduler
+        thread (control path), not concurrently with prefetch/backup.
+        """
+        if self.enable_storage:
+            raise RuntimeError("Storage backend already attached.")
+
+        # Defensive: a previous partial detach may have flipped `enable_storage` but
+        # left background threads alive. Attaching on top of them is unsafe.
+        try:
+            self._stop_storage_threads()
+        except Exception as e:
+            raise RuntimeError(
+                "Cannot attach storage backend: previous detach did not stop storage threads cleanly."
+            ) from e
+
+        # Rollback-safe init: if creation fails, keep controller state consistent
+        # for future attach attempts.
+        self.storage_backend_type = storage_backend
+        from sglang.srt.mem_cache.hicache_storage import get_hash_str
+
+        self.get_hash_str = get_hash_str
+        self.storage_config = self._generate_storage_config(
+            model_name, storage_backend_extra_config
+        )
+        # for MLA models, only one rank needs to backup the KV cache
+        self.backup_skip = (
+            self.storage_config.is_mla_model
+            # todo: load balancing
+            and self.storage_config.tp_rank != 0
+        )
+
+        # Use storage backend factory for dynamic backend creation
+        from sglang.srt.mem_cache.storage import StorageBackendFactory
+
+        try:
+            self.storage_backend = StorageBackendFactory.create_backend(
+                storage_backend, self.storage_config, self.mem_pool_host
+            )
+            self.storage_backend.register_mem_pool_host(self.mem_pool_host)
+
+            self.enable_storage = True
+            # todo: threshold policy for prefetching
+            self.prefetch_threshold = max(prefetch_threshold, self.page_size)
+            self.prefetch_capacity_limit = max(
+                0, int(0.8 * (self.mem_pool_host.size - self.mem_pool_device.size))
+            )
+            # granularity of batch storage IO operations, in number of pages
+            self.storage_batch_size = 128
+            # tracking the number of tokens locked in prefetching, updated by the main scheduler thread
+            self.prefetch_tokens_occupied = 0
+
+            # create a new communication group for synchronizing storage operations across TP workers
+            self.tp_world_size = torch.distributed.get_world_size(group=self.tp_group)
+            if self.tp_world_size > 1:
+                from sglang.srt.distributed.parallel_state import (
+                    create_custom_parallel_group,
+                )
+
+                group_ranks = torch.distributed.get_process_group_ranks(self.tp_group)
+                self.prefetch_tp_group = create_custom_parallel_group(
+                    group_ranks=group_ranks, backend="gloo"
+                )
+
+            # Select the get and set functions
+            self.page_get_func = self._generic_page_get
+            self.page_set_func = self._generic_page_set
+
+            if (self.storage_backend_type in ["hf3fs", "mooncake", "eic"]) or (
+                self.storage_backend_type == "dynamic"
+                and bool(self.storage_config.extra_config.get("interface_v1", 0))
+            ):
+                self.page_get_func = self._page_get_zero_copy
+                self.page_set_func = self._page_set_zero_copy
+
+            # Ensure stop_event is clear before starting threads.
+            self.storage_stop_event.clear()
+            self._start_storage_threads()
+        except Exception:
+            # Best-effort cleanup for partial init.
+            try:
+                self._stop_storage_threads()
+            except Exception:
+                pass
+            try:
+                if hasattr(self, "prefetch_tp_group"):
+                    try:
+                        torch.distributed.destroy_process_group(self.prefetch_tp_group)
+                    except Exception:
+                        pass
+                    self.prefetch_tp_group = None
+            except Exception:
+                pass
+            try:
+                if (
+                    hasattr(self, "storage_backend")
+                    and self.storage_backend is not None
+                ):
+                    if hasattr(self.storage_backend, "close"):
+                        self.storage_backend.close()
+            except Exception:
+                pass
+            self.storage_backend = None
+            self.storage_backend_type = None
+            self.enable_storage = False
+            self.page_get_func = self._generic_page_get
+            self.page_set_func = self._generic_page_set
+            raise
+
+    def detach_storage_backend(self):
+        """Detach (disable) storage backend at runtime.
+
+        Requirement: no in-flight requests. This will stop storage threads and release
+        the backend instance (best-effort close).
+        """
+        # Idempotent cleanup: even if `enable_storage` is already False,
+        # we may still have leftover resources (threads/backend/process group) from a
+        # previous partial detach. We attempt cleanup whenever possible.
+        try:
+            self._stop_storage_threads()
+        except Exception as e:
+            # Do not proceed tearing down backend/process group if threads are not
+            # fully stopped; otherwise still-alive threads may touch released state.
+            # Caller can retry detach.
+            logger.exception("Stop storage threads failed: %s", e)
+            # IMPORTANT: Do not silently succeed. Upper layers rely on exceptions here
+            # to avoid flipping `enable_storage` flags while threads are still alive.
+            raise RuntimeError("Stop storage threads failed; detach aborted.") from e
+
+        # Best-effort destroy process group created for storage ops.
+        try:
+            if (
+                hasattr(self, "prefetch_tp_group")
+                and self.prefetch_tp_group is not None
+            ):
+                try:
+                    torch.distributed.destroy_process_group(self.prefetch_tp_group)
+                except Exception:
+                    pass
+                self.prefetch_tp_group = None
+        except Exception:
+            pass
+
+        # Best-effort close (some backends rely on GC/destructor).
+        try:
+            if (
+                hasattr(self, "storage_backend")
+                and self.storage_backend is not None
+                and hasattr(self.storage_backend, "close")
+            ):
+                self.storage_backend.close()
+        except Exception:
+            logger.exception("Failed to close storage backend cleanly.")
+
+        self.storage_backend = None
+        self.storage_backend_type = None
+        self.enable_storage = False
+        self.page_get_func = self._generic_page_get
+        self.page_set_func = self._generic_page_set
+        # Now it's safe to clear the stop event for future re-attach.
+        self.storage_stop_event.clear()
+
     def _generate_storage_config(
         self,
         model_name: Optional[str] = None,
@@ -408,6 +597,7 @@ class HiCacheController:
 
     def reset(self):
         self.stop_event.set()
+        self.storage_stop_event.set()
 
         self.write_queue.clear()
         self.load_queue.clear()
@@ -424,6 +614,7 @@ class HiCacheController:
             self.ack_backup_queue.queue.clear()
 
         self.stop_event.clear()
+        self.storage_stop_event.clear()
 
         if self.enable_storage:
             self.prefetch_thread = threading.Thread(
@@ -661,9 +852,11 @@ class HiCacheController:
         """
         Auxiliary function conducting IO operations for prefetching.
         """
-        while not self.stop_event.is_set():
+        while not self.storage_stop_event.is_set():
             try:
                 operation = self.prefetch_buffer.get(block=True, timeout=1)
+                if operation is None:
+                    continue
                 self._page_transfer(operation)
                 # operation terminated by controller, release pre-allocated memory
                 self.append_host_mem_release(
@@ -719,9 +912,11 @@ class HiCacheController:
         Manage prefetching operations from storage backend to host memory.
         """
         self.prefetch_buffer = Queue()
-        aux_thread = threading.Thread(target=self.prefetch_io_aux_func, daemon=True)
+        self.prefetch_io_aux_thread = threading.Thread(
-        aux_thread.start()
+            target=self.prefetch_io_aux_func, daemon=True
-        while (not self.stop_event.is_set()) or not self.prefetch_queue.empty():
+        )
+        self.prefetch_io_aux_thread.start()
+        while (not self.storage_stop_event.is_set()) or not self.prefetch_queue.empty():
             try:
                 operation = self.prefetch_queue.get(block=True, timeout=1)
                 if operation is None:
@@ -818,7 +1013,7 @@ class HiCacheController:
         """
         Manage backup operations from host memory to storage backend.
         """
-        while not self.stop_event.is_set():
+        while not self.storage_stop_event.is_set():
             try:
                 operation = self.backup_queue.get(block=True, timeout=1)
                 if operation is None:

python/sglang/srt/managers/io_struct.py

@@ -1158,6 +1158,60 @@ class FlushCacheReqOutput(BaseReq):
     success: bool
 
 
+@dataclass
+class AttachHiCacheStorageReqInput(BaseReq):
+    """Dynamically attach (enable) HiCache storage backend at runtime.
+
+    Note: `hicache_storage_backend_extra_config_json` is a JSON string. It may contain both:
+    - backend-specific configs (e.g., mooncake master address)
+    - prefetch-related knobs (prefetch_threshold, prefetch_timeout_*, hicache_storage_pass_prefix_keys)
+    """
+
+    hicache_storage_backend: str
+    hicache_storage_backend_extra_config_json: Optional[str] = None
+    hicache_storage_prefetch_policy: Optional[str] = None
+    hicache_write_policy: Optional[str] = None
+
+    def __post_init__(self):
+        if self.hicache_storage_prefetch_policy is None:
+            pass
+        else:
+            allowed = ["best_effort", "wait_complete", "timeout"]
+            if self.hicache_storage_prefetch_policy not in allowed:
+                raise ValueError(
+                    f"Invalid hicache_storage_prefetch_policy: {self.hicache_storage_prefetch_policy!r}. "
+                    f"Expected one of {allowed}."
+                )
+
+        if self.hicache_write_policy is None:
+            return
+        allowed = ["write_back", "write_through", "write_through_selective"]
+        if self.hicache_write_policy not in allowed:
+            raise ValueError(
+                f"Invalid hicache_write_policy: {self.hicache_write_policy!r}. "
+                f"Expected one of {allowed}."
+            )
+
+
+@dataclass
+class AttachHiCacheStorageReqOutput(BaseReq):
+    success: bool
+    message: str = ""
+
+
+@dataclass
+class DetachHiCacheStorageReqInput(BaseReq):
+    """Dynamically detach (disable) HiCache storage backend at runtime."""
+
+    pass
+
+
+@dataclass
+class DetachHiCacheStorageReqOutput(BaseReq):
+    success: bool
+    message: str = ""
+
+
 @dataclass
 class PauseGenerationReqInput(BaseReq):
     """

python/sglang/srt/managers/scheduler.py

@@ -71,6 +71,8 @@ from sglang.srt.lora.lora_overlap_loader import LoRAOverlapLoader
 from sglang.srt.managers.io_struct import (
     AbortReq,
     ActiveRanksOutput,
+    AttachHiCacheStorageReqInput,
+    AttachHiCacheStorageReqOutput,
     BaseBatchReq,
     BaseReq,
     BatchTokenizedEmbeddingReqInput,
@@ -81,6 +83,8 @@ from sglang.srt.managers.io_struct import (
     CloseSessionReqInput,
     ContinueGenerationReqInput,
     DestroyWeightsUpdateGroupReqInput,
+    DetachHiCacheStorageReqInput,
+    DetachHiCacheStorageReqOutput,
     ExpertDistributionReq,
     ExpertDistributionReqOutput,
     ExpertDistributionReqType,
@@ -1008,6 +1012,8 @@ class Scheduler(
                 (BatchTokenizedEmbeddingReqInput, self.handle_batch_embedding_request),
                 (FlushCacheReqInput, self.flush_cache_wrapped),
                 (ClearHiCacheReqInput, self.clear_hicache_storage_wrapped),
+                (AttachHiCacheStorageReqInput, self.attach_hicache_storage_wrapped),
+                (DetachHiCacheStorageReqInput, self.detach_hicache_storage_wrapped),
                 (AbortReq, self.abort_request),
                 (OpenSessionReqInput, self.open_session),
                 (CloseSessionReqInput, self.close_session),
@@ -2428,6 +2434,118 @@ class Scheduler(
             if_success = False
         return ClearHiCacheReqOutput(success=if_success)
 
+    def _is_idle_for_hicache_storage_op(self) -> bool:
+        """Stricter idle check for storage attach/detach.
+
+        We require:
+        - no running batches (including overlap/pp/disagg paths) via `_is_no_request()`
+        - no queued requests in scheduler queues (waiting/grammar/disagg queues)
+        """
+        if not self._is_no_request():
+            return False
+        if len(self.waiting_queue) != 0:
+            return False
+        if len(self.grammar_manager.grammar_queue) != 0:
+            return False
+        return True
+
+    def attach_hicache_storage_wrapped(
+        self, recv_req: AttachHiCacheStorageReqInput
+    ) -> AttachHiCacheStorageReqOutput:
+        if not self.enable_hierarchical_cache:
+            return AttachHiCacheStorageReqOutput(
+                success=False, message="Hierarchical cache is not enabled."
+            )
+
+        if not self._is_idle_for_hicache_storage_op():
+            return AttachHiCacheStorageReqOutput(
+                success=False,
+                message=(
+                    "Reject attach: scheduler is not idle. "
+                    f"#queue-req={len(self.waiting_queue)} "
+                    f"#running-req={len(self.running_batch.reqs)}"
+                ),
+            )
+
+        if not hasattr(self.tree_cache, "attach_storage_backend"):
+            return AttachHiCacheStorageReqOutput(
+                success=False,
+                message="Current tree_cache implementation does not support dynamic attach.",
+            )
+
+        try:
+            ok, msg = self.tree_cache.attach_storage_backend(
+                storage_backend=recv_req.hicache_storage_backend,
+                storage_backend_extra_config_json=recv_req.hicache_storage_backend_extra_config_json,
+                served_model_name=self.server_args.served_model_name,
+                hicache_storage_prefetch_policy=recv_req.hicache_storage_prefetch_policy,
+                hicache_write_policy=recv_req.hicache_write_policy,
+            )
+        except Exception as e:
+            logger.exception("Attach HiCache storage backend failed with exception.")
+            return AttachHiCacheStorageReqOutput(success=False, message=str(e))
+        if ok:
+            self.enable_hicache_storage = True
+            self.server_args.hicache_storage_backend = recv_req.hicache_storage_backend
+            if recv_req.hicache_storage_backend_extra_config_json is not None:
+                self.server_args.hicache_storage_backend_extra_config = (
+                    recv_req.hicache_storage_backend_extra_config_json
+                )
+            if recv_req.hicache_storage_prefetch_policy is not None:
+                self.server_args.hicache_storage_prefetch_policy = (
+                    recv_req.hicache_storage_prefetch_policy
+                )
+            if recv_req.hicache_write_policy is not None:
+                self.server_args.hicache_write_policy = recv_req.hicache_write_policy
+            logger.info(
+                f"Attached HiCache storage backend: {recv_req.hicache_storage_backend}"
+            )
+        return AttachHiCacheStorageReqOutput(success=ok, message=msg)
+
+    def detach_hicache_storage_wrapped(
+        self, recv_req: DetachHiCacheStorageReqInput
+    ) -> DetachHiCacheStorageReqOutput:
+        if not self.enable_hierarchical_cache:
+            return DetachHiCacheStorageReqOutput(
+                success=False, message="Hierarchical cache is not enabled."
+            )
+
+        if not self._is_idle_for_hicache_storage_op():
+            return DetachHiCacheStorageReqOutput(
+                success=False,
+                message=(
+                    "Reject detach: scheduler is not idle. "
+                    f"#queue-req={len(self.waiting_queue)} "
+                    f"#running-req={len(self.running_batch.reqs)}"
+                ),
+            )
+
+        if not hasattr(self.tree_cache, "detach_storage_backend"):
+            return DetachHiCacheStorageReqOutput(
+                success=False,
+                message="Current tree_cache implementation does not support dynamic detach.",
+            )
+
+        # Idempotent detach: even if scheduler thinks storage is disabled, we still
+        # attempt best-effort cleanup in tree_cache (it may have leftover state).
+        try:
+            ok, msg = self.tree_cache.detach_storage_backend()
+        except Exception as e:
+            logger.exception("Detach HiCache storage backend failed with exception.")
+            return DetachHiCacheStorageReqOutput(success=False, message=str(e))
+
+        if ok or (not self.enable_hicache_storage):
+            # Treat "already disabled / nothing to do" as success for idempotence.
+            self.enable_hicache_storage = False
+            self.server_args.hicache_storage_backend = None
+            self.server_args.hicache_storage_backend_extra_config = None
+            logger.info("Detached HiCache storage backend.")
+            return DetachHiCacheStorageReqOutput(
+                success=True, message=msg or "HiCache storage backend is detached."
+            )
+
+        return DetachHiCacheStorageReqOutput(success=False, message=msg)
+
     def _is_no_request(self):
         no_request = (
             self.running_batch.is_empty()

python/sglang/srt/managers/tokenizer_communicator_mixin.py

@@ -23,6 +23,8 @@ import fastapi
 import zmq
 
 from sglang.srt.managers.io_struct import (
+    AttachHiCacheStorageReqInput,
+    AttachHiCacheStorageReqOutput,
     CheckWeightsReqInput,
     CheckWeightsReqOutput,
     ClearHiCacheReqInput,
@@ -30,6 +32,8 @@ from sglang.srt.managers.io_struct import (
     CloseSessionReqInput,
     DestroyWeightsUpdateGroupReqInput,
     DestroyWeightsUpdateGroupReqOutput,
+    DetachHiCacheStorageReqInput,
+    DetachHiCacheStorageReqOutput,
     ExpertDistributionReq,
     ExpertDistributionReqOutput,
     ExpertDistributionReqType,
@@ -202,6 +206,12 @@ class TokenizerCommunicatorMixin:
         self.clear_hicache_storage_communicator = _Communicator(
             self.send_to_scheduler, server_args.dp_size
         )
+        self.attach_hicache_storage_communicator = _Communicator(
+            self.send_to_scheduler, server_args.dp_size
+        )
+        self.detach_hicache_storage_communicator = _Communicator(
+            self.send_to_scheduler, server_args.dp_size
+        )
         self.profile_communicator = _Communicator(
             self.send_to_scheduler, server_args.dp_size
         )
@@ -281,6 +291,14 @@ class TokenizerCommunicatorMixin:
                     ClearHiCacheReqOutput,
                     self.clear_hicache_storage_communicator.handle_recv,
                 ),
+                (
+                    AttachHiCacheStorageReqOutput,
+                    self.attach_hicache_storage_communicator.handle_recv,
+                ),
+                (
+                    DetachHiCacheStorageReqOutput,
+                    self.detach_hicache_storage_communicator.handle_recv,
+                ),
                 (
                     FlushCacheReqOutput,
                     self.flush_cache_communicator.handle_recv,
@@ -326,6 +344,57 @@ class TokenizerCommunicatorMixin:
             0
         ]
 
+    async def attach_hicache_storage(
+        self: TokenizerManager,
+        hicache_storage_backend: str,
+        hicache_storage_backend_extra_config_json: Optional[str] = None,
+        hicache_storage_prefetch_policy: Optional[str] = None,
+        hicache_write_policy: Optional[str] = None,
+    ) -> AttachHiCacheStorageReqOutput:
+        """Attach (enable) HiCache storage backend at runtime."""
+        results = await self.attach_hicache_storage_communicator(
+            AttachHiCacheStorageReqInput(
+                hicache_storage_backend=hicache_storage_backend,
+                hicache_storage_backend_extra_config_json=hicache_storage_backend_extra_config_json,
+                hicache_storage_prefetch_policy=hicache_storage_prefetch_policy,
+                hicache_write_policy=hicache_write_policy,
+            )
+        )
+
+        all_success, all_message = _Communicator.merge_results(results)
+        out = AttachHiCacheStorageReqOutput(success=all_success, message=all_message)
+        # TODO: partial rollback if failed
+        if all_success:
+            # Keep tokenizer side server_info consistent with scheduler side.
+            self.server_args.hicache_storage_backend = hicache_storage_backend
+            if hicache_storage_backend_extra_config_json is not None:
+                self.server_args.hicache_storage_backend_extra_config = (
+                    hicache_storage_backend_extra_config_json
+                )
+            if hicache_storage_prefetch_policy is not None:
+                self.server_args.hicache_storage_prefetch_policy = (
+                    hicache_storage_prefetch_policy
+                )
+            if hicache_write_policy is not None:
+                self.server_args.hicache_write_policy = hicache_write_policy
+        return out
+
+    async def detach_hicache_storage(
+        self: TokenizerManager,
+    ) -> DetachHiCacheStorageReqOutput:
+        """Detach (disable) HiCache storage backend at runtime."""
+        results = await self.detach_hicache_storage_communicator(
+            DetachHiCacheStorageReqInput()
+        )
+
+        all_success, all_message = _Communicator.merge_results(results)
+        out = DetachHiCacheStorageReqOutput(success=all_success, message=all_message)
+        # TODO: partial rollback if failed
+        if all_success:
+            self.server_args.hicache_storage_backend = None
+            self.server_args.hicache_storage_backend_extra_config = None
+        return out
+
     async def start_profile(
         self: TokenizerManager,
         output_dir: Optional[str] = None,

python/sglang/srt/mem_cache/hiradix_cache.py

@@ -1,11 +1,13 @@
 from __future__ import annotations
 
+import atexit
 import heapq
 import json
 import logging
 import os
 import threading
 import time
+from queue import Empty
 from typing import TYPE_CHECKING, List, Optional
 
 import torch
@@ -44,6 +46,7 @@ logger = logging.getLogger(__name__)
 class HiRadixCache(RadixCache):
 
     def __init__(self, params: CacheInitParams, server_args: ServerArgs):
+        self._enable_metrics_flag = params.enable_metrics
         if server_args.hicache_io_backend == "direct":
             # FIXME: move this logic into server_args parsing
             if server_args.hicache_mem_layout == "page_first":
@@ -95,12 +98,6 @@ class HiRadixCache(RadixCache):
         ) = self._parse_storage_backend_extra_config(
             server_args.hicache_storage_backend_extra_config
         )
-        self.prefetch_threshold = prefetch_threshold
-        self.prefetch_timeout_base = prefetch_timeout_base
-        self.prefetch_timeout_per_page = (
-            self.page_size / 1024 * prefetch_timeout_per_ki_token
-        )
-        self.hicache_storage_pass_prefix_keys = hicache_storage_pass_prefix_keys
         # TODO: support more timeout check functions
         self.is_prefetch_timeout = self._prefetch_timeout_check_linear_func
         self.prefetch_stop_policy = server_args.hicache_storage_prefetch_policy
@@ -115,22 +112,21 @@ class HiRadixCache(RadixCache):
             write_policy=server_args.hicache_write_policy,
             io_backend=server_args.hicache_io_backend,
             storage_backend=server_args.hicache_storage_backend,
-            prefetch_threshold=self.prefetch_threshold,
+            prefetch_threshold=prefetch_threshold,
             model_name=server_args.served_model_name,
             storage_backend_extra_config=extra_config,
             pp_rank=self.pp_rank,
             pp_size=self.pp_size,
         )
-        if self.enable_storage_metrics:
+        self._apply_storage_runtime_config(
-            # TODO: support pp
+            storage_backend=server_args.hicache_storage_backend,
-            labels = {
+            prefetch_threshold=prefetch_threshold,
-                "storage_backend": server_args.hicache_storage_backend,
+            prefetch_timeout_base=prefetch_timeout_base,
-                "tp_rank": self.cache_controller.tp_rank,
+            prefetch_timeout_per_ki_token=prefetch_timeout_per_ki_token,
-                "dp_rank": self.cache_controller.dp_rank,
+            hicache_storage_pass_prefix_keys=hicache_storage_pass_prefix_keys,
-                "pp_rank": self.cache_controller.pp_rank,
+            enable_storage=self.enable_storage,
-                "pp_size": self.cache_controller.pp_size,
+            enable_storage_metrics=self.enable_storage_metrics,
-            }
+        )
-            self.storage_metrics_collector = StorageMetricsCollector(labels=labels)
 
         # record the nodes with ongoing write through
         self.ongoing_write_through = {}
@@ -145,8 +141,333 @@ class HiRadixCache(RadixCache):
         )
         self.load_back_threshold = 10
 
+        # Detach storage backend automatically on process shutdown
+        atexit.register(self.shutdown)
+
         super().__init__(params=params)
 
+    def shutdown(self):
+        """Best-effort auto-detach of storage backend on process shutdown.
+
+        This keeps startup and runtime behavior consistent: if a backend was attached
+        (either via CLI args or via admin API), we attempt to detach it on exit.
+        """
+        try:
+            if self.enable_storage:
+                self.detach_storage_backend()
+        except Exception:
+            logger.exception("Failed to detach storage backend on process shutdown.")
+
+    def _apply_storage_runtime_config(
+        self,
+        *,
+        storage_backend: Optional[str],
+        prefetch_threshold: int,
+        prefetch_timeout_base: float,
+        prefetch_timeout_per_ki_token: float,
+        hicache_storage_pass_prefix_keys: bool,
+        enable_storage: bool,
+        enable_storage_metrics: bool,
+    ) -> None:
+        prefetch_timeout_per_page = (
+            self.page_size / 1024 * prefetch_timeout_per_ki_token
+        )
+
+        storage_metrics_collector = None
+        if enable_storage_metrics:
+            labels = {
+                "storage_backend": storage_backend,
+                "tp_rank": self.cache_controller.tp_rank,
+                "dp_rank": self.cache_controller.dp_rank,
+                "pp_rank": self.cache_controller.pp_rank,
+                "pp_size": self.cache_controller.pp_size,
+            }
+            storage_metrics_collector = StorageMetricsCollector(labels=labels)
+
+        self.enable_storage = enable_storage
+        self.prefetch_threshold = prefetch_threshold
+        self.prefetch_timeout_base = prefetch_timeout_base
+        self.prefetch_timeout_per_page = prefetch_timeout_per_page
+        self.hicache_storage_pass_prefix_keys = hicache_storage_pass_prefix_keys
+        self.enable_storage_metrics = enable_storage_metrics
+        if self.enable_storage_metrics:
+            self.storage_metrics_collector = storage_metrics_collector
+        else:
+            self.storage_metrics_collector = None
+
+    def attach_storage_backend(
+        self,
+        storage_backend: str,
+        storage_backend_extra_config_json: Optional[str] = None,
+        served_model_name: Optional[str] = None,
+        hicache_storage_prefetch_policy: Optional[str] = None,
+        hicache_write_policy: Optional[str] = None,
+    ) -> tuple[bool, str]:
+        """Attach (enable) storage backend at runtime.
+
+        This will start storage threads inside `HiCacheController` and enable
+        prefetch/backup paths. Caller must ensure there are no running/queued
+        requests to avoid races.
+        """
+        # Validate inputs first (no side effects).
+        if hicache_storage_prefetch_policy is not None:
+            allowed = ["best_effort", "wait_complete", "timeout"]
+            if hicache_storage_prefetch_policy not in allowed:
+                return (
+                    False,
+                    f"Invalid hicache_storage_prefetch_policy: {hicache_storage_prefetch_policy!r}. "
+                    f"Expected one of {allowed}.",
+                )
+
+        if hicache_write_policy is not None:
+            allowed = ["write_back", "write_through", "write_through_selective"]
+            if hicache_write_policy not in allowed:
+                return (
+                    False,
+                    f"Invalid hicache_write_policy: {hicache_write_policy!r}. "
+                    f"Expected one of {allowed}.",
+                )
+
+        # If already enabled:
+        # - backend unchanged: treat as success, update policies only.
+        # - backend changed: treat as failure, do NOT update policies.
+        if self.enable_storage:
+            current_backend = self.cache_controller.storage_backend_type
+
+            if current_backend == storage_backend:
+                if hicache_storage_prefetch_policy is not None:
+                    self.prefetch_stop_policy = hicache_storage_prefetch_policy
+                    logger.info(
+                        f"Set hicache_storage_prefetch_policy to {hicache_storage_prefetch_policy}"
+                    )
+                if hicache_write_policy is not None:
+                    self.cache_controller.write_policy = hicache_write_policy
+                    self.write_through_threshold = (
+                        1 if hicache_write_policy == "write_through" else 2
+                    )
+                    logger.info(f"Set hicache_write_policy to {hicache_write_policy}")
+                return (
+                    True,
+                    "HiCache storage backend already enabled with same backend; policies updated.",
+                )
+
+            return (
+                False,
+                f"HiCache storage backend is already enabled with backend '{current_backend}'. "
+                f"Cannot attach different backend '{storage_backend}'. Detach first.",
+            )
+
+        # Not enabled: update policies before controller attach so storage threads observe new values.
+        if hicache_storage_prefetch_policy is not None:
+            self.prefetch_stop_policy = hicache_storage_prefetch_policy
+            logger.info(
+                f"Set hicache_storage_prefetch_policy to {hicache_storage_prefetch_policy}"
+            )
+
+        if hicache_write_policy is not None:
+            self.cache_controller.write_policy = hicache_write_policy
+            self.write_through_threshold = (
+                1 if hicache_write_policy == "write_through" else 2
+            )
+            logger.info(f"Set hicache_write_policy to {hicache_write_policy}")
+
+        logger.info(f"Attaching HiCache storage backend: {storage_backend}")
+        try:
+            (
+                extra_config,
+                prefetch_threshold,
+                prefetch_timeout_base,
+                prefetch_timeout_per_ki_token,
+                hicache_storage_pass_prefix_keys,
+            ) = self._parse_storage_backend_extra_config(
+                storage_backend_extra_config_json
+            )
+        except Exception as e:
+            logger.exception(f"Failed to parse storage_backend_extra_config_json: {e}")
+            return (
+                False,
+                f"Failed to parse storage_backend_extra_config_json '{storage_backend_extra_config_json}': {e}",
+            )
+
+        try:
+            self.cache_controller.attach_storage_backend(
+                storage_backend=storage_backend,
+                prefetch_threshold=prefetch_threshold,
+                model_name=served_model_name,
+                storage_backend_extra_config=extra_config,
+            )
+        except Exception as e:
+            logger.exception(
+                f"Failed to attach storage backend '{storage_backend}': {e}"
+            )
+            return False, f"Failed to attach storage backend '{storage_backend}': {e}"
+
+        self._apply_storage_runtime_config(
+            storage_backend=storage_backend,
+            prefetch_threshold=prefetch_threshold,
+            prefetch_timeout_base=prefetch_timeout_base,
+            prefetch_timeout_per_ki_token=prefetch_timeout_per_ki_token,
+            hicache_storage_pass_prefix_keys=hicache_storage_pass_prefix_keys,
+            enable_storage=True,
+            enable_storage_metrics=self._enable_metrics_flag,
+        )
+        return True, "Attached HiCache storage backend successfully."
+
+    def detach_storage_backend(self) -> tuple[bool, str]:
+        """Detach (disable) storage backend at runtime.
+
+        Caller must ensure there are no running/queued requests to avoid races.
+        """
+        try:
+            # Drain any pending control queues before tearing down storage threads/backend.
+            # IMPORTANT: this must happen before we clear `ongoing_*`, otherwise acks/releases
+            # cannot be matched to nodes and may leak host pages / locks.
+            self._drain_storage_control_queues_local()
+            # Idempotent detach: always ask controller to best-effort cleanup, even if
+            # `self.enable_storage` is already False (may be leftover state from a
+            # previous partial detach).
+            self.cache_controller.detach_storage_backend()
+        except Exception as e:
+            logger.exception("Failed to detach storage backend.")
+            # Do NOT crash the server for admin operations. Return failure with detail.
+            return False, f"Failed to detach HiCache storage backend: {e}"
+
+        # Best-effort cleanup of any leftover bookkeeping.
+        self._drain_storage_control_queues_local()
+        # After controller threads are fully stopped, it's safe to force-release any
+        # leftover pending ops (e.g., async prefetch/backup that didn't get a revoke/ack).
+        self._force_release_pending_storage_ops()
+
+        self.enable_storage = False
+        self.enable_storage_metrics = False
+        if hasattr(self, "storage_metrics_collector"):
+            self.storage_metrics_collector = None
+        return True, "Detached HiCache storage backend successfully."
+
+    def _force_release_pending_storage_ops(self):
+        """Force release any leftover pending prefetch/backup bookkeeping.
+
+        This is a safety net for detach/shutdown paths. It assumes storage threads
+        have been stopped already (via controller.detach), so no concurrent access
+        to these structures should happen.
+        """
+        cc = self.cache_controller
+
+        # Force release leftover prefetch ops: free pre-allocated host pages and
+        # drop the host protection on the matched prefix node.
+        try:
+            for req_id, info in list(self.ongoing_prefetch.items()):
+                try:
+                    last_host_node, token_ids, host_indices, _operation = info
+                except Exception:
+                    # Unexpected shape; just drop it.
+                    self.ongoing_prefetch.pop(req_id, None)
+                    continue
+
+                try:
+                    if host_indices is not None:
+                        cc.mem_pool_host.free(host_indices)
+                except Exception:
+                    logger.exception(
+                        "Failed to free host indices for prefetch %s", req_id
+                    )
+
+                try:
+                    last_host_node.release_host()
+                except Exception:
+                    logger.exception(
+                        "Failed to release host protection for prefetch %s", req_id
+                    )
+
+                try:
+                    cc.prefetch_tokens_occupied -= len(token_ids)
+                    if cc.prefetch_tokens_occupied < 0:
+                        cc.prefetch_tokens_occupied = 0
+                except Exception:
+                    pass
+
+                self.ongoing_prefetch.pop(req_id, None)
+        except Exception:
+            logger.exception("Force release pending prefetch ops failed.")
+
+        # Force release leftover backup ops: drop host protection on nodes.
+        try:
+            for ack_id, node in list(self.ongoing_backup.items()):
+                try:
+                    node.release_host()
+                except Exception:
+                    logger.exception(
+                        "Failed to release host protection for backup op %s", ack_id
+                    )
+                self.ongoing_backup.pop(ack_id, None)
+        except Exception:
+            logger.exception("Force release pending backup ops failed.")
+
+    def _drain_storage_control_queues_local(self):
+        """Drain storage control queues without TP synchronization.
+
+        This is intended for shutdown/detach paths where we want to make best-effort
+        cleanup even if queue sizes temporarily differ across ranks.
+        """
+        self._drain_storage_control_queues_impl(
+            n_revoke=None,
+            n_backup=None,
+            n_release=None,
+            log_metrics=False,
+        )
+
+    def _drain_storage_control_queues_impl(
+        self,
+        n_revoke: Optional[int],
+        n_backup: Optional[int],
+        n_release: Optional[int],
+        log_metrics: bool,
+    ):
+        cc = self.cache_controller
+
+        def _drain_queue(q, limit: Optional[int]):
+            drained = 0
+            while limit is None or drained < limit:
+                try:
+                    item = q.get_nowait()
+                except Empty:
+                    break
+                drained += 1
+                yield item
+
+        def _drain_revoke():
+            for req_id in _drain_queue(cc.prefetch_revoke_queue, n_revoke):
+                info = self.ongoing_prefetch.pop(req_id, None)
+                if info is not None:
+                    last_host_node, token_ids, _, _ = info
+                    last_host_node.release_host()
+                    cc.prefetch_tokens_occupied -= len(token_ids)
+                    if cc.prefetch_tokens_occupied < 0:
+                        cc.prefetch_tokens_occupied = 0
+
+        def _drain_backup():
+            for operation in _drain_queue(cc.ack_backup_queue, n_backup):
+                ack_id = operation.id
+                entry = self.ongoing_backup.pop(ack_id, None)
+                if entry is not None:
+                    entry.release_host()
+                if log_metrics and self.enable_storage_metrics:
+                    self.storage_metrics_collector.log_backuped_tokens(
+                        operation.completed_tokens
+                    )
+
+        def _drain_release():
+            host_indices_list = []
+            for host_indices in _drain_queue(cc.host_mem_release_queue, n_release):
+                host_indices_list.append(host_indices)
+            if host_indices_list:
+                host_indices = torch.cat(host_indices_list, dim=0)
+                cc.mem_pool_host.free(host_indices)
+
+        _drain_revoke()
+        _drain_backup()
+        _drain_release()
+
     def _parse_storage_backend_extra_config(
         self, storage_backend_extra_config: Optional[str]
     ):
@@ -210,6 +531,11 @@ class HiRadixCache(RadixCache):
             raise ValueError(
                 f"prefetch_timeout_per_ki_token must be number, got {type(prefetch_timeout_per_ki_token).__name__}"
             )
+        if not isinstance(hicache_storage_pass_prefix_keys, bool):
+            raise ValueError(
+                "hicache_storage_pass_prefix_keys must be bool, got "
+                f"{type(hicache_storage_pass_prefix_keys).__name__}"
+            )
 
         return (
             extra_config,
@@ -572,37 +898,13 @@ class HiRadixCache(RadixCache):
             )
 
         n_revoke, n_backup, n_release = map(int, qsizes.tolist())
-
+        self._drain_storage_control_queues_impl(
-        # process prefetch revokes
+            n_revoke=n_revoke,
-        for _ in range(n_revoke):
+            n_backup=n_backup,
-            req_id = cc.prefetch_revoke_queue.get()
+            n_release=n_release,
-            info = self.ongoing_prefetch.pop(req_id, None)
+            log_metrics=True,
-            if info is not None:
-                last_host_node, token_ids, _, _ = info
-                last_host_node.release_host()
-                cc.prefetch_tokens_occupied -= len(token_ids)
-            # else: the revoked operation already got terminated, nothing to do
-
-        # process backup acks
-        for _ in range(n_backup):
-            operation = cc.ack_backup_queue.get()
-            ack_id = operation.id
-            entry = self.ongoing_backup.pop(ack_id, None)
-            if entry is not None:
-                entry.release_host()
-            if self.enable_storage_metrics:
-                self.storage_metrics_collector.log_backuped_tokens(
-                    operation.completed_tokens
         )
 
-        # release host memory
-        host_indices_list = []
-        for _ in range(n_release):
-            host_indices_list.append(cc.host_mem_release_queue.get())
-        if host_indices_list:
-            host_indices = torch.cat(host_indices_list, dim=0)
-            cc.mem_pool_host.free(host_indices)
-
     # Timeout is linearly increasing with the number of pages
     def _prefetch_timeout_check_linear_func(self, operation: PrefetchOperation):
         # If hash_value has not been computed in timeout_base seconds, terminate it.

test/registered/hicache/test_hicache_storage_runtime_attach_detach.py

@@ -0,0 +1,368 @@
+"""
+E2E smoke test for HiCache storage runtime attach/detach.
+
+This test launches an SGLang server with hierarchical cache enabled but WITHOUT
+any storage backend at startup, then attaches/detaches a storage backend via the
+HTTP endpoints.
+
+Usage:
+    python3 -m pytest test/registered/hicache/test_hicache_storage_runtime_attach_detach.py -v
+"""
+
+import json
+import os
+import tempfile
+import time
+import unittest
+from urllib import error, request
+
+from sglang.srt.utils import kill_process_tree
+from sglang.test.ci.ci_register import register_cuda_ci
+from sglang.test.test_utils import (
+    DEFAULT_MODEL_NAME_FOR_TEST,
+    DEFAULT_TIMEOUT_FOR_SERVER_LAUNCH,
+    DEFAULT_URL_FOR_TEST,
+    CustomTestCase,
+    find_available_port,
+    popen_launch_server,
+)
+
+register_cuda_ci(est_time=200, suite="stage-b-test-large-2-gpu")
+
+
+class TestHiCacheStorageRuntimeAttachDetach(CustomTestCase):
+    @classmethod
+    def setUpClass(cls):
+        cls.temp_dir = tempfile.mkdtemp()
+        cls.model = DEFAULT_MODEL_NAME_FOR_TEST
+        # Use a per-test-class available port to reduce flakiness / conflicts.
+        default_port = int(DEFAULT_URL_FOR_TEST.rsplit(":", 1)[1])
+        cls.base_url = f"http://127.0.0.1:{find_available_port(default_port)}"
+
+        cls.other_args = [
+            "--enable-hierarchical-cache",
+            "--mem-fraction-static",
+            "0.6",
+            "--hicache-ratio",
+            "1.2",
+            "--hicache-size",
+            "100",
+            "--page-size",
+            "64",
+            "--enable-cache-report",
+            # NOTE: do NOT pass --hicache-storage-backend* here
+        ]
+
+        cls.env = {
+            **os.environ,
+            # File backend uses this env var to decide where to store cache pages.
+            "SGLANG_HICACHE_FILE_BACKEND_STORAGE_DIR": cls.temp_dir,
+            # Make runs less flaky for CI/dev.
+            "SGLANG_ENABLE_DETERMINISTIC_INFERENCE": "1",
+        }
+
+    @classmethod
+    def tearDownClass(cls):
+        import shutil
+
+        shutil.rmtree(cls.temp_dir, ignore_errors=True)
+
+    @classmethod
+    def _wait_for_server_ready(cls, base_url: str, timeout: int = 60) -> bool:
+        start_time = time.time()
+        while time.time() - start_time < timeout:
+            try:
+                code, _body = cls._http_get(f"{base_url}/health", timeout=5)
+                if code == 200:
+                    return True
+            except Exception:
+                pass
+            time.sleep(2)
+        raise TimeoutError("Server failed to start within timeout")
+
+    @staticmethod
+    def _http_get(url: str, timeout: int = 10, headers: dict | None = None):
+        try:
+            req = request.Request(url, headers=headers or {}, method="GET")
+            with request.urlopen(req, timeout=timeout) as resp:
+                return resp.getcode(), resp.read().decode("utf-8", errors="replace")
+        except error.HTTPError as e:
+            body = e.read().decode("utf-8", errors="replace")
+            return e.code, body
+
+    @staticmethod
+    def _http_post_json(url: str, payload: dict | None = None, timeout: int = 30):
+        data = None
+        headers = {}
+        if payload is not None:
+            data = json.dumps(payload).encode("utf-8")
+            headers["Content-Type"] = "application/json"
+        req = request.Request(url, data=data, headers=headers, method="POST")
+        try:
+            with request.urlopen(req, timeout=timeout) as resp:
+                return resp.getcode(), resp.read().decode("utf-8", errors="replace")
+        except error.HTTPError as e:
+            body = e.read().decode("utf-8", errors="replace")
+            return e.code, body
+
+    @staticmethod
+    def _http_post_json_with_headers(
+        url: str,
+        payload: dict | None = None,
+        timeout: int = 30,
+        headers: dict | None = None,
+    ):
+        data = None
+        all_headers = dict(headers or {})
+        if payload is not None:
+            data = json.dumps(payload).encode("utf-8")
+            all_headers["Content-Type"] = "application/json"
+        req = request.Request(url, data=data, headers=all_headers, method="POST")
+        try:
+            with request.urlopen(req, timeout=timeout) as resp:
+                return resp.getcode(), resp.read().decode("utf-8", errors="replace")
+        except error.HTTPError as e:
+            body = e.read().decode("utf-8", errors="replace")
+            return e.code, body
+
+    @staticmethod
+    def _http_put_json_with_headers(
+        url: str,
+        payload: dict | None = None,
+        timeout: int = 30,
+        headers: dict | None = None,
+    ):
+        data = None
+        all_headers = dict(headers or {})
+        if payload is not None:
+            data = json.dumps(payload).encode("utf-8")
+            all_headers["Content-Type"] = "application/json"
+        req = request.Request(url, data=data, headers=all_headers, method="PUT")
+        try:
+            with request.urlopen(req, timeout=timeout) as resp:
+                return resp.getcode(), resp.read().decode("utf-8", errors="replace")
+        except error.HTTPError as e:
+            body = e.read().decode("utf-8", errors="replace")
+            return e.code, body
+
+    @staticmethod
+    def _http_delete_with_headers(
+        url: str, timeout: int = 30, headers: dict | None = None
+    ):
+        all_headers = dict(headers or {})
+        req = request.Request(url, headers=all_headers, method="DELETE")
+        try:
+            with request.urlopen(req, timeout=timeout) as resp:
+                return resp.getcode(), resp.read().decode("utf-8", errors="replace")
+        except error.HTTPError as e:
+            body = e.read().decode("utf-8", errors="replace")
+            return e.code, body
+
+    def _get_backend_status(self, base_url: str, headers: dict | None = None):
+        code, body = self._http_get(
+            f"{base_url}/hicache/storage-backend", timeout=10, headers=headers
+        )
+        self.assertEqual(code, 200, body)
+        return json.loads(body)
+
+    def _attach_backend(
+        self,
+        base_url: str,
+        backend: str,
+        extra_cfg: dict,
+        prefetch_policy: str = "timeout",
+        write_policy: str = "write_through",
+        headers: dict | None = None,
+    ):
+        payload = {
+            "hicache_storage_backend": backend,
+            "hicache_storage_backend_extra_config_json": json.dumps(extra_cfg),
+            "hicache_storage_prefetch_policy": prefetch_policy,
+            "hicache_write_policy": write_policy,
+        }
+        return self._http_put_json_with_headers(
+            f"{base_url}/hicache/storage-backend",
+            payload,
+            timeout=30,
+            headers=headers,
+        )
+
+    def _detach_backend(self, base_url: str, headers: dict | None = None):
+        return self._http_delete_with_headers(
+            f"{base_url}/hicache/storage-backend",
+            timeout=30,
+            headers=headers,
+        )
+
+    def test_runtime_attach_detach(self):
+        # Phase A: WITHOUT --admin-api-key, ADMIN_FORCE endpoints must be forbidden (403).
+        process1 = popen_launch_server(
+            self.model,
+            self.base_url,
+            timeout=DEFAULT_TIMEOUT_FOR_SERVER_LAUNCH,
+            other_args=self.other_args,
+            env=self.env,
+        )
+        try:
+            self._wait_for_server_ready(self.base_url)
+
+            code_info, _body_info = self._http_get(
+                f"{self.base_url}/hicache/storage-backend", timeout=10
+            )
+            self.assertEqual(code_info, 400)
+            code_attach_no_admin, _body_attach_no_admin = self._attach_backend(
+                base_url=self.base_url, backend="file", extra_cfg={}
+            )
+            self.assertEqual(code_attach_no_admin, 400)
+            code_detach_no_admin, _body_detach_no_admin = self._detach_backend(
+                self.base_url
+            )
+            self.assertEqual(code_detach_no_admin, 400)
+        finally:
+            kill_process_tree(process1.pid)
+            time.sleep(2)
+
+        # Phase B: WITH --admin-api-key, must provide Authorization: Bearer <admin_key>.
+        admin_key = "sglang-test-admin-key"
+        base_url2 = f"http://127.0.0.1:{find_available_port(int(self.base_url.rsplit(':', 1)[1]) + 1)}"
+        other_args2 = list(self.other_args) + ["--admin-api-key", admin_key]
+        process2 = popen_launch_server(
+            self.model,
+            base_url2,
+            timeout=DEFAULT_TIMEOUT_FOR_SERVER_LAUNCH,
+            other_args=other_args2,
+            env=self.env,
+        )
+        try:
+            self._wait_for_server_ready(base_url2)
+
+            # 1) Initially disabled (but unauthorized without admin key)
+            code_info2_unauth, _ = self._http_get(
+                f"{base_url2}/hicache/storage-backend", timeout=10
+            )
+            self.assertEqual(code_info2_unauth, 401)
+
+            admin_headers = {"Authorization": f"Bearer {admin_key}"}
+            status0 = self._get_backend_status(base_url2, headers=admin_headers)
+            self.assertIsNone(status0.get("hicache_storage_backend"))
+
+            # 2) Attach should succeed when idle
+            extra_cfg = {
+                "hicache_storage_pass_prefix_keys": True,
+                # keep knobs small and stable
+                "prefetch_threshold": 256,
+                "prefetch_timeout_base": 3,
+                "prefetch_timeout_per_ki_token": 0.01,
+            }
+
+            # Unauthorized attach must fail.
+            code_attach_unauth, _ = self._attach_backend(
+                base_url=base_url2, backend="file", extra_cfg=extra_cfg
+            )
+            self.assertEqual(code_attach_unauth, 401)
+
+            code_attach, body_attach = self._attach_backend(
+                base_url=base_url2,
+                backend="file",
+                extra_cfg=extra_cfg,
+                prefetch_policy="timeout",
+                write_policy="write_back",
+                headers=admin_headers,
+            )
+            self.assertEqual(code_attach, 200, f"{code_attach} - {body_attach}")
+
+            status1 = self._get_backend_status(base_url2, headers=admin_headers)
+            self.assertEqual(status1.get("hicache_storage_backend"), "file")
+            self.assertEqual(
+                status1.get("hicache_storage_backend_extra_config"),
+                json.dumps(extra_cfg),
+            )
+            self.assertEqual(status1.get("hicache_storage_prefetch_policy"), "timeout")
+            self.assertEqual(status1.get("hicache_write_policy"), "write_back")
+
+            # 3) Attach again succeeds with policies updated
+            code_attach_again, body_attach_again = self._attach_backend(
+                base_url=base_url2,
+                backend="file",
+                extra_cfg=extra_cfg,
+                prefetch_policy="wait_complete",
+                write_policy="write_through_selective",
+                headers=admin_headers,
+            )
+            self.assertEqual(
+                code_attach_again, 200, f"{code_attach_again} - {body_attach_again}"
+            )
+
+            status2 = self._get_backend_status(base_url2, headers=admin_headers)
+            self.assertEqual(
+                status2.get("hicache_storage_backend_extra_config"),
+                json.dumps(extra_cfg),
+            )
+            self.assertEqual(
+                status2.get("hicache_storage_prefetch_policy"), "wait_complete"
+            )
+            self.assertEqual(
+                status2.get("hicache_write_policy"), "write_through_selective"
+            )
+
+            # 4) Attach again with different backend should be rejected
+            code_attach_again, body_attach_again = self._attach_backend(
+                base_url=base_url2,
+                backend="mooncake",
+                extra_cfg=extra_cfg,
+                headers=admin_headers,
+            )
+            self.assertNotEqual(code_attach_again, 200, body_attach_again)
+
+            # 5) Detach should succeed and be idempotent
+            code_detach, body_detach = self._detach_backend(
+                base_url2, headers=admin_headers
+            )
+            self.assertEqual(code_detach, 200, f"{code_detach} - {body_detach}")
+            status3 = self._get_backend_status(base_url2, headers=admin_headers)
+            self.assertIsNone(status3.get("hicache_storage_backend"))
+            self.assertEqual(
+                status3.get("hicache_storage_prefetch_policy"), "wait_complete"
+            )
+            self.assertEqual(
+                status3.get("hicache_write_policy"), "write_through_selective"
+            )
+
+            code_detach_again, body_detach_again = self._detach_backend(
+                base_url2, headers=admin_headers
+            )
+            self.assertEqual(
+                code_detach_again,
+                200,
+                f"{code_detach_again} - {body_detach_again}",
+            )
+
+            # 6) Re-attach after detach should succeed
+            code_attach2, body_attach2 = self._attach_backend(
+                base_url=base_url2,
+                backend="file",
+                extra_cfg=extra_cfg,
+                headers=admin_headers,
+            )
+            self.assertEqual(code_attach2, 200, f"{code_attach2} - {body_attach2}")
+            status4 = self._get_backend_status(base_url2, headers=admin_headers)
+            self.assertEqual(status4.get("hicache_storage_backend"), "file")
+            self.assertEqual(
+                status4.get("hicache_storage_backend_extra_config"),
+                json.dumps(extra_cfg),
+            )
+            self.assertEqual(status4.get("hicache_storage_prefetch_policy"), "timeout")
+            self.assertEqual(status4.get("hicache_write_policy"), "write_through")
+
+            # Cleanup: detach for test isolation
+            code_detach2, body_detach2 = self._detach_backend(
+                base_url2, headers=admin_headers
+            )
+            self.assertEqual(code_detach2, 200, f"{code_detach2} - {body_detach2}")
+        finally:
+            kill_process_tree(process2.pid)
+            time.sleep(2)
+
+
+if __name__ == "__main__":
+    unittest.main(verbosity=2)