Hicache Storage Layer Prototype (#7704)

python/sglang/srt/managers/cache_controller.py

@@ -25,6 +25,8 @@ if TYPE_CHECKING:
     from sglang.srt.mem_cache.allocator import BaseTokenToKVPoolAllocator
     from sglang.srt.mem_cache.memory_pool_host import HostKVCache
 
+from sglang.srt.mem_cache.hicache_storage import HiCacheFile, get_hash_str
+
 logger = logging.getLogger(__name__)
 
 
@@ -159,6 +161,57 @@ class TransferBuffer:
         self.buffers.queue.clear()
 
 
+class StorageOperation:
+    counter = 0
+
+    def __init__(
+        self,
+        host_indices: torch.Tensor,
+        token_ids: List[int],
+        last_hash: Optional[str] = None,
+    ):
+        self.host_indices = host_indices
+        self.token_ids = token_ids
+        self.last_hash = last_hash
+        self.completed_tokens = 0
+        self.hash_value = []
+
+        self.id = StorageOperation.counter
+        StorageOperation.counter += 1
+
+    def __lt__(self, other: "StorageOperation"):
+        return self.id < other.id
+
+
+class PrefetchOperation(StorageOperation):
+    def __init__(
+        self,
+        request_id: str,
+        host_indices: torch.Tensor,
+        token_ids: List[int],
+        last_hash: Optional[str] = None,
+    ):
+        self.request_id = request_id
+
+        self._done_flag = False
+        self._lock = threading.Lock()
+
+        super().__init__(host_indices, token_ids, last_hash)
+
+    def increment(self, num_tokens: int):
+        with self._lock:
+            if self._done_flag:
+                return
+            self.completed_tokens += num_tokens
+
+    def mark_done(self):
+        with self._lock:
+            self._done_flag = True
+
+    def is_done(self) -> bool:
+        return self._done_flag
+
+
 class HiCacheController:
 
     def __init__(
@@ -169,6 +222,8 @@ class HiCacheController:
         load_cache_event: threading.Event = None,
         write_policy: str = "write_through_selective",
         io_backend: str = "",
+        storage_backend: Optional[str] = None,
+        prefetch_threshold: int = 256,
     ):
         self.mem_pool_device_allocator = token_to_kv_pool_allocator
         self.mem_pool_device = token_to_kv_pool_allocator.get_kvcache()
@@ -186,6 +241,19 @@ class HiCacheController:
         else:
             self.io_backend = io_backend
 
+        self.enable_storage = False
+        # todo: move backend initialization to storage backend module
+        if storage_backend is not None:
+            if storage_backend == "file":
+                self.storage_backend = HiCacheFile()
+                self.enable_storage = True
+                # todo: threshold policy for prefetching
+                self.prefetch_threshold = prefetch_threshold
+            else:
+                raise NotImplementedError(
+                    f"Unsupported storage backend: {storage_backend}"
+                )
+
         self.load_cache_event = load_cache_event
         self.layer_done_counter = LayerDoneCounter(self.mem_pool_device.layer_num)
         self.mem_pool_device.register_layer_transfer_counter(self.layer_done_counter)
@@ -218,9 +286,26 @@ class HiCacheController:
         self.load_thread = threading.Thread(
             target=self.load_thread_func_layer_by_layer, daemon=True
         )
+
         self.write_thread.start()
         self.load_thread.start()
 
+        if self.enable_storage:
+            self.prefetch_thread = threading.Thread(
+                target=self.prefetch_thread_func, daemon=True
+            )
+            self.backup_thread = threading.Thread(
+                target=self.backup_thread_func, daemon=True
+            )
+            self.prefetch_queue = Queue()
+            self.backup_queue = Queue()
+
+            self.prefetch_revoke_queue = Queue()
+            self.ack_backup_queue = Queue()
+
+            self.prefetch_thread.start()
+            self.backup_thread.start()
+
     def reset(self):
         self.stop_event.set()
         self.write_thread.join()
@@ -232,6 +317,13 @@ class HiCacheController:
         self.load_buffer.clear()
         self.ack_write_queue.queue.clear()
         self.ack_load_queue.queue.clear()
+        if self.enable_storage:
+            self.prefetch_thread.join()
+            self.backup_thread.join()
+            self.prefetch_queue.queue.clear()
+            self.backup_queue.queue.clear()
+            self.prefetch_revoke_queue.queue.clear()
+            self.ack_backup_queue.queue.clear()
 
         self.write_thread = threading.Thread(
             target=self.write_thread_func_direct, daemon=True
@@ -243,6 +335,16 @@ class HiCacheController:
         self.write_thread.start()
         self.load_thread.start()
 
+        if self.enable_storage:
+            self.prefetch_thread = threading.Thread(
+                target=self.prefetch_thread_func, daemon=True
+            )
+            self.backup_thread = threading.Thread(
+                target=self.backup_thread_func, daemon=True
+            )
+            self.prefetch_thread.start()
+            self.backup_thread.start()
+
     def write(
         self,
         device_indices: torch.Tensor,
@@ -383,3 +485,142 @@ class HiCacheController:
             raise ValueError(
                 f"Inconsistent states: {self.mem_pool_host.get_state(host_indices)}"
             )
+
+    def prefetch(
+        self,
+        request_id: str,
+        host_indices: torch.Tensor,
+        new_input_tokens: List[int],
+        last_hash: Optional[str] = None,
+    ) -> int:
+        """
+        Prefetch KV caches from storage backend to host memory.
+        """
+        operation = PrefetchOperation(
+            request_id, host_indices, new_input_tokens, last_hash
+        )
+        self.prefetch_queue.put(operation)
+        return operation
+
+    def terminate_prefetch(self, operation):
+        operation.mark_done()
+        return operation.completed_tokens, operation.hash_value
+
+    def prefetch_io_aux_func(self):
+        """
+        Auxiliary function conducting IO operations for prefetching.
+        """
+        while not self.stop_event.is_set():
+            try:
+                operation = self.prefetch_buffer.get(block=True, timeout=1)
+                for h in operation.hash_value:
+                    page_data = self.storage_backend.get(h)
+                    if page_data is None:
+                        logger.warning(
+                            f"Prefetch operation {operation.request_id} failed to retrieve page {h}."
+                        )
+                        break
+                    self.mem_pool_host.set_from_flat_data_page(
+                        operation.host_indices[operation.completed_tokens],
+                        page_data,
+                    )
+                    operation.increment(self.page_size)
+                    if operation.is_done():
+                        # operation terminated by controller, release pre-allocated memory
+                        self.mem_pool_host.free(
+                            operation.host_indices[operation.completed_tokens :]
+                        )
+                        break
+            except Empty:
+                continue
+
+    def prefetch_thread_func(self):
+        """
+        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)
+        aux_thread.start()
+        while (not self.stop_event.is_set()) or not self.prefetch_queue.empty():
+            try:
+                operation = self.prefetch_queue.get(block=True, timeout=1)
+                if operation is None:
+                    continue
+
+                last_hash = operation.last_hash
+                tokens_to_fetch = operation.token_ids
+
+                storage_hit_count = 0
+                remaining_tokens = len(tokens_to_fetch)
+                hash_value = []
+                while remaining_tokens >= self.page_size:
+                    last_hash = get_hash_str(
+                        tokens_to_fetch[
+                            storage_hit_count : storage_hit_count + self.page_size
+                        ],
+                        last_hash,
+                    )
+                    if self.storage_backend.exists(last_hash):
+                        storage_hit_count += self.page_size
+                        hash_value.append(last_hash)
+                        remaining_tokens -= self.page_size
+                    else:
+                        break
+
+                if storage_hit_count < self.prefetch_threshold:
+                    # not to prefetch if not enough benefits
+                    self.prefetch_revoke_queue.put(operation.request_id)
+                else:
+                    operation.hash_value = hash_value
+                    logger.debug(
+                        f"Prefetching {len(hash_value)} pages for request {operation.request_id}."
+                    )
+                    self.prefetch_buffer.put(operation)
+
+            except Empty:
+                continue
+
+    def write_storage(
+        self,
+        host_indices: torch.Tensor,
+        token_ids: List[int],
+        last_hash: Optional[str] = None,
+    ) -> int:
+        """
+        Write KV caches from host memory to storage backend.
+        """
+        operation = StorageOperation(host_indices, token_ids, last_hash)
+        self.backup_queue.put(operation)
+        return operation.id
+
+    def backup_thread_func(self):
+        """
+        Manage backup operations from host memory to storage backend.
+        """
+        while not self.stop_event.is_set():
+            try:
+                operation = self.backup_queue.get(block=True, timeout=1)
+                if operation is None:
+                    continue
+
+                last_hash = operation.last_hash
+                tokens_to_backup = operation.token_ids
+
+                for i in range(0, len(tokens_to_backup), self.page_size):
+                    last_hash = get_hash_str(
+                        tokens_to_backup[i : i + self.page_size], last_hash
+                    )
+                    # todo, handle failures in storage backend
+                    self.storage_backend.set(
+                        last_hash,
+                        self.mem_pool_host.get_flat_data_page(
+                            operation.host_indices[i]
+                        ),
+                    )
+                    operation.completed_tokens += self.page_size
+                    operation.hash_value.append(last_hash)
+
+                self.ack_backup_queue.put((operation.id, operation.hash_value))
+
+            except Empty:
+                continue

python/sglang/srt/managers/scheduler.py

@@ -262,6 +262,7 @@ class Scheduler(
         )
         self.gpu_id = gpu_id
         self.enable_hierarchical_cache = server_args.enable_hierarchical_cache
+        self.enable_hicache_storage = server_args.hicache_storage_backend is not None
         self.page_size = server_args.page_size
         self.dp_size = server_args.dp_size
         self.attn_tp_rank, self.attn_tp_size, self.attn_dp_rank = (
@@ -614,6 +615,7 @@ class Scheduler(
                         == "fa3"  # hot fix for incompatibility
                         else server_args.hicache_io_backend
                     ),
+                    hicache_storage_backend=server_args.hicache_storage_backend,
                 )
                 self.tp_worker.register_hicache_layer_transfer_counter(
                     self.tree_cache.cache_controller.layer_done_counter
@@ -1258,6 +1260,15 @@ class Scheduler(
         elif self.disaggregation_mode == DisaggregationMode.DECODE:
             self.disagg_decode_prealloc_queue.add(req)
         else:
+            if self.enable_hicache_storage:
+                req.init_next_round_input(self.tree_cache)
+                last_hash = req.last_host_node.get_last_hash_value()
+                matched_len = len(req.prefix_indices) + req.host_hit_length
+                if (matched_len > 0 and last_hash is not None) or matched_len == 0:
+                    new_input_tokens = req.fill_ids[matched_len:]
+                    self.tree_cache.prefetch_from_storage(
+                        req.rid, req.last_host_node, new_input_tokens, last_hash
+                    )
             self.waiting_queue.append(req)
 
     def _extend_requests_to_queue(self, reqs: List[Req], is_retracted: bool = False):
@@ -1731,6 +1742,9 @@ class Scheduler(
                     self.running_batch.batch_is_full = True
                     break
 
+            if self.enable_hicache_storage:
+                self.tree_cache.check_prefetch_progress(req.rid)
+
             req.init_next_round_input(self.tree_cache)
             res = adder.add_one_req(req, has_chunked_req=(self.chunked_req is not None))
 

python/sglang/srt/mem_cache/hicache_storage.py

@@ -0,0 +1,152 @@
+import hashlib
+import logging
+import os
+from abc import ABC, abstractmethod
+from typing import List, Optional
+
+import torch
+
+logger = logging.getLogger(__name__)
+
+
+def get_hash_str(token_ids: List[int], prior_hash: Optional[str] = None) -> str:
+    hasher = hashlib.sha256()
+
+    if prior_hash:
+        hasher.update(bytes.fromhex(prior_hash))
+
+    for t in token_ids:
+        hasher.update(t.to_bytes(4, byteorder="little", signed=False))
+
+    return hasher.hexdigest()
+
+
+class HiCacheStorage(ABC):
+    """
+    HiCacheStorage is a class that provides a generic key-value interface for storing and retrieving KV cache.
+    It abstracts the underlying storage mechanism, allowing different implementations to be used.
+    """
+
+    # todo, translate tensor object access for different TP ranks
+    # potentially pass model and TP configs into storage backend
+    # todo, the page size of storage backend does not have to be the same as the same as host memory pool
+
+    @abstractmethod
+    def get(
+        self, key: str, target_location: Optional[torch.Tensor] = None
+    ) -> torch.Tensor | None:
+        """
+        Retrieve the value associated with the given key.
+        Returns None if the key does not exist.
+        """
+        pass
+
+    @abstractmethod
+    def batch_get(
+        self, keys: List[str], target_locations: Optional[List[torch.Tensor]] = None
+    ) -> List[torch.Tensor | None]:
+        """
+        Retrieve values for multiple keys.
+        Returns a list of tensors or None for each key.
+        """
+        pass
+
+    @abstractmethod
+    def set(self, key, value) -> bool:
+        """
+        Store the value associated with the given key.
+        Returns True if the operation was successful, False otherwise.
+        """
+        pass
+
+    @abstractmethod
+    def batch_set(self, keys: List[str], values: List[torch.Tensor]) -> bool:
+        """
+        Store multiple key-value pairs.
+        Returns True if all operations were successful, False otherwise.
+        """
+        pass
+
+    @abstractmethod
+    def exists(self, key: str) -> bool:
+        """
+        Check if the key exists in the storage.
+        Returns True if the key exists, False otherwise.
+        """
+        pass
+
+
+class HiCacheFile(HiCacheStorage):
+
+    def __init__(self, file_path: str = "/tmp/hicache"):
+        self.file_path = file_path
+        if not os.path.exists(self.file_path):
+            os.makedirs(self.file_path)
+            logger.info(f"Created HiCacheFile storage directory at {self.file_path}")
+
+    def get(
+        self, key: str, target_location: Optional[torch.Tensor] = None
+    ) -> torch.Tensor | None:
+        tensor_path = os.path.join(self.file_path, f"{key}.bin")
+        try:
+            # todo: fixing the target_location logic to enable in-place loading
+            loaded_tensor = torch.load(tensor_path)
+            if isinstance(loaded_tensor, torch.Tensor):
+                return loaded_tensor
+            else:
+                logger.error(f"Loaded data for key {key} is not a tensor.")
+                return None
+        except FileNotFoundError:
+            return None
+
+    def batch_get(
+        self,
+        keys: List[str],
+        target_locations: Optional[List[torch.Tensor]] = None,
+    ) -> List[torch.Tensor | None]:
+        return [
+            self.get(key, target_location)
+            for key, target_location in zip(
+                keys, target_locations or [None] * len(keys)
+            )
+        ]
+
+    def set(self, key: str, value: torch.Tensor) -> bool:
+        tensor_path = os.path.join(self.file_path, f"{key}.bin")
+        if self.exists(key):
+            logger.debug(f"Key {key} already exists. Skipped.")
+            return True
+        try:
+            torch.save(value, tensor_path)
+            return True
+        except Exception as e:
+            logger.error(f"Failed to save tensor {key}: {e}")
+            return False
+
+    def batch_set(self, keys: List[str], values: List[torch.Tensor]) -> bool:
+        for key, value in zip(keys, values):
+            if not self.set(key, value):
+                return False
+        return True
+
+    def exists(self, key: str) -> bool:
+        tensor_path = os.path.join(self.file_path, f"{key}.bin")
+        return os.path.exists(tensor_path)
+
+    def delete(self, key: str) -> None:
+        tensor_path = os.path.join(self.file_path, f"{key}.bin")
+        try:
+            os.remove(tensor_path)
+        except FileNotFoundError:
+            logger.warning(f"Key {key} does not exist. Cannot delete.")
+            return
+
+    def clear(self) -> None:
+        try:
+            for filename in os.listdir(self.file_path):
+                file_path = os.path.join(self.file_path, filename)
+                if os.path.isfile(file_path):
+                    os.remove(file_path)
+            logger.info("Cleared all entries in HiCacheFile storage.")
+        except Exception as e:
+            logger.error(f"Failed to clear HiCacheFile storage: {e}")

python/sglang/srt/mem_cache/hiradix_cache.py

@@ -35,6 +35,7 @@ class HiRadixCache(RadixCache):
         hicache_size: int,
         hicache_write_policy: str,
         hicache_io_backend: str,
+        hicache_storage_backend: Optional[str] = None,
     ):
         self.kv_cache = token_to_kv_pool_allocator.get_kvcache()
         if isinstance(self.kv_cache, MHATokenToKVPool):
@@ -49,6 +50,9 @@ class HiRadixCache(RadixCache):
             raise ValueError(f"HiRadixCache only supports MHA and MLA yet")
 
         self.tp_group = tp_cache_group
+        self.enable_storage = hicache_storage_backend is not None
+        # todo: customizable storage prefetch threshold
+        self.prefetch_threshold = 256
 
         self.load_cache_event = threading.Event()
         self.cache_controller = HiCacheController(
@@ -58,16 +62,22 @@ class HiRadixCache(RadixCache):
             load_cache_event=self.load_cache_event,
             write_policy=hicache_write_policy,
             io_backend=hicache_io_backend,
+            storage_backend=hicache_storage_backend,
+            prefetch_threshold=self.prefetch_threshold,
         )
 
         # record the nodes with ongoing write through
         self.ongoing_write_through = {}
         # record the node segments with ongoing load back
         self.ongoing_load_back = {}
+        # record the ongoing prefetch requests
+        self.ongoing_prefetch = {}
+        self.ongoing_backup = {}
         # todo: dynamically adjust the threshold
         self.write_through_threshold = (
             1 if hicache_write_policy == "write_through" else 3
         )
+        self.write_through_threshold_storage = 3
         self.load_back_threshold = 10
         super().__init__(
             req_to_token_pool, token_to_kv_pool_allocator, page_size, disable=False
@@ -108,13 +118,30 @@ class HiRadixCache(RadixCache):
 
         return len(host_indices)
 
+    def write_backup_storage(self, node: TreeNode):
+        operation_id = self.cache_controller.write_storage(
+            node.host_value, node.key, node.parent.get_last_hash_value()
+        )
+        self.ongoing_backup[operation_id] = node
+        node.protect_host()
+
     def inc_hit_count(self, node: TreeNode):
-        if node.backuped or self.cache_controller.write_policy == "write_back":
+        if self.cache_controller.write_policy == "write_back":
             return
         node.hit_count += 1
-        if node.hit_count >= self.write_through_threshold:
-            self.write_backup(node)
-            node.hit_count = 0
+
+        if not node.backuped:
+            if node.hit_count >= self.write_through_threshold:
+                # write to host if the node is not backuped
+                self.write_backup(node)
+        else:
+            if (
+                self.enable_storage
+                and (not node.backuped_storage)
+                and node.hit_count >= self.write_through_threshold_storage
+            ):
+                # if the node is backuped on host memory but not on storage
+                self.write_backup_storage(node)
 
     def writing_check(self, write_back=False):
         if write_back:
@@ -221,6 +248,10 @@ class HiRadixCache(RadixCache):
             if not x.evicted:
                 continue
 
+            # node is protected from eviction as it has ongoing prefetch or backup to storage
+            if x.host_ref_counter > 0:
+                continue
+
             num_evicted += self.cache_controller.evict_host(x.host_value)
 
             for k, v in x.parent.children.items():
@@ -314,6 +345,85 @@ class HiRadixCache(RadixCache):
     def check_hicache_events(self):
         self.writing_check()
         self.loading_check()
+        if self.enable_storage:
+            self.check_revoked_prefetch()
+            self.check_backup_progress()
+
+    def check_revoked_prefetch(self):
+        queue_size = torch.tensor(
+            self.cache_controller.prefetch_revoke_queue.qsize(), dtype=torch.int
+        )
+        if torch.distributed.get_world_size(group=self.tp_group) > 1:
+            # synchrnoize TP workers to make the same update to hiradix cache
+            torch.distributed.all_reduce(
+                queue_size,
+                op=torch.distributed.ReduceOp.MIN,
+                group=self.tp_group,
+            )
+        for _ in range(queue_size.item()):
+            req_id = self.cache_controller.prefetch_revoke_queue.get()
+            if req_id in self.ongoing_prefetch:
+                last_host_node, _, host_indices, _ = self.ongoing_prefetch[req_id]
+                last_host_node.release_host()
+                self.cache_controller.mem_pool_host.free(host_indices)
+                del self.ongoing_prefetch[req_id]
+
+    def check_backup_progress(self):
+        queue_size = torch.tensor(
+            self.cache_controller.ack_backup_queue.qsize(), dtype=torch.int
+        )
+        if torch.distributed.get_world_size(group=self.tp_group) > 1:
+            # synchrnoize TP workers to make the same update to hiradix cache
+            torch.distributed.all_reduce(
+                queue_size,
+                op=torch.distributed.ReduceOp.MIN,
+                group=self.tp_group,
+            )
+        for _ in range(queue_size.item()):
+            ack_id, hash_value = self.cache_controller.ack_backup_queue.get()
+            self.ongoing_backup[ack_id].hash_value = hash_value
+            self.ongoing_backup[ack_id].release_host()
+            del self.ongoing_backup[ack_id]
+
+    def check_prefetch_progress(self, req_id: str):
+        if req_id not in self.ongoing_prefetch:
+            # there is no ongoing prefetch for this request or it has been revoked
+            return
+
+        # todo: more policies for prefetch progress such as timeout
+        # the current policy is to prefetch with best effort and terminate when queuing is over
+        last_host_node, token_ids, host_indices, operation = self.ongoing_prefetch[
+            req_id
+        ]
+        completed_tokens, hash_value = self.cache_controller.terminate_prefetch(
+            operation
+        )
+        logger.debug(f"Prefetch {req_id} completed with {completed_tokens} tokens")
+
+        min_completed_tokens = torch.tensor(completed_tokens, dtype=torch.int)
+        if torch.distributed.get_world_size(group=self.tp_group) > 1:
+            # synchrnoize TP workers to make the same update to hiradix cache
+            torch.distributed.all_reduce(
+                min_completed_tokens,
+                op=torch.distributed.ReduceOp.MIN,
+                group=self.tp_group,
+            )
+        min_completed_tokens = min_completed_tokens.item()
+        fetched_token_ids = token_ids[:min_completed_tokens]
+        written_indices = host_indices[:min_completed_tokens]
+        matched_length = self._insert_helper_host(
+            last_host_node,
+            fetched_token_ids,
+            written_indices,
+            hash_value[:min_completed_tokens],
+        )
+
+        self.cache_controller.mem_pool_host.free(host_indices[:matched_length])
+        self.cache_controller.mem_pool_host.free(
+            host_indices[min_completed_tokens:completed_tokens]
+        )
+        last_host_node.release_host()
+        del self.ongoing_prefetch[req_id]
 
     def match_prefix(self, key: List[int], **kwargs):
         empty_value = torch.empty((0,), dtype=torch.int64, device=self.device)
@@ -348,6 +458,71 @@ class HiRadixCache(RadixCache):
             host_hit_length=host_hit_length,
         )
 
+    def prefetch_from_storage(
+        self,
+        req_id: str,
+        last_host_node: TreeNode,
+        new_input_tokens: List[int],
+        last_hash: Optional[str] = None,
+    ):
+        if not self.enable_storage or len(new_input_tokens) < self.prefetch_threshold:
+            return
+
+        last_host_node.protect_host()
+        host_indices = self.cache_controller.mem_pool_host.alloc(len(new_input_tokens))
+        if host_indices is None:
+            self.evict_host(len(new_input_tokens))
+            host_indices = self.cache_controller.mem_pool_host.alloc(
+                len(new_input_tokens)
+            )
+        if host_indices is None:
+            last_host_node.release_host()
+            # no sufficient host memory to prefetch
+            return
+        operation = self.cache_controller.prefetch(
+            req_id, host_indices, new_input_tokens, last_hash
+        )
+        self.ongoing_prefetch[req_id] = (
+            last_host_node,
+            new_input_tokens,
+            host_indices,
+            operation,
+        )
+
+    def _insert_helper_host(self, node: TreeNode, key: List, host_value, hash_value):
+        node.last_access_time = time.monotonic()
+        if len(key) == 0:
+            return 0
+
+        child_key = self.get_child_key_fn(key)
+
+        matched_length = 0
+        while len(key) > 0 and child_key in node.children.keys():
+            node = node.children[child_key]
+            node.last_access_time = time.monotonic()
+            prefix_len = self.key_match_fn(node.key, key)
+            key = key[prefix_len:]
+            host_value = host_value[prefix_len:]
+            hash_value = hash_value[prefix_len:]
+            matched_length += prefix_len
+
+            if prefix_len < len(node.key):
+                new_node = self._split_node(node.key, node, prefix_len)
+                node = new_node
+
+            if len(key):
+                child_key = self.get_child_key_fn(key)
+
+        if len(key):
+            new_node = TreeNode()
+            new_node.parent = node
+            new_node.key = key
+            new_node.value = None
+            new_node.host_value = host_value
+            new_node.hash_value = hash_value
+            node.children[child_key] = new_node
+        return matched_length
+
     def _match_prefix_helper(self, node: TreeNode, key: List):
         node.last_access_time = time.monotonic()
         child_key = self.get_child_key_fn(key)

python/sglang/srt/mem_cache/memory_pool_host.py

@@ -99,6 +99,20 @@ class HostKVCache(abc.ABC):
     def init_kv_buffer(self):
         raise NotImplementedError()
 
+    @abc.abstractmethod
+    def get_flat_data_page(self, index) -> torch.Tensor:
+        """
+        Get a flat data page from the host memory pool.
+        """
+        raise NotImplementedError()
+
+    @abc.abstractmethod
+    def set_from_flat_data_page(self, index: int, data_page: torch.Tensor) -> None:
+        """
+        Set a flat data page to the host memory pool.
+        """
+        raise NotImplementedError()
+
     @synchronized()
     def clear(self):
         # Initialize memory states and tracking structures.
@@ -227,6 +241,19 @@ class MHATokenToKVPoolHost(HostKVCache):
             pin_memory=self.pin_memory,
         )
 
+    # todo, page first memory layout
+    def get_flat_data_page(self, index) -> torch.Tensor:
+        return self.kv_buffer[:, :, index : index + self.page_size, :, :].flatten()
+
+    def set_from_flat_data_page(self, index: int, data_page: torch.Tensor) -> None:
+        self.kv_buffer[:, :, index : index + self.page_size, :, :] = data_page.reshape(
+            2,
+            self.layer_num,
+            self.page_size,
+            self.head_num,
+            self.head_dim,
+        )
+
     @property
     def k_buffer(self):
         return self.kv_buffer[0]
@@ -276,3 +303,14 @@ class MLATokenToKVPoolHost(HostKVCache):
             device=self.device,
             pin_memory=self.pin_memory,
         )
+
+    def get_flat_data_page(self, index) -> torch.Tensor:
+        return self.kv_buffer[:, index : index + self.page_size, :, :].flatten()
+
+    def set_from_flat_data_page(self, index: int, data_page: torch.Tensor) -> None:
+        self.kv_buffer[:, index : index + self.page_size, :, :] = data_page.reshape(
+            self.layer_num,
+            self.page_size,
+            1,
+            self.kv_lora_rank + self.qk_rope_head_dim,
+        )

python/sglang/srt/mem_cache/radix_cache.py

@@ -55,8 +55,13 @@ class TreeNode:
         self.hit_count = 0
         # indicating the node is loading KV cache from host
         self.loading = False
+        # indicating the node is locked to protect from eviction
+        # incremented when the node is referenced by a storage operation
+        self.host_ref_counter = 0
         # store the host indices of KV cache
         self.host_value: Optional[torch.Tensor] = None
+        # store hash values of each pages
+        self.hash_value: Optional[List[str]] = None
 
         self.id = TreeNode.counter if id is None else id
         TreeNode.counter += 1
@@ -69,6 +74,27 @@ class TreeNode:
     def backuped(self):
         return self.host_value is not None
 
+    @property
+    def backuped_storage(self):
+        return self.hash_value is not None and len(self.hash_value) > 0
+
+    def protect_host(self):
+        """Protect the host value from eviction."""
+        self.host_ref_counter += 1
+
+    def release_host(self):
+        """Release the host value, allowing it to be evicted."""
+        if self.host_ref_counter > 0:
+            self.host_ref_counter -= 1
+        else:
+            raise RuntimeError("Host reference counter is already zero.")
+
+    def get_last_hash_value(self) -> Optional[str]:
+        """Returns the hash value of the last page in this node."""
+        if self.hash_value is None or len(self.hash_value) == 0:
+            return None
+        return self.hash_value[-1]
+
     def __lt__(self, other: "TreeNode"):
         return self.last_access_time < other.last_access_time
 

python/sglang/srt/server_args.py

@@ -222,6 +222,7 @@ class ServerArgs:
     hicache_size: int = 0
     hicache_write_policy: str = "write_through_selective"
     hicache_io_backend: str = ""
+    hicache_storage_backend: Optional[str] = None
     flashinfer_mla_disable_ragged: bool = False
     disable_shared_experts_fusion: bool = False
     disable_chunked_prefix_cache: bool = False
@@ -1604,6 +1605,13 @@ class ServerArgs:
             default=ServerArgs.hicache_io_backend,
             help="The IO backend for KV cache transfer between CPU and GPU",
         )
+        parser.add_argument(
+            "--hicache-storage-backend",
+            type=str,
+            choices=["file"],  # todo, mooncacke
+            default=ServerArgs.hicache_storage_backend,
+            help="The storage backend for hierarchical KV cache.",
+        )
         parser.add_argument(
             "--flashinfer-mla-disable-ragged",
             action="store_true",