[PD]: Support HiCache prefetching and pd-incremental transfer on decode side (#26227)

Co-authored-by: huangtingwei <141888744+huangtingwei9988@users.noreply.github.com>
Co-authored-by: Shangming Cai <csmthu@gmail.com>
Co-authored-by: 晟海 <huangtingwei.htw@antgroup.com>

python/sglang/srt/disaggregation/decode.py

@@ -25,7 +25,7 @@ import time
 from collections import deque
 from dataclasses import dataclass
 from http import HTTPStatus
-from typing import TYPE_CHECKING, Dict, List, Optional, Tuple
+from typing import TYPE_CHECKING, Any, Dict, List, Optional, Tuple
 
 import numpy as np
 import torch
@@ -36,6 +36,13 @@ from sglang.srt.constants import GPU_MEMORY_TYPE_KV_CACHE
 from sglang.srt.disaggregation.base import KVPoll
 from sglang.srt.disaggregation.base.conn import StateType
 from sglang.srt.disaggregation.common.conn import CommonKVManager, CommonKVReceiver
+from sglang.srt.disaggregation.decode_hicache_mixin import (
+    DecodeHiCachePreallocMixin,
+    DecodeHiCacheTransferMixin,
+    DecodePrefixMatch,
+    HiCacheRestoreGatedKVReceiver,
+    HiCacheRestoreResult,
+)
 from sglang.srt.disaggregation.utils import (
     DisaggregationMode,
     KVClassType,
@@ -56,7 +63,10 @@ from sglang.srt.managers.schedule_batch import FINISH_ABORT, ScheduleBatch
 from sglang.srt.managers.schedule_policy import match_prefix_for_req
 from sglang.srt.managers.utils import GenerationBatchResult
 from sglang.srt.mem_cache.allocator import BaseTokenToKVPoolAllocator
-from sglang.srt.mem_cache.base_prefix_cache import BasePrefixCache, EvictParams
+from sglang.srt.mem_cache.base_prefix_cache import (
+    BasePrefixCache,
+    EvictParams,
+)
 from sglang.srt.mem_cache.common import (
     kv_to_page_indices,
     page_align_floor,
@@ -241,6 +251,13 @@ class DecodeRequest:
     waiting_for_input: bool = False
     metadata_buffer_index: int = -1
 
+    # HiCache Status
+    prefix_match: Optional[DecodePrefixMatch] = None
+    hicache_restored_kv_indices: Optional[torch.Tensor] = None
+    hicache_restored_node: Any = None
+    hicache_load_consumer_index: int = -1
+    hicache_restore_status: HiCacheRestoreResult = HiCacheRestoreResult.PENDING
+
     @property
     def seqlen(self) -> int:
         return self.req.seqlen
@@ -250,7 +267,7 @@ class DecodeRequest:
         return self.req.priority
 
 
-class DecodePreallocQueue:
+class DecodePreallocQueue(DecodeHiCachePreallocMixin):
     """
     Store the requests that are preallocating.
     """
@@ -458,7 +475,7 @@ class DecodePreallocQueue:
 
             self.pending_reqs.append(decode_req)
 
-    def _match_prefix_and_lock(self, req: Req) -> Tuple[torch.Tensor, int]:
+    def _match_prefix_and_lock(self, req: Req) -> DecodePrefixMatch:
         """
         Match a request against the decode-side radix cache, lock the matched
         node to prevent eviction, and return the matched prefix information.
@@ -470,12 +487,9 @@ class DecodePreallocQueue:
             cow_mamba=self.tree_cache.supports_mamba(),
             include_req=True,
         )
-        prefix_indices = result.device_indices
-        last_device_node = result.last_device_node
         # Always lock to match aggregated scheduling behavior
-        self.tree_cache.inc_lock_ref(last_device_node)
+        self.tree_cache.inc_lock_ref(result.last_device_node)
-
+        return self._build_decode_prefix_match(req, result)
-        return prefix_indices, len(prefix_indices)
 
     def _resolve_prefill_dp_rank(self, req: Req) -> Optional[int]:
         prefill_info = self.kv_manager.prefill_info_table.get(_bootstrap_addr(req))
@@ -756,7 +770,8 @@ class DecodePreallocQueue:
             full_allocatable_tokens = self._allocatable_token_budgets(
                 retractable_tokens=retractable_tokens, count_retracted=True
             )
-
+        reserved_restore_tokens = self._hicache_pending_restore_tokens()
+        full_allocatable_tokens -= reserved_restore_tokens
         # Sort by priority before any index-based bookkeeping so that both the
         # abort-scan loop and the preallocation loop operate on the same order.
         if self.scheduler.enable_priority_scheduling:
@@ -815,15 +830,18 @@ class DecodePreallocQueue:
             # Memory estimation: don't add if the projected memory cannot be met
             # TODO: add new_token ratio
             origin_input_len = len(decode_req.req.origin_input_ids)
+            prefix_match: Optional[DecodePrefixMatch] = None
             if self.scheduler.server_args.disaggregation_decode_enable_radix_cache:
                 # Match prefix against decode's radix cache.
-                prefix_indices, prefix_len = self._match_prefix_and_lock(decode_req.req)
+                prefix_match = self._match_prefix_and_lock(decode_req.req)
-                # Align prefix_len down to page boundary so both prefill and
+                prefix_indices = prefix_match.prefix_indices
-                # decode agree on the page-aligned split point for KV transfer.
+                # prefix_len: tokens already on device (L1 hit).
-                page_size = self.token_to_kv_pool_allocator.page_size
+                # total_prefix_len: full prefix promised to prefill
-                if page_size > 1 and prefix_len % page_size != 0:
+                # (L1 + L2 host hit + L3 storage hit), sent as PD
-                    prefix_len = page_align_floor(prefix_len, page_size)
+                # protocol's `decode_prefix_len`. The [prefix_len, total)
-                    prefix_indices = prefix_indices[:prefix_len]
+                # gap is filled by HiCache loadback later.
+                prefix_len = prefix_match.l1_prefix_len
+                total_prefix_len = prefix_match.decode_prefix_len
 
                 fill_len = origin_input_len + max(len(decode_req.req.output_ids) - 1, 0)
                 required_alloc_tokens = self._required_alloc_tokens(
@@ -836,10 +854,12 @@ class DecodePreallocQueue:
                     retractable_tokens=retractable_tokens,
                     count_retracted=True,
                     extra_reserved_reqs=len(preallocated_reqs),
+                    hicache_reserved_tokens=reserved_restore_tokens,
                 )
             else:
                 prefix_indices = None
                 prefix_len = 0
+                total_prefix_len = 0
                 required_alloc_tokens = origin_input_len
 
             required_tokens_for_request = (
@@ -885,20 +905,31 @@ class DecodePreallocQueue:
                         self.tree_cache.dec_lock_ref(decode_req.req.last_node)
                     break
 
-            dst_kv_indices = self._pre_alloc(decode_req.req, prefix_indices, prefix_len)
+            dst_kv_indices = self._pre_alloc(
+                decode_req.req,
+                prefix_indices,
+                prefix_len,
+                total_prefix_len,
+            )
+            decode_req.prefix_match = prefix_match
+            if self.scheduler.enable_decode_hicache:
+                self._start_hicache_prefetch(decode_req.req, prefix_match)
             hisparse_req_budget -= 1
             # Recompute from actual pool state for the next queue entry.
             # This accounts for page rounding and newly locked evictable cache.
+            if prefix_match is not None:
+                reserved_restore_tokens += prefix_match.restore_token_count
             full_allocatable_tokens = self._allocatable_token_budgets(
                 retractable_tokens=retractable_tokens,
                 count_retracted=True,
                 extra_reserved_reqs=len(preallocated_reqs) + 1,
+                hicache_reserved_tokens=reserved_restore_tokens,
             )
             if uses_swa_tail_prealloc:
                 # SWA budget uses simple decrement (no radix cache eviction in
                 # the SWA pool, so page-rounding drift is negligible).
                 swa_allocatable_tokens -= swa_required
-            decode_req.req.cache_protected_len = prefix_len
+            decode_req.req.cache_protected_len = total_prefix_len
 
             page_size = self.token_to_kv_pool_allocator.page_size
             if self.scheduler.enable_hisparse:
@@ -913,7 +944,7 @@ class DecodePreallocQueue:
                 # Only send delta indices (beyond prefix) to prefill.
                 kv_indices = (
                     self.req_to_token_pool.req_to_token[decode_req.req.req_pool_idx][
-                        prefix_len:origin_input_len
+                        total_prefix_len:origin_input_len
                     ]
                     .cpu()
                     .numpy()
@@ -977,7 +1008,7 @@ class DecodePreallocQueue:
                 page_indices,
                 decode_req.metadata_buffer_index,
                 state_indices,
-                decode_prefix_len=prefix_len,
+                decode_prefix_len=total_prefix_len,
             )
             if (
                 self.transfer_queue.enable_staging
@@ -1065,6 +1096,7 @@ class DecodePreallocQueue:
         count_retracted: bool = True,
         extra_reserved_reqs: int = 0,
         reserved_tokens: Optional[int] = None,
+        hicache_reserved_tokens: int = 0,
     ) -> int:
         need_space_for_single_req = self._need_space_for_single_req(retractable_tokens)
         if reserved_tokens is None:
@@ -1107,6 +1139,7 @@ class DecodePreallocQueue:
                 full_required, _ = self._prealloc_required_tokens(req)
                 allocatable_tokens -= full_required
 
+        allocatable_tokens -= hicache_reserved_tokens
         return allocatable_tokens
 
     def _swa_tail_allocatable_token_budget(
@@ -1189,10 +1222,20 @@ class DecodePreallocQueue:
         req: Req,
         prefix_indices: Optional[torch.Tensor] = None,
         prefix_len: Optional[int] = None,
+        total_prefix_len: Optional[int] = None,
     ) -> torch.Tensor:
-        """Pre-allocate the memory for req_to_token and token_kv_pool"""
+        """Pre-allocate the memory for req_to_token and token_kv_pool.
+
+        ``prefix_len`` is the L1 device-resident prefix length (already
+        backed by ``prefix_indices``). ``total_prefix_len`` is the full
+        prefix committed to prefill as ``decode_prefix_len`` (L1 + L2 + L3);
+        the ``[prefix_len, total_prefix_len)`` gap is filled later by HiCache
+        loadback.
+        """
         if prefix_len is None:
             prefix_len = 0
+        if total_prefix_len is None:
+            total_prefix_len = prefix_len
 
         req_pool_indices = self.req_to_token_pool.alloc([req])
 
@@ -1212,7 +1255,7 @@ class DecodePreallocQueue:
         # TODO(retraction): when retraction is implemented with radix cache
         # awareness, a retracted request should re-match the tree here
         # instead of re-allocating from scratch. See resume_retracted_reqs.
-        delta_len = fill_len - prefix_len
+        delta_len = fill_len - total_prefix_len
         required_alloc_tokens = self._required_alloc_tokens(
             fill_len=fill_len, prefix_len=prefix_len
         )
@@ -1233,7 +1276,8 @@ class DecodePreallocQueue:
                     f"after evicting {result.num_tokens_evicted}/{num_to_evict} tokens. "
                     f"evictable_size={self.tree_cache.evictable_size()}, "
                     f"protected_size={self.tree_cache.protected_size()}, "
-                    f"fill_len={fill_len}, prefix_len={prefix_len}, delta_len={delta_len}, "
+                    f"fill_len={fill_len}, prefix_len={prefix_len}, "
+                    f"total_prefix_len={total_prefix_len}, delta_len={delta_len}, "
                     f"page_size={self.token_to_kv_pool_allocator.page_size}, "
                     f"req={req.rid}"
                 )
@@ -1289,9 +1333,9 @@ class DecodePreallocQueue:
             else:
                 kv_loc = self.token_to_kv_pool_allocator.alloc_extend(
                     prefix_lens=torch.tensor(
-                        [prefix_len], dtype=torch.int64, device=device
+                        [total_prefix_len], dtype=torch.int64, device=device
                     ),
-                    prefix_lens_cpu=torch.tensor([prefix_len], dtype=torch.int64),
+                    prefix_lens_cpu=torch.tensor([total_prefix_len], dtype=torch.int64),
                     seq_lens=torch.tensor([fill_len], dtype=torch.int64, device=device),
                     seq_lens_cpu=torch.tensor([fill_len], dtype=torch.int64),
                     last_loc=last_loc,
@@ -1304,13 +1348,17 @@ class DecodePreallocQueue:
             f"evictable={self.tree_cache.evictable_size()}, "
             f"protected={self.tree_cache.protected_size()}, "
             f"required_alloc={required_alloc_tokens}, delta={delta_len}, "
-            f"fill={fill_len}, prefix={prefix_len}, "
+            f"fill={fill_len}, prefix={prefix_len}, total_prefix={total_prefix_len}, "
             f"page_size={self.token_to_kv_pool_allocator.page_size}, "
             f"req={req.rid}"
         )
 
         self.req_to_token_pool.write(
-            (req.req_pool_idx, slice(prefix_len, prefix_len + len(kv_loc))), kv_loc
+            (
+                req.req_pool_idx,
+                slice(total_prefix_len, total_prefix_len + len(kv_loc)),
+            ),
+            kv_loc,
         )
 
         # Truncate fill_ids to kv_committed_len so cache_unfinished_req only
@@ -1324,7 +1372,7 @@ class DecodePreallocQueue:
         req.prefix_indices = (
             prefix_indices if prefix_len > 0 else torch.empty((0,), dtype=torch.int64)
         )
-        req.set_extend_input_len(len(req.fill_ids) - prefix_len)
+        req.set_extend_input_len(len(req.fill_ids) - total_prefix_len)
 
         # Return the transfer destination indices:
         if self.scheduler.enable_hisparse:
@@ -1332,7 +1380,7 @@ class DecodePreallocQueue:
         return kv_loc
 
 
-class DecodeTransferQueue:
+class DecodeTransferQueue(DecodeHiCacheTransferMixin):
     """
     Store the requests that is polling kv
     """
@@ -1433,7 +1481,9 @@ class DecodeTransferQueue:
             decode_req.kv_receiver = None
             return
 
-        # Success - commit the transfer
+        self._commit_hicache_local_restore_to_req(decode_req)
+
+        # Case 3: Success - commit the transfer
         decode_req.req.output_ids.append(output_id[0].item())
         decode_req.req.cached_tokens = cached_tokens[0].item()
         # The prefill node already reported its prefix-cache hit in
@@ -1475,8 +1525,13 @@ class DecodeTransferQueue:
         return
 
     def _poll_with_metadata_gate(self) -> List[int]:
+        pollers = (
+            [HiCacheRestoreGatedKVReceiver(dr) for dr in self.queue]
+            if self.scheduler.enable_decode_hicache
+            else [dr.kv_receiver for dr in self.queue]
+        )
         return poll_and_all_reduce(
-            [dr.kv_receiver for dr in self.queue],
+            pollers,
             self.gloo_group,
             decode_reqs=self.queue,
             metadata_buffers=self.metadata_buffers,
@@ -1507,6 +1562,15 @@ class DecodeTransferQueue:
         if not self.queue:
             return []
 
+        if self.scheduler.enable_decode_hicache:
+            self._process_hicache_local_restores(
+                [
+                    decode_req
+                    for decode_req in self.queue
+                    if rids_to_check is None or decode_req.req.rid in rids_to_check
+                ]
+            )
+
         if self.enable_staging:
             polls = self._poll_with_staging()
         else:
@@ -1518,12 +1582,21 @@ class DecodeTransferQueue:
             if rids_to_check is not None and decode_req.req.rid not in rids_to_check:
                 continue
 
+            hicache_restore_status = decode_req.hicache_restore_status
+            if (
+                poll == KVPoll.Failed
+                or hicache_restore_status == HiCacheRestoreResult.FAILED
+            ):
+                error_message = (
+                    f"Decode transfer failed for request rank={self.tp_rank} "
+                    f"{decode_req.req.rid=} {decode_req.req.bootstrap_room=}"
+                )
                 if poll == KVPoll.Failed:
-                error_message = f"Decode transfer failed for request rank={self.tp_rank} {decode_req.req.rid=} {decode_req.req.bootstrap_room=}"
                     try:
                         decode_req.kv_receiver.failure_exception()
                     except Exception as e:
                         error_message += f" with exception {e}"
+                self._clean_hicache_prefetch_resources(decode_req)
                 logger.error(error_message)
                 prepare_abort(
                     decode_req.req,
@@ -1543,6 +1616,11 @@ class DecodeTransferQueue:
                     self.scheduler.metrics_collector.increment_transfer_failed_reqs()
                 continue
             elif poll == KVPoll.Success:
+                if (
+                    self.scheduler.enable_decode_hicache
+                    and hicache_restore_status == HiCacheRestoreResult.PENDING
+                ):
+                    continue
                 self._commit_transfer_to_req(decode_req)
                 indices_to_remove.add(i)
                 # Check if request was aborted due to corruption
@@ -1555,6 +1633,7 @@ class DecodeTransferQueue:
                         self.scheduler.hisparse_coordinator.request_finished(
                             decode_req.req
                         )
+                    self._clean_hicache_prefetch_resources(decode_req)
                     release_kv_cache(decode_req.req, self.tree_cache, is_insert=False)
                     if self.scheduler.metrics_reporter.enable_metrics:
                         self.scheduler.metrics_collector.increment_transfer_failed_reqs()
@@ -1730,19 +1809,13 @@ class SchedulerDisaggregationDecodeMixin:
             # we can only add at least `num_not_used_batch` new batch to the running queue
             if i < num_not_used_batch:
                 can_run_list.append(req)
-                # Decode-radix path: do NOT re-match prefix here.
+                # Decode-radix path: new requests already matched in
-                # `pop_preallocated` already took a tree snapshot and used it
+                # `pop_preallocated`. Retracted requests reset `last_node`,
-                # to (1) pre-allocate KV, (2) choose delta pages for transfer,
+                # so re-match only when that state is missing.
-                # and (3) set cache_protected_len/last_node for correct frees.
+                if self.server_args.disaggregation_decode_enable_radix_cache:
-                # Re-matching now can observe a newer tree (other reqs may have
+                    tree_cache = self.tree_cache if req.last_node is None else None
-                # inserted the same prefix) and overwrite cache_protected_len,
+                else:
-                # making `cache_unfinished_req` free the wrong range (leak).
+                    tree_cache = self.tree_cache
-                # Non-radix decode keeps the original behavior.
-                tree_cache = (
-                    None
-                    if self.server_args.disaggregation_decode_enable_radix_cache
-                    else self.tree_cache
-                )
                 req.init_next_round_input(tree_cache)
                 # Truncate fill_ids to kv_committed_len so cache_unfinished_req
                 # only sees committed KV (fill_ids includes one uncommitted token).
@@ -1778,6 +1851,9 @@ class SchedulerDisaggregationDecodeMixin:
         return new_batch
 
     def process_decode_queue(self: Scheduler):
+        if self.enable_decode_hicache:
+            self.tree_cache.check_hicache_events()
+
         if self.server_args.disaggregation_decode_enable_offload_kvcache:
             self.decode_offload_manager.check_offload_progress()
 

python/sglang/srt/disaggregation/decode_hicache_mixin.py

@@ -0,0 +1,311 @@
+"""HiCache integration mixins for the decode side of PD disaggregation"""
+
+from __future__ import annotations
+
+import logging
+from dataclasses import dataclass
+from enum import Enum
+from typing import TYPE_CHECKING, Any, List, Optional
+
+import torch
+
+from sglang.srt.disaggregation.base import KVPoll
+from sglang.srt.managers.schedule_policy import match_prefix_for_req
+from sglang.srt.mem_cache.base_prefix_cache import InitLoadBackParams
+
+if TYPE_CHECKING:
+    from sglang.srt.disaggregation.decode import DecodeRequest
+    from sglang.srt.managers.schedule_batch import Req
+
+logger = logging.getLogger(__name__)
+
+
+@dataclass
+class DecodePrefixMatch:
+    prefix_indices: torch.Tensor
+    l2_host_hit_length: int
+    l3_storage_hit_length: int
+    last_device_node: Any
+    last_host_node: Any = None
+    prefetch_registered: bool = False
+
+    @property
+    def l1_prefix_len(self) -> int:
+        return len(self.prefix_indices)
+
+    @property
+    def decode_prefix_len(self) -> int:
+        return self.l1_prefix_len + self.l2_host_hit_length + self.l3_storage_hit_length
+
+    @property
+    def needs_local_restore(self) -> bool:
+        return self.decode_prefix_len > self.l1_prefix_len
+
+    @property
+    def restore_token_count(self) -> int:
+        """Number of tokens that need L2/L3 load_back to device."""
+        return self.decode_prefix_len - self.l1_prefix_len
+
+
+class HiCacheRestoreResult(Enum):
+    """Outcome of one tick of the HiCache local-restore state machine."""
+
+    PENDING = "pending"
+    READY = "ready"
+    FAILED = "failed"
+
+
+class DecodeHiCachePreallocMixin:
+    """HiCache hooks for ``DecodePreallocQueue``: issue prefetch + reserve tokens."""
+
+    def _build_decode_prefix_match(self, req: "Req", result: Any) -> DecodePrefixMatch:
+        """Convert a ``match_prefix_for_req`` result into ``DecodePrefixMatch``.
+
+        Performs the optional L3 storage hit length query when decode-side
+        HiCache is enabled and the last host node is backed up.
+        """
+        prefix_indices = result.device_indices
+        l1_prefix_len = len(prefix_indices)
+        l2_host_hit_length = result.host_hit_length
+
+        l3_storage_hit_length = 0
+        last_host_node = None
+        if self.scheduler.enable_decode_hicache:
+            last_host_node = result.last_host_node
+            if last_host_node.backuped or last_host_node is self.tree_cache.root_node:
+                matched_len = l1_prefix_len + l2_host_hit_length
+                suffix_tokens = req.origin_input_ids[matched_len:]
+                last_hash = last_host_node.get_last_hash_value()
+                prefix_keys = (
+                    last_host_node.get_prefix_hash_values(last_host_node.parent)
+                    if self.tree_cache.hicache_storage_pass_prefix_keys
+                    else None
+                )
+                l3_storage_hit_length = self.tree_cache.query_storage_hit_length(
+                    last_host_node,
+                    suffix_tokens,
+                    last_hash,
+                    prefix_keys,
+                )
+
+        return DecodePrefixMatch(
+            prefix_indices=prefix_indices,
+            l2_host_hit_length=l2_host_hit_length,
+            l3_storage_hit_length=l3_storage_hit_length,
+            last_device_node=result.last_device_node,
+            last_host_node=last_host_node if l3_storage_hit_length > 0 else None,
+        )
+
+    def _start_hicache_prefetch(
+        self, req: "Req", prefix_match: Optional["DecodePrefixMatch"]
+    ) -> None:
+        """Issue L3 storage prefetch after admission succeeds.
+
+        On failure, degrades to L2-only restore by clearing l3 fields.
+        """
+        if (
+            prefix_match is None
+            or prefix_match.l3_storage_hit_length <= 0
+            or prefix_match.last_host_node is None
+        ):
+            return
+        try:
+            node = prefix_match.last_host_node
+            matched_len = prefix_match.l1_prefix_len + prefix_match.l2_host_hit_length
+            suffix = req.origin_input_ids[
+                matched_len : matched_len + prefix_match.l3_storage_hit_length
+            ]
+            last_hash = node.get_last_hash_value()
+            prefix_keys = (
+                node.get_prefix_hash_values(node.parent)
+                if self.tree_cache.hicache_storage_pass_prefix_keys
+                else None
+            )
+            self.tree_cache.prefetch_from_storage(
+                req.rid, node, suffix, last_hash, prefix_keys
+            )
+            prefix_match.prefetch_registered = (
+                req.rid in self.tree_cache.ongoing_prefetch
+            )
+        except Exception as e:
+            logger.warning(
+                "HiCache L3 prefetch failed for rid=%s: %s; falling back to L2-only LoadingBack",
+                req.rid,
+                e,
+            )
+            prefix_match.l3_storage_hit_length = 0
+            prefix_match.prefetch_registered = False
+
+    def _hicache_pending_restore_tokens(self) -> int:
+        """Total device tokens reserved for pending HiCache L2/L3 load_back."""
+        if not self.scheduler.enable_decode_hicache:
+            return 0
+        return sum(
+            dr.prefix_match.restore_token_count
+            for dr in self.transfer_queue.queue
+            if dr.prefix_match is not None
+            and dr.hicache_restore_status == HiCacheRestoreResult.PENDING
+            and dr.hicache_restored_node is None
+        )
+
+
+class HiCacheRestoreGatedKVReceiver:
+    """Wraps a kv_receiver so KVPoll.Success is gated on HiCache restore READY."""
+
+    def __init__(self, decode_req: "DecodeRequest"):
+        self.decode_req = decode_req
+
+    def poll(self) -> KVPoll:
+        poll = self.decode_req.kv_receiver.poll()
+        if (
+            poll == KVPoll.Success
+            and self.decode_req.hicache_restore_status == HiCacheRestoreResult.PENDING
+        ):
+            return KVPoll.Transferring
+        return poll
+
+
+class DecodeHiCacheTransferMixin:
+    """HiCache hooks for ``DecodeTransferQueue``: drive restore state machine."""
+
+    def _clean_hicache_prefetch_resources(self, decode_req: "DecodeRequest") -> None:
+        if (
+            decode_req.prefix_match is not None
+            and decode_req.prefix_match.prefetch_registered
+        ):
+            self.tree_cache.release_aborted_request(decode_req.req.rid)
+        if decode_req.hicache_restored_node is not None:
+            self.tree_cache.dec_lock_ref(decode_req.hicache_restored_node)
+            decode_req.hicache_restored_node = None
+
+    def _try_hicache_queue_load_back(self, dr: "DecodeRequest") -> bool:
+        """Queue one L2->L1 load_back op for ``dr``; True iff a DMA was queued.
+
+        On success, ``dr.hicache_restored_node`` and ``hicache_restored_kv_indices``
+        are populated, and an inc_lock_ref is held until commit/abort.
+        Trivial cases (all-on-device / no needed coverage) auto-flip to READY.
+        Failback paths flip to FAILED.
+        """
+        pm = dr.prefix_match
+
+        # Wait for L3 -> L2 prefetch to drain (skip when no L3 hit).
+        if pm.l3_storage_hit_length > 0:
+            if not self.tree_cache.check_prefetch_progress(dr.req.rid):
+                return False
+            self.tree_cache.pop_prefetch_loaded_tokens(dr.req.rid)
+
+        # Re-match: req.last_node / prefix_indices updated to current device state.
+        rematch = match_prefix_for_req(
+            self.tree_cache,
+            dr.req,
+            dr.req.origin_input_ids,
+            cow_mamba=False,
+            include_req=True,
+        )
+        new_indices, restored_node = self.tree_cache.init_load_back(
+            InitLoadBackParams(
+                best_match_node=rematch.best_match_node,
+                host_hit_length=rematch.host_hit_length,
+                req=dr.req,
+            )
+        )
+        # Failback: total coverage < required prefix means device alloc likely failed.
+        if len(rematch.device_indices) + len(new_indices) < pm.decode_prefix_len:
+            logger.warning(
+                "HiCache load_back failed for rid=%s: device_indices=%d, "
+                "new_indices=%d, expected decode_prefix_len=%d (l1=%d, l2=%d, l3=%d)",
+                dr.req.rid,
+                len(rematch.device_indices),
+                len(new_indices),
+                pm.decode_prefix_len,
+                pm.l1_prefix_len,
+                pm.l2_host_hit_length,
+                pm.l3_storage_hit_length,
+            )
+            dr.hicache_restore_status = HiCacheRestoreResult.FAILED
+            return False
+
+        dr.hicache_restored_kv_indices = torch.cat(
+            [rematch.device_indices[pm.l1_prefix_len :], new_indices]
+        )
+        dr.hicache_restored_node = restored_node
+        self.tree_cache.inc_lock_ref(restored_node)
+
+        if len(new_indices) == 0:
+            # Whole prefix already on device; no DMA needed.
+            dr.hicache_restore_status = HiCacheRestoreResult.READY
+            return False
+        return True
+
+    def _process_hicache_local_restores(
+        self, decode_reqs: List["DecodeRequest"]
+    ) -> None:
+        if not hasattr(self.tree_cache, "is_load_back_event_done"):
+            return
+
+        # Filter once: keep only PENDING reqs that still need restore work;
+        # trivially-done reqs (no prefix_match / nothing to restore) flip to READY.
+        active: List["DecodeRequest"] = []
+        for dr in decode_reqs:
+            if dr.hicache_restore_status != HiCacheRestoreResult.PENDING:
+                continue
+            pm = dr.prefix_match
+            if pm is None or not pm.needs_local_restore:
+                dr.hicache_restore_status = HiCacheRestoreResult.READY
+                continue
+            active.append(dr)
+
+        # Phase A: advance in-flight DMAs to READY.
+        for dr in active:
+            if (
+                dr.hicache_restored_node is not None
+                and self.tree_cache.is_load_back_event_done(
+                    dr.hicache_load_consumer_index
+                )
+            ):
+                dr.hicache_restore_status = HiCacheRestoreResult.READY
+
+        # Phase B: queue new load_back ops if the next slot is free.
+        # The (producer_index + 1) check ensures we never overwrite a still-in-flight slot:
+        # if a previous req holds that slot and isn't done, its event won't be signaled.
+        counter = self.tree_cache.cache_controller.layer_done_counter
+        if not self.tree_cache.is_load_back_event_done(
+            (counter.producer_index + 1) % counter.num_counters
+        ):
+            return
+        queued = [
+            dr
+            for dr in active
+            if dr.hicache_restored_node is None
+            and self._try_hicache_queue_load_back(dr)
+        ]
+        if not queued:
+            return
+
+        # Phase C: kick off merged DMA, bind consumer_index for Phase A polling next tick.
+        consumer_index = self.tree_cache.ready_to_load_host_cache()
+        if consumer_index < 0:
+            for dr in queued:
+                dr.hicache_restore_status = HiCacheRestoreResult.READY
+            return
+        for dr in queued:
+            dr.hicache_load_consumer_index = consumer_index
+
+    def _commit_hicache_local_restore_to_req(self, decode_req: "DecodeRequest") -> None:
+        prefix_match = decode_req.prefix_match
+        if prefix_match is None or not prefix_match.needs_local_restore:
+            return
+
+        self.tree_cache.dec_lock_ref(prefix_match.last_device_node)
+
+        self.tree_cache.req_to_token_pool.write(
+            (
+                decode_req.req.req_pool_idx,
+                slice(prefix_match.l1_prefix_len, prefix_match.decode_prefix_len),
+            ),
+            decode_req.hicache_restored_kv_indices,
+        )
+        decode_req.req.prefix_indices = torch.cat(
+            [prefix_match.prefix_indices, decode_req.hicache_restored_kv_indices]
+        )
+        decode_req.req.last_node = decode_req.hicache_restored_node

python/sglang/srt/managers/scheduler.py

@@ -339,6 +339,10 @@ class Scheduler(
         self.page_size = server_args.page_size
         self.enable_hierarchical_cache = server_args.enable_hierarchical_cache
         self.enable_hicache_storage = server_args.hicache_storage_backend is not None
+        self.enable_decode_hicache = (
+            server_args.disaggregation_decode_enable_radix_cache
+            and self.enable_hierarchical_cache
+        )
         self.max_recv_per_poll = envs.SGLANG_SCHEDULER_MAX_RECV_PER_POLL.get()
         self.enable_hisparse = server_args.enable_hisparse
         self.hisparse_coordinator: Optional[HiSparseCoordinator] = None

python/sglang/srt/mem_cache/hiradix_cache.py

@@ -852,6 +852,20 @@ class HiRadixCache(RadixCache):
         # ACK until all events are processed
         del self.cache_controller.ack_load_queue[:finish_count]
 
+    def is_load_back_event_done(self, consumer_index: int) -> bool:
+        """Return True after the local load-back event is complete."""
+        if consumer_index < 0:
+            return True
+
+        finish_event = self.cache_controller.layer_done_counter.events[
+            consumer_index
+        ].finish_event
+        if not finish_event.query():
+            return False
+
+        self.loading_check()
+        return True
+
     def evictable_size(self):
         return self.evictable_size_
 
@@ -1110,6 +1124,42 @@ class HiRadixCache(RadixCache):
             last_node,
         )
 
+    def query_storage_hit_length(
+        self,
+        last_host_node: TreeNode,
+        new_input_tokens: List[int],
+        last_hash: Optional[str] = None,
+        prefix_keys: Optional[List[str]] = None,
+    ) -> int:
+        if not self.enable_storage or self.cache_controller.prefetch_rate_limited():
+            return 0
+
+        prefetch_key = RadixKey(
+            new_input_tokens,
+            extra_key=last_host_node.key.extra_key,
+            is_bigram=self.is_eagle,
+        ).page_aligned(self.page_size)
+        if len(prefetch_key) < self.prefetch_threshold:
+            return 0
+
+        operation = PrefetchOperation(
+            "__storage_hit_query__",
+            self.cache_controller.mem_pool_host.get_dummy_flat_data_page()[:0],
+            prefetch_key,
+            last_hash,
+            prefix_keys,
+        )
+        hash_values, storage_hit_count = self.cache_controller._storage_hit_query(
+            operation
+        )
+        storage_hit_count_tensor = torch.tensor(storage_hit_count, dtype=torch.int)
+        self._all_reduce_attn_groups(
+            storage_hit_count_tensor, torch.distributed.ReduceOp.MIN
+        )
+        storage_hit_count = storage_hit_count_tensor.item()
+        storage_hit_count = storage_hit_count - (storage_hit_count % self.page_size)
+        return storage_hit_count
+
     def ready_to_load_host_cache(self) -> int:
         """
         Notify the cache controller to start the KV cache loading.

test/registered/disaggregation/test_disaggregation_decode_radix_cache.py

@@ -1,11 +1,21 @@
+import asyncio
+import os
+import shutil
+import tempfile
 import time
 import unittest
 from types import SimpleNamespace
 
 import requests
 
+from sglang.benchmark.datasets.random import sample_random_requests
+from sglang.benchmark.utils import get_tokenizer
 from sglang.test.ci.ci_register import register_cuda_ci
-from sglang.test.kits.cache_hit_kit import run_multiturn_cache_hit_test
+from sglang.test.kits.cache_hit_kit import (
+    async_request_sglang_generate,
+    gen_payload,
+    run_multiturn_cache_hit_test,
+)
 from sglang.test.run_eval import run_eval
 from sglang.test.server_fixtures.disaggregation_fixture import (
     PDDisaggregationServerBase,
@@ -140,5 +150,120 @@ class TestDisaggregationDecodeRadixCacheMooncake(
     transfer_backend_name = "mooncake"
 
 
+@unittest.skipUnless(
+    is_in_ci() or _has_mooncake(),
+    "Mooncake is required for decode radix cache disaggregation coverage.",
+)
+class TestDisaggregationDecodeRadixHiCacheFileBackend(PDDisaggregationServerBase):
+    extra_prefill_args = [
+        "--enable-hierarchical-cache",
+        "--hicache-ratio",
+        "1.2",
+        "--hicache-write-policy",
+        "write_through",
+        "--hicache-storage-backend",
+        "file",
+        "--hicache-storage-prefetch-policy",
+        "wait_complete",
+        "--hicache-io-backend",
+        "kernel",
+        "--hicache-mem-layout",
+        "page_first",
+        "--page-size",
+        "64",
+    ]
+    extra_decode_args = [
+        "--disaggregation-decode-enable-radix-cache",
+        *extra_prefill_args,
+    ]
+    transfer_backend_name = "mooncake"
+
+    @classmethod
+    def setUpClass(cls):
+        cls.hicache_dir = tempfile.mkdtemp(prefix="sglang-hicache-")
+        os.environ["SGLANG_HICACHE_FILE_BACKEND_STORAGE_DIR"] = cls.hicache_dir
+
+        super().setUpClass()
+        cls.model = try_cached_model(DEFAULT_MODEL_NAME_FOR_TEST)
+        cls.transfer_backend = [
+            "--disaggregation-transfer-backend",
+            cls.transfer_backend_name,
+        ]
+        cls.launch_all()
+
+    @classmethod
+    def tearDownClass(cls):
+        super().tearDownClass()
+        os.environ.pop("SGLANG_HICACHE_FILE_BACKEND_STORAGE_DIR", None)
+        shutil.rmtree(cls.hicache_dir, ignore_errors=True)
+
+    def _post_ok(self, url):
+        response = requests.post(url, timeout=60)
+        response.raise_for_status()
+
+    def _flush_memory_cache(self):
+        self._post_ok(f"{self.prefill_url}/flush_cache?timeout=30")
+        self._post_ok(f"{self.decode_url}/flush_cache?timeout=30")
+
+    def _generate(self, input_ids, output_len):
+        output = asyncio.run(
+            async_request_sglang_generate(
+                gen_payload(input_ids, output_len),
+                f"{self.base_url}/generate",
+            )
+        )
+        self.assertTrue(output.success, output.error)
+        return output
+
+    def _sample_token_ids(self, input_len, output_len, num_prompts=1):
+        tokenizer = get_tokenizer(self.model)
+        return [
+            list(request.prompt)
+            for request in sample_random_requests(
+                input_len=input_len,
+                output_len=output_len,
+                num_prompts=num_prompts,
+                range_ratio=1.0,
+                tokenizer=tokenizer,
+                dataset_path="",
+                return_text=False,
+            )
+        ]
+
+    def test_decode_hicache_file_backend_l3_reuses_decode_output_after_flush(self):
+        self._post_ok(f"{self.decode_url}/hicache/storage-backend/clear")
+        self._flush_memory_cache()
+
+        num_rounds = 5
+        output_len = 64
+        history = self._sample_token_ids(
+            input_len=256, output_len=output_len, num_prompts=1
+        )[0]
+        suffixes = self._sample_token_ids(
+            input_len=64, output_len=output_len, num_prompts=num_rounds - 1
+        )
+
+        prev_prompt_len = 0
+        prev_output_len = 0
+        for round_idx in range(num_rounds):
+            output = self._generate(history, output_len)
+            if round_idx == 0:
+                self.assertEqual(output.cached_tokens, 0)
+            else:
+                self.assertGreaterEqual(
+                    output.cached_tokens,
+                    prev_prompt_len + prev_output_len,
+                )
+
+            history.extend(output.output_ids)
+            prev_prompt_len = output.prompt_len
+            prev_output_len = len(output.output_ids)
+
+            if round_idx < num_rounds - 1:
+                history.extend(suffixes[round_idx])
+                time.sleep(1)
+                self._flush_memory_cache()
+
+
 if __name__ == "__main__":
     unittest.main()

test/registered/unit/managers/test_priority_scheduling_disaggregation.py

@@ -106,11 +106,13 @@ class TestDecodePreallocQueuePriority(unittest.TestCase):
         queue._resolve_pending_reqs = MagicMock()
         queue._update_handshake_waiters = MagicMock()
         queue._allocatable_tokens = MagicMock(return_value=1000)
-        queue._pre_alloc = MagicMock(
+
-            side_effect=lambda req, prefix_indices=None, prefix_len=0: torch.arange(
+        def pre_alloc_mock(req, prefix_indices=None, prefix_len=0, total_prefix_len=0):
+            return torch.arange(
                 len(req.origin_input_ids) - prefix_len, dtype=torch.int64
             )
-        )
+
+        queue._pre_alloc = MagicMock(side_effect=pre_alloc_mock)
 
         queue.req_to_token_pool = MagicMock()
         queue.req_to_token_pool.available_size.return_value = 100

test/registered/unit/mem_cache/test_decode_radix_lock_ref.py

@@ -32,6 +32,7 @@ from unittest.mock import MagicMock
 import torch
 
 from sglang.srt.disaggregation.decode import DecodePreallocQueue
+from sglang.srt.disaggregation.decode_hicache_mixin import DecodePrefixMatch
 from sglang.srt.mem_cache.base_prefix_cache import (
     InsertParams,
     MatchPrefixParams,
@@ -312,7 +313,12 @@ class TestDecodeLockRefScenarios(unittest.TestCase):
         queue._resolve_pending_reqs = MagicMock()
         queue._update_handshake_waiters = MagicMock()
         queue._match_prefix_and_lock = MagicMock(
-            return_value=(torch.arange(4, dtype=torch.int64), 4)
+            return_value=DecodePrefixMatch(
+                prefix_indices=torch.arange(4, dtype=torch.int64),
+                l2_host_hit_length=0,
+                l3_storage_hit_length=0,
+                last_device_node=req.last_node,
+            )
         )
         queue._pre_alloc = MagicMock(
             side_effect=AssertionError("_pre_alloc should not run")