feat(sglang): support decode session cache admission

third_party/sglang/python/sglang/srt/disaggregation/decode.py

@@ -140,9 +140,9 @@ class DecodeReqToTokenPool:
         # Indices of reqs that already have a req_pool_idx and will reuse
         # their existing slot (e.g. chunked prefill continuing across chunks).
         reusing = [i for i, r in enumerate(reqs) if r.req_pool_idx is not None]
-        assert (
-            len(reusing) <= 1
-        ), "only one chunked request may reuse req_pool_idx in a batch"
+        # Keep decode-side allocation behavior aligned with the shared pool:
+        # local append-prefill can legitimately batch multiple resident-session
+        # requests that each reuse their existing req_pool_idx.
         assert all(
             reqs[i].is_chunked > 0 or reqs[i].kv_committed_len > 0 for i in reusing
         ), "reusing request must be chunked or have committed KV"
@@ -657,6 +657,12 @@ class DecodePreallocQueue:
         allocatable_tokens = self._allocatable_tokens(
             retractable_tokens=retractable_tokens, count_retracted=True
         )
+
+        def refresh_allocatable_tokens() -> int:
+            return self._allocatable_tokens(
+                retractable_tokens=retractable_tokens, count_retracted=True
+            )
+
         # First, remove all failed requests from the queue
         for i, decode_req in enumerate(self.queue):
             if rids_to_check is not None and decode_req.req.rid not in rids_to_check:
@@ -679,6 +685,13 @@ class DecodePreallocQueue:
             if not decode_req.waiting_for_input:
                 continue
 
+            if self.req_to_token_pool.available_size() <= 0:
+                self.scheduler.maybe_trim_decode_session_cache(
+                    required_tokens=max(1, self.num_reserved_decode_tokens),
+                    force=True,
+                    max_sessions=1,
+                )
+                allocatable_tokens = refresh_allocatable_tokens()
                 if self.req_to_token_pool.available_size() <= 0:
                     break
 
@@ -692,6 +705,37 @@ class DecodePreallocQueue:
                 origin_input_len + self.num_reserved_decode_tokens
             )
 
+            if (
+                max(
+                    required_tokens_for_request,
+                    origin_input_len
+                    + min(
+                        decode_req.req.sampling_params.max_new_tokens,
+                        CLIP_MAX_NEW_TOKEN,
+                    )
+                    - retractable_tokens,
+                )
+                > allocatable_tokens
+            ):
+                required_tokens = max(
+                    0,
+                    max(
+                        required_tokens_for_request,
+                        origin_input_len
+                        + min(
+                            decode_req.req.sampling_params.max_new_tokens,
+                            CLIP_MAX_NEW_TOKEN,
+                        )
+                        - retractable_tokens,
+                    )
+                    - allocatable_tokens,
+                )
+                if required_tokens > 0:
+                    self.scheduler.maybe_trim_decode_session_cache(
+                        required_tokens=required_tokens,
+                        force=True,
+                    )
+                    allocatable_tokens = refresh_allocatable_tokens()
                 if (
                     max(
                         required_tokens_for_request,
@@ -705,6 +749,12 @@ class DecodePreallocQueue:
                     > allocatable_tokens
                 ):
                     break
+            if required_tokens_for_request > allocatable_tokens:
+                self.scheduler.maybe_trim_decode_session_cache(
+                    required_tokens=required_tokens_for_request - allocatable_tokens,
+                    force=True,
+                )
+                allocatable_tokens = refresh_allocatable_tokens()
                 if required_tokens_for_request > allocatable_tokens:
                     break
 
@@ -1135,6 +1185,27 @@ class DecodeTransferQueue:
 
 class SchedulerDisaggregationDecodeMixin:
 
+    def _merge_last_local_prefill_batch(self: Scheduler):
+        if self.last_batch is None or not self.last_batch.forward_mode.is_extend():
+            return
+
+        chunked_req_to_exclude = set()
+        if self.last_batch.chunked_req is not None:
+            chunked_req_to_exclude.add(self.last_batch.chunked_req)
+
+        last_bs = self.last_batch.batch_size()
+        self.last_batch.filter_batch(
+            chunked_req_to_exclude=list(chunked_req_to_exclude)
+        )
+        if self.last_batch.batch_size() < last_bs:
+            self.running_batch.batch_is_full = False
+
+        if not self.last_batch.is_empty():
+            if self.running_batch.is_empty():
+                self.running_batch = self.last_batch
+            else:
+                self.running_batch.merge_batch(self.last_batch)
+
     @torch.no_grad()
     def event_loop_normal_disagg_decode(self: Scheduler):
         """A normal scheduler loop for decode worker in disaggregation mode."""
@@ -1213,6 +1284,8 @@ class SchedulerDisaggregationDecodeMixin:
         self: Scheduler,
     ) -> Optional[ScheduleBatch]:
         """Process prebuilt batch and schedule the next decode batch."""
+        self._merge_last_local_prefill_batch()
+
         # Process pending prebuilt batch: output processing + filter + merge
         new_prebuilt_batch = self.get_new_prebuilt_batch()
         if new_prebuilt_batch:
@@ -1229,6 +1302,13 @@ class SchedulerDisaggregationDecodeMixin:
                 else:
                     self.running_batch.merge_batch(new_prebuilt_batch)
 
+        new_local_batch = self.get_new_local_extend_batch()
+        if new_local_batch is not None:
+            ret = self.maybe_prepare_mlp_sync_batch(new_local_batch)
+            if ret:
+                set_schedule_time_batch(ret)
+            return ret
+
         # Schedule decode batch
         if self.running_batch.is_empty():
             ret = None
@@ -1241,6 +1321,22 @@ class SchedulerDisaggregationDecodeMixin:
             set_schedule_time_batch(ret)
         return ret
 
+    def get_new_local_extend_batch(self: Scheduler) -> Optional[ScheduleBatch]:
+        if not self.server_args.disaggregation_decode_allow_local_prefill:
+            return None
+        if len(self.decode_direct_waiting_queue) == 0:
+            return None
+
+        original_waiting_queue = self.waiting_queue
+        try:
+            self.waiting_queue = self.decode_direct_waiting_queue
+            new_batch = self.get_new_batch_prefill()
+            self.decode_direct_waiting_queue = self.waiting_queue
+        finally:
+            self.waiting_queue = original_waiting_queue
+
+        return new_batch
+
     def get_new_prebuilt_batch(self: Scheduler) -> Optional[ScheduleBatch]:
         """Create a schedulebatch for fake completed prefill"""
         if self.grammar_manager.has_waiting_grammars():

third_party/sglang/python/sglang/srt/entrypoints/http_server.py

@@ -124,6 +124,7 @@ from sglang.srt.managers.io_struct import (
     InitWeightsUpdateGroupReqInput,
     LoadLoRAAdapterFromTensorsReqInput,
     LoadLoRAAdapterReqInput,
+    DirectAppendAdmissionReqInput,
     OpenSessionReqInput,
     ParseFunctionCallReq,
     PauseGenerationReqInput,
@@ -1289,6 +1290,11 @@ async def close_session(obj: CloseSessionReqInput, request: Request):
         return _create_error_response(e)
 
 
+@app.post("/session_cache/admit_direct_append")
+async def admit_direct_append(obj: DirectAppendAdmissionReqInput):
+    return await _global_state.tokenizer_manager.admit_direct_append(obj)
+
+
 @app.api_route("/configure_logging", methods=["GET", "POST"])
 @auth_level(AuthLevel.ADMIN_OPTIONAL)
 async def configure_logging(obj: ConfigureLoggingReq, request: Request):

third_party/sglang/python/sglang/srt/managers/io_struct.py

@@ -1597,6 +1597,30 @@ class OpenSessionReqOutput(BaseReq):
     success: bool
 
 
+@dataclass
+class DirectAppendAdmissionReqInput(BaseReq):
+    session_id: str
+    uncached_input_tokens: int
+    output_tokens: int
+
+
+@dataclass
+class DirectAppendAdmissionReqOutput(BaseReq):
+    can_admit: bool
+    resident: bool
+    reason: Optional[str] = None
+    required_tokens: int = 0
+    available_tokens_before: int = 0
+    available_tokens_after: int = 0
+    evicted_session_count: int = 0
+    freed_tokens: int = 0
+    token_usage: float = 0.0
+    num_running_reqs: int = 0
+    decode_prealloc_queue_reqs: int = 0
+    decode_transfer_queue_reqs: int = 0
+    decode_retracted_queue_reqs: int = 0
+
+
 @dataclass
 class HealthCheckOutput(BaseReq):
     pass

third_party/sglang/python/sglang/srt/managers/schedule_batch.py

@@ -1566,6 +1566,23 @@ class ScheduleBatch(ScheduleBatchDisaggregationDecodeMixin):
 
         # Init tensors
         reqs = self.reqs
+        for req in reqs:
+            if req.session is None or not req.session.streaming:
+                continue
+            actual_extend_len = max(0, len(req.fill_ids) - len(req.prefix_indices))
+            if req.extend_input_len != actual_extend_len:
+                logger.warning(
+                    "Correcting streaming-session extend_input_len from %d to %d "
+                    "(rid=%s, session_id=%s, fill_len=%d, prefix_len=%d, kv_committed_len=%d)",
+                    req.extend_input_len,
+                    actual_extend_len,
+                    req.rid,
+                    req.session.session_id,
+                    len(req.fill_ids),
+                    len(req.prefix_indices),
+                    req.kv_committed_len,
+                )
+                req.set_extend_input_len(actual_extend_len)
         input_ids = [r.fill_ids[len(r.prefix_indices) :] for r in reqs]
         extend_num_tokens = sum(len(ids) for ids in input_ids)
         seq_lens = [len(r.fill_ids) for r in reqs]

third_party/sglang/python/sglang/srt/managers/scheduler.py

@@ -94,6 +94,8 @@ from sglang.srt.managers.io_struct import (
     ClearHiCacheReqOutput,
     CloseSessionReqInput,
     ContinueGenerationReqInput,
+    DirectAppendAdmissionReqInput,
+    DirectAppendAdmissionReqOutput,
     DestroyWeightsUpdateGroupReqInput,
     DetachHiCacheStorageReqInput,
     DetachHiCacheStorageReqOutput,
@@ -844,6 +846,7 @@ class Scheduler(
 
     def init_running_status(self):
         self.waiting_queue: List[Req] = []
+        self.decode_direct_waiting_queue: List[Req] = []
         # The running decoding batch for continuous batching
         self.running_batch: ScheduleBatch = ScheduleBatch(reqs=[], batch_is_full=False)
         # The current forward batch
@@ -1215,6 +1218,7 @@ class Scheduler(
                 (AbortReq, self.abort_request),
                 (OpenSessionReqInput, self.open_session),
                 (CloseSessionReqInput, self.close_session),
+                (DirectAppendAdmissionReqInput, self.admit_direct_append),
                 (UpdateWeightFromDiskReqInput, self.update_weights_from_disk),
                 (InitWeightsUpdateGroupReqInput, self.init_weights_update_group),
                 (DestroyWeightsUpdateGroupReqInput, self.destroy_weights_update_group),
@@ -1589,6 +1593,7 @@ class Scheduler(
     def process_input_requests(self, recv_reqs: List):
         now = time.monotonic()
         self.session_controller.maybe_reap(now)
+        self.maybe_trim_decode_session_cache()
         for recv_req in recv_reqs:
             # Skip health check when server is busy — ongoing requests already carry health info.
             if is_health_check_generate_req(recv_req) and not self.is_fully_idle(
@@ -1781,6 +1786,10 @@ class Scheduler(
                 # Invalid request for disaggregated mode
                 if (
                     recv_req.bootstrap_room is None
+                    and not (
+                        self.disaggregation_mode == DisaggregationMode.DECODE
+                        and self.server_args.disaggregation_decode_allow_local_prefill
+                    )
                     and self.transfer_backend != TransferBackend.FAKE
                 ):
                     error_msg = (
@@ -1949,6 +1958,12 @@ class Scheduler(
             )
             req.time_stats.set_prefill_bootstrap_queue_entry_time()
         elif self.disaggregation_mode == DisaggregationMode.DECODE:
+            if self._should_allow_local_prefill_on_decode(req):
+                if not self._set_or_validate_priority(req):
+                    return
+                self.decode_direct_waiting_queue.append(req)
+                req.time_stats.set_wait_queue_entry_time()
+                return
             self.disagg_decode_prealloc_queue.add(req, is_retracted=is_retracted)
             if not is_retracted:
                 req.time_stats.set_decode_prealloc_queue_entry_time()
@@ -1957,6 +1972,88 @@ class Scheduler(
         else:
             raise ValueError(f"Invalid {self.disaggregation_mode=}")
 
+    def _should_allow_local_prefill_on_decode(self, req: Req) -> bool:
+        return (
+            self.disaggregation_mode == DisaggregationMode.DECODE
+            and self.server_args.disaggregation_decode_allow_local_prefill
+            and req.bootstrap_room is None
+        )
+
+    def _decode_session_cache_low_watermark_tokens(self) -> int:
+        return min(
+            self.max_total_num_tokens,
+            max(
+                self.server_args.num_reserved_decode_tokens * 16,
+                self.max_total_num_tokens // 12,
+                16384,
+            ),
+        )
+
+    def _decode_session_cache_target_available_tokens(self) -> int:
+        return min(
+            self.max_total_num_tokens,
+            max(
+                self._decode_session_cache_low_watermark_tokens(),
+                self.server_args.num_reserved_decode_tokens * 24,
+                self.max_total_num_tokens // 8,
+                24576,
+            ),
+        )
+
+    def maybe_trim_decode_session_cache(
+        self,
+        required_tokens: int = 0,
+        force: bool = False,
+        max_sessions: Optional[int] = None,
+        exclude_session_ids: Optional[set[str]] = None,
+    ) -> Dict[str, int]:
+        if (
+            self.disaggregation_mode != DisaggregationMode.DECODE
+            or not isinstance(self.tree_cache, SessionAwareCache)
+        ):
+            return {
+                "evicted_session_count": 0,
+                "freed_tokens": 0,
+                "available_tokens_before": 0,
+                "available_tokens_after": 0,
+            }
+
+        available_tokens = self.token_to_kv_pool_allocator.available_size()
+        low_watermark_tokens = self._decode_session_cache_low_watermark_tokens()
+        target_available_tokens = self._decode_session_cache_target_available_tokens()
+        min_available_tokens = max(
+            low_watermark_tokens,
+            available_tokens + max(0, required_tokens),
+        )
+        target_available_tokens = max(
+            target_available_tokens,
+            min_available_tokens,
+        )
+        if not force and available_tokens >= low_watermark_tokens:
+            return {
+                "evicted_session_count": 0,
+                "freed_tokens": 0,
+                "available_tokens_before": int(available_tokens),
+                "available_tokens_after": int(available_tokens),
+            }
+
+        result = self.session_controller.evict_idle_streaming_sessions_lru(
+            required_tokens=required_tokens,
+            min_available_tokens=min_available_tokens,
+            target_available_tokens=target_available_tokens,
+            max_sessions=max_sessions,
+            exclude_session_ids=exclude_session_ids,
+        )
+        if result["evicted_session_count"] > 0:
+            logger.info(
+                "Trimmed decode session cache via LRU. "
+                f"#evicted_sessions: {result['evicted_session_count']}, "
+                f"#freed_tokens: {result['freed_tokens']}, "
+                f"#available_tokens: {result['available_tokens_before']} -> "
+                f"{result['available_tokens_after']}"
+            )
+        return result
+
     def _set_or_validate_priority(self, req: Req) -> bool:
         """Set the default priority value, or abort the request based on the priority scheduling mode."""
         if self.enable_priority_scheduling and req.priority is None:
@@ -2558,8 +2655,19 @@ class Scheduler(
         if self.enable_hierarchical_cache:
             self.tree_cache.flush_write_through_acks()
 
-        # Check if decode out of memory
-        if (kv_full_retract_flag := not batch.check_decode_mem()) or (
+        # Check if decode out of memory. Before retracting active decode work,
+        # let the worker evict idle streaming-session KV held outside the radix tree.
+        kv_full_retract_flag = not batch.check_decode_mem()
+        idle_session_eviction = None
+        if kv_full_retract_flag:
+            idle_session_eviction = self.maybe_trim_decode_session_cache(
+                required_tokens=max(1, self.server_args.num_reserved_decode_tokens),
+                force=True,
+            )
+            if idle_session_eviction["freed_tokens"] > 0:
+                kv_full_retract_flag = not batch.check_decode_mem()
+
+        if kv_full_retract_flag or (
             TEST_RETRACT and self.forward_ct % TEST_RETRACT_INTERVAL == 0
         ):
             old_available_tokens = self.token_to_kv_pool_allocator.available_size()
@@ -2602,6 +2710,13 @@ class Scheduler(
                 msg_details += (
                     f", #new_token_ratio: {old_ratio:.4f} -> {new_token_ratio:.4f}"
                 )
+            if idle_session_eviction is not None:
+                msg_details += (
+                    ", #idle_session_evicted: "
+                    f"{idle_session_eviction['evicted_session_count']}"
+                    ", #idle_tokens_freed: "
+                    f"{idle_session_eviction['freed_tokens']}"
+                )
             logger.warning(msg_prefix + msg_details)
 
             for req in retracted_reqs:
@@ -2916,6 +3031,7 @@ class Scheduler(
 
         # Waiting queues: waiting + bootstrapping + preallocation + kv transfer (decode)
         idle &= len(self.waiting_queue) == 0
+        idle &= len(self.decode_direct_waiting_queue) == 0
 
         if not for_health_check:
             # Grammar queue and prefill inflight queue may not produce batch
@@ -3077,6 +3193,9 @@ class Scheduler(
             "graph": round(self.tp_worker.model_runner.graph_mem_usage, 2),
         }
         ret["effective_max_running_requests_per_dp"] = self.max_running_requests
+        ret["session_cache"] = (
+            self.session_controller.get_streaming_session_cache_status()
+        )
 
         if not self.spec_algorithm.is_none() and self.spec_total_num_forward_ct > 0:
             ret["avg_spec_accept_length"] = (
@@ -3375,6 +3494,86 @@ class Scheduler(
     def close_session(self, recv_req: CloseSessionReqInput):
         self.session_controller.close(recv_req)
 
+    def admit_direct_append(
+        self, recv_req: DirectAppendAdmissionReqInput
+    ) -> DirectAppendAdmissionReqOutput:
+        if (
+            self.disaggregation_mode != DisaggregationMode.DECODE
+            or not self.server_args.disaggregation_decode_allow_local_prefill
+            or not isinstance(self.tree_cache, SessionAwareCache)
+        ):
+            return DirectAppendAdmissionReqOutput(
+                can_admit=False,
+                resident=False,
+                reason="unsupported",
+            )
+
+        session_cache_status = self.session_controller.get_streaming_session_cache_status(
+            recv_req.session_id
+        )
+        target_session = session_cache_status.get("target_session")
+        resident = bool(
+            isinstance(target_session, dict) and target_session.get("resident")
+        )
+        if not resident:
+            return DirectAppendAdmissionReqOutput(
+                can_admit=False,
+                resident=False,
+                reason="session-not-resident",
+                available_tokens_before=int(
+                    self.token_to_kv_pool_allocator.available_size()
+                ),
+                available_tokens_after=int(
+                    self.token_to_kv_pool_allocator.available_size()
+                ),
+                token_usage=(
+                    1.0
+                    - self.token_to_kv_pool_allocator.available_size()
+                    / max(1, self.max_total_num_tokens)
+                ),
+                num_running_reqs=len(self.running_batch.reqs),
+                decode_prealloc_queue_reqs=len(self.disagg_decode_prealloc_queue.queue),
+                decode_transfer_queue_reqs=len(self.disagg_decode_transfer_queue.queue),
+                decode_retracted_queue_reqs=len(
+                    self.disagg_decode_prealloc_queue.retracted_queue
+                ),
+            )
+
+        required_tokens = max(0, recv_req.uncached_input_tokens) + max(
+            0, recv_req.output_tokens
+        )
+        available_tokens_before = int(self.token_to_kv_pool_allocator.available_size())
+        trim_result = self.maybe_trim_decode_session_cache(
+            required_tokens=required_tokens,
+            force=available_tokens_before < required_tokens,
+            exclude_session_ids={recv_req.session_id},
+        )
+        available_tokens_after = int(self.token_to_kv_pool_allocator.available_size())
+        decode_retracted_queue_reqs = len(self.disagg_decode_prealloc_queue.retracted_queue)
+        can_admit = (
+            decode_retracted_queue_reqs == 0
+            and available_tokens_after >= required_tokens
+        )
+        reason = None if can_admit else "no-space"
+
+        return DirectAppendAdmissionReqOutput(
+            can_admit=can_admit,
+            resident=True,
+            reason=reason,
+            required_tokens=int(required_tokens),
+            available_tokens_before=available_tokens_before,
+            available_tokens_after=available_tokens_after,
+            evicted_session_count=int(trim_result["evicted_session_count"]),
+            freed_tokens=int(trim_result["freed_tokens"]),
+            token_usage=(
+                1.0 - available_tokens_after / max(1, self.max_total_num_tokens)
+            ),
+            num_running_reqs=len(self.running_batch.reqs),
+            decode_prealloc_queue_reqs=len(self.disagg_decode_prealloc_queue.queue),
+            decode_transfer_queue_reqs=len(self.disagg_decode_transfer_queue.queue),
+            decode_retracted_queue_reqs=decode_retracted_queue_reqs,
+        )
+
     def maybe_sleep_on_idle(self):
         if self.idle_sleeper is not None:
             self.idle_sleeper.maybe_sleep()

third_party/sglang/python/sglang/srt/managers/session_controller.py

@@ -229,6 +229,12 @@ class Session:
             priority=req.priority,
             routing_key=req.routing_key,
             http_worker_ipc=req.http_worker_ipc,
+            bootstrap_host=req.bootstrap_host,
+            bootstrap_port=req.bootstrap_port,
+            bootstrap_room=req.bootstrap_room,
+            routed_dp_rank=req.routed_dp_rank,
+            disagg_prefill_dp_rank=req.disagg_prefill_dp_rank,
+            extra_key=req.extra_key,
             time_stats=req.time_stats,
         )
         if last_req is not None:
@@ -284,7 +290,7 @@ class SessionController:
         else:
             self._close(session_id)
 
-    def _close(self, session_id: str):
+    def _close(self, session_id: str) -> int:
         session = self.sessions[session_id]
         if session.streaming and session.req_nodes:
             assert len(session.req_nodes) == 1
@@ -303,9 +309,166 @@ class SessionController:
                 mm.release_features()
             node.req.multimodal_inputs = None
 
+        freed_tokens = 0
         if isinstance(self.tree_cache, SessionAwareCache):
-            self.tree_cache.release_session(session_id)
+            freed_tokens = self.tree_cache.release_session(session_id)
         del self.sessions[session_id]
+        return freed_tokens
+
+    def _is_idle_streaming_session(self, session: Session) -> bool:
+        if not session.streaming:
+            return False
+        if not session.req_nodes:
+            return False
+        return all(node.req.finished() for node in session.req_nodes.values())
+
+    def get_streaming_session_cache_status(
+        self, session_id: Optional[str] = None
+    ) -> Dict[str, object]:
+        if not isinstance(self.tree_cache, SessionAwareCache):
+            return {
+                "enabled": False,
+                "eviction_policy": None,
+                "session_count": 0,
+                "resident_session_count": 0,
+                "held_tokens": 0,
+                "available_tokens": 0,
+                "capacity_tokens": 0,
+                "idle_evictable_session_count": 0,
+                "idle_evictable_tokens": 0,
+                "sessions": [],
+                "target_session": None,
+            }
+
+        all_statuses = self.tree_cache.list_session_statuses()
+        session_map = {status["session_id"]: status for status in all_statuses}
+        idle_evictable_tokens = 0
+        idle_evictable_session_count = 0
+        sessions = []
+        for status in all_statuses:
+            session = self.sessions.get(status["session_id"])
+            idle_evictable = session is not None and self._is_idle_streaming_session(
+                session
+            )
+            if idle_evictable and status["resident"]:
+                idle_evictable_session_count += 1
+                idle_evictable_tokens += int(status["resident_tokens"])
+            if session_id is None or status["session_id"] == session_id:
+                sessions.append(
+                    {
+                        **status,
+                        "streaming": bool(session.streaming) if session is not None else True,
+                        "idle_evictable": idle_evictable,
+                        "timed_out": session.is_timed_out() if session is not None else False,
+                    }
+                )
+
+        target_session = session_map.get(session_id) if session_id is not None else None
+        return {
+            "enabled": True,
+            "eviction_policy": "lru",
+            "session_count": len(all_statuses),
+            "resident_session_count": sum(1 for status in all_statuses if status["resident"]),
+            "held_tokens": int(self.tree_cache.session_held_tokens()),
+            "available_tokens": int(self.tree_cache.token_to_kv_pool_allocator.available_size()),
+            "capacity_tokens": int(self.tree_cache.token_to_kv_pool_allocator.size),
+            "idle_evictable_session_count": idle_evictable_session_count,
+            "idle_evictable_tokens": int(idle_evictable_tokens),
+            "sessions": sessions,
+            "target_session": (
+                {
+                    **target_session,
+                    "idle_evictable": (
+                        self._is_idle_streaming_session(self.sessions[target_session["session_id"]])
+                        if target_session is not None
+                        and target_session["session_id"] in self.sessions
+                        else False
+                    ),
+                }
+                if target_session is not None
+                else None
+            ),
+        }
+
+    def evict_idle_streaming_sessions(
+        self,
+        required_tokens: int = 0,
+        max_sessions: Optional[int] = None,
+    ) -> Dict[str, int]:
+        return self.evict_idle_streaming_sessions_lru(
+            required_tokens=required_tokens,
+            max_sessions=max_sessions,
+        )
+
+    def evict_idle_streaming_sessions_lru(
+        self,
+        required_tokens: int = 0,
+        min_available_tokens: int = 0,
+        target_available_tokens: Optional[int] = None,
+        max_sessions: Optional[int] = None,
+        exclude_session_ids: Optional[set[str]] = None,
+    ) -> Dict[str, int]:
+        if not isinstance(self.tree_cache, SessionAwareCache):
+            return {
+                "evicted_session_count": 0,
+                "freed_tokens": 0,
+                "available_tokens_before": 0,
+                "available_tokens_after": 0,
+            }
+
+        available_tokens_before = int(
+            self.tree_cache.token_to_kv_pool_allocator.available_size()
+        )
+        evicted_session_count = 0
+        freed_tokens = 0
+        target_available_tokens = max(
+            int(min_available_tokens),
+            int(target_available_tokens or 0),
+        )
+        candidates = []
+        for status in self.tree_cache.list_session_statuses():
+            if exclude_session_ids and status["session_id"] in exclude_session_ids:
+                continue
+            session = self.sessions.get(status["session_id"])
+            if session is None or not self._is_idle_streaming_session(session):
+                continue
+            if not status["resident"]:
+                continue
+            candidates.append(status)
+
+        for status in candidates:
+            if max_sessions is not None and evicted_session_count >= max_sessions:
+                break
+            available_tokens_now = available_tokens_before + freed_tokens
+            if (
+                required_tokens > 0
+                and freed_tokens >= required_tokens
+                and available_tokens_now >= min_available_tokens
+            ):
+                break
+            if (
+                required_tokens <= 0
+                and min_available_tokens <= 0
+                and target_available_tokens <= 0
+            ):
+                break
+            if (
+                required_tokens <= 0
+                and available_tokens_now >= min_available_tokens
+                and available_tokens_now >= target_available_tokens
+            ):
+                break
+
+            freed = self._close(status["session_id"])
+            evicted_session_count += 1
+            freed_tokens += int(freed)
+
+        return {
+            "evicted_session_count": evicted_session_count,
+            "freed_tokens": freed_tokens,
+            "available_tokens_before": available_tokens_before,
+            "available_tokens_after": available_tokens_before + freed_tokens,
+        }
 
     def maybe_reap(self, now: float, interval: float = 1.0):
         # reap sessions every second

third_party/sglang/python/sglang/srt/managers/tokenizer_communicator_mixin.py

@@ -30,6 +30,8 @@ from sglang.srt.managers.io_struct import (
     ClearHiCacheReqInput,
     ClearHiCacheReqOutput,
     CloseSessionReqInput,
+    DirectAppendAdmissionReqInput,
+    DirectAppendAdmissionReqOutput,
     DestroyWeightsUpdateGroupReqInput,
     DestroyWeightsUpdateGroupReqOutput,
     DetachHiCacheStorageReqInput,
@@ -220,6 +222,9 @@ class TokenizerCommunicatorMixin:
         self.get_internal_state_communicator = _Communicator(
             self.send_to_scheduler, server_args.dp_size
         )
+        self.direct_append_admission_communicator = _Communicator(
+            self.send_to_scheduler, server_args.dp_size
+        )
         self.set_internal_state_communicator = _Communicator(
             self.send_to_scheduler, server_args.dp_size
         )
@@ -316,6 +321,10 @@ class TokenizerCommunicatorMixin:
                     GetInternalStateReqOutput,
                     self.get_internal_state_communicator.handle_recv,
                 ),
+                (
+                    DirectAppendAdmissionReqOutput,
+                    self.direct_append_admission_communicator.handle_recv,
+                ),
                 (
                     SetInternalStateReqOutput,
                     self.set_internal_state_communicator.handle_recv,
@@ -871,6 +880,16 @@ class TokenizerCommunicatorMixin:
         # Many DP ranks
         return [res.internal_state for res in responses]
 
+    async def admit_direct_append(
+        self: TokenizerManager,
+        obj: DirectAppendAdmissionReqInput,
+    ) -> DirectAppendAdmissionReqOutput:
+        self.auto_create_handle_loop()
+        responses: List[DirectAppendAdmissionReqOutput] = (
+            await self.direct_append_admission_communicator(obj)
+        )
+        return responses[0]
+
     async def set_internal_state(
         self: TokenizerManager, obj: SetInternalStateReq
     ) -> List[bool]:

third_party/sglang/python/sglang/srt/mem_cache/session_aware_cache.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import time
 from dataclasses import dataclass, field
 from typing import TYPE_CHECKING, Any, Dict, Optional
 
@@ -57,6 +58,7 @@ class SessionSlot:
     mamba_next_track_idx: Any = None
     mamba_last_track_seqlen: Any = None
     mamba_branching_seqlen: Any = None
+    last_access_time: float = field(default_factory=time.monotonic)
 
     @property
     def is_holding_kv(self) -> bool:
@@ -80,6 +82,7 @@ class SessionSlot:
         self.mamba_next_track_idx = req.mamba_next_track_idx
         self.mamba_last_track_seqlen = req.mamba_last_track_seqlen
         self.mamba_branching_seqlen = req.mamba_branching_seqlen
+        self.last_access_time = time.monotonic()
 
         req.req_pool_idx = None
         req.mamba_pool_idx = None
@@ -97,6 +100,7 @@ class SessionSlot:
         req.mamba_next_track_idx = self.mamba_next_track_idx
         req.mamba_last_track_seqlen = self.mamba_last_track_seqlen
         req.mamba_branching_seqlen = self.mamba_branching_seqlen
+        self.last_access_time = time.monotonic()
 
         # NOTE: req_pool_idx and mamba_pool_idx are intentionally NOT cleared
         # from the slot. During chunked prefill, a request may be rejected by
@@ -247,7 +251,7 @@ class SessionAwareCache(BasePrefixCache):
         """Release all KV resources held by a streaming session."""
         slot = self.slots.pop(session_id, None)
         if slot is None:
-            return
+            return 0
 
         if slot.last_node is not None:
             if slot.swa_uuid_for_lock is not None:
@@ -261,20 +265,58 @@ class SessionAwareCache(BasePrefixCache):
         if slot.is_holding_kv:
             start = slot.cache_protected_len
             end = slot.kv_allocated_len
+            freed_tokens = max(0, end - start)
             if start < end:
                 kv_indices = self.req_to_token_pool.req_to_token[
                     slot.req_pool_idx, start:end
                 ]
                 self.token_to_kv_pool_allocator.free(kv_indices)
             self.req_to_token_pool.free_slots.append(slot.req_pool_idx)
+            return freed_tokens
+        return 0
+
+    def slot_held_tokens(self, slot: SessionSlot) -> int:
+        if not slot.is_holding_kv:
+            return 0
+        allocated = ceil_align(slot.kv_allocated_len, self.page_size)
+        return max(0, allocated - slot.cache_protected_len)
+
+    def get_session_status(self, session_id: str) -> Optional[Dict[str, Any]]:
+        slot = self.slots.get(session_id)
+        if slot is None:
+            return None
+        return {
+            "session_id": session_id,
+            "resident": slot.is_holding_kv,
+            "resident_tokens": int(self.slot_held_tokens(slot)),
+            "kv_committed_len": int(slot.kv_committed_len),
+            "kv_allocated_len": int(slot.kv_allocated_len),
+            "cache_protected_len": int(slot.cache_protected_len),
+            "last_access_time": float(slot.last_access_time),
+        }
+
+    def list_session_statuses(self) -> list[Dict[str, Any]]:
+        statuses = []
+        for session_id, slot in self.slots.items():
+            statuses.append(
+                {
+                    "session_id": session_id,
+                    "resident": slot.is_holding_kv,
+                    "resident_tokens": int(self.slot_held_tokens(slot)),
+                    "kv_committed_len": int(slot.kv_committed_len),
+                    "kv_allocated_len": int(slot.kv_allocated_len),
+                    "cache_protected_len": int(slot.cache_protected_len),
+                    "last_access_time": float(slot.last_access_time),
+                }
+            )
+        statuses.sort(key=lambda item: item["last_access_time"])
+        return statuses
 
     def session_held_tokens(self) -> int:
         """Total KV tokens held by session slots, not tracked by the tree."""
         total = 0
         for slot in self.slots.values():
-            if slot.is_holding_kv:
-                allocated = ceil_align(slot.kv_allocated_len, self.page_size)
-                total += allocated - slot.cache_protected_len
+            total += self.slot_held_tokens(slot)
         return total
 
     def session_held_full_tokens(self) -> int:

third_party/sglang/python/sglang/srt/server_args.py

@@ -697,6 +697,7 @@ class ServerArgs:
     disaggregation_bootstrap_port: int = 8998
     disaggregation_ib_device: Optional[str] = None
     disaggregation_decode_enable_offload_kvcache: bool = False
+    disaggregation_decode_allow_local_prefill: bool = False
     num_reserved_decode_tokens: int = 512  # used for decode kv cache offload in PD
     # FIXME: hack to reduce ITL when decode bs is small
     disaggregation_decode_polling_interval: int = 1
@@ -5772,6 +5773,14 @@ class ServerArgs:
             action="store_true",
             help="Enable async KV cache offloading on decode server (PD mode).",
         )
+        parser.add_argument(
+            "--disaggregation-decode-allow-local-prefill",
+            action="store_true",
+            help=(
+                "Allow decode workers in PD mode to accept direct local requests "
+                "without bootstrap metadata and run local append-prefill."
+            ),
+        )
         parser.add_argument(
             "--num-reserved-decode-tokens",
             type=int,