[Fix] Land the decode mamba checkpoint depth on the tree page under DCP (#35412)

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
Co-authored-by: Ke Bao <ispobaoke@gmail.com>

python/sglang/srt/managers/schedule_batch.py

@@ -4,7 +4,6 @@ from sglang.srt.dllm.config import DllmConfig
 from sglang.srt.model_executor.forward_batch_info import ForwardBatch
 from sglang.srt.runtime_context import (
     get_disagg,
-    get_exec,
     get_schedule,
     get_serving,
     get_spec,
@@ -12,6 +11,7 @@ from sglang.srt.runtime_context import (
     mamba_checkpoint_grid,
     mamba_extra_buffer_enabled,
     mamba_extra_buffer_lazy_enabled,
+    mamba_track_grid,
 )
 from sglang.srt.utils.common import (
     Range,
@@ -3107,7 +3107,7 @@ class ScheduleBatch(ScheduleBatchDisaggregationDecodeMixin):
             )
 
         if mamba_extra_buffer_enabled():
-            mamba_track_interval = get_exec().mamba.mamba_track_interval
+            mamba_track_interval = mamba_track_grid(self.tree_cache.page_size)
 
             if len(self.reqs) == 0:
                 self.mamba_track_indices = torch.empty(

python/sglang/srt/managers/scheduler_components/batch_result_processor.py

@@ -34,10 +34,10 @@ from sglang.srt.model_executor.forward_batch_info import (
 )
 from sglang.srt.runtime_context import (
     get_disagg,
-    get_exec,
     get_memory,
     get_observability,
     mamba_extra_buffer_lazy_enabled,
+    mamba_track_grid,
     max_speculative_num_draft_tokens,
 )
 from sglang.srt.speculative.base_spec_worker import BaseSpecWorker
@@ -1131,7 +1131,7 @@ class SchedulerBatchResultProcessor:
         if known_boundary:
             self._mamba_assert_committed_len_lookahead(req)
             track_seqlen = req.kv_committed_len
-            assert track_seqlen % get_exec().mamba.mamba_track_interval == 0
+            assert track_seqlen % mamba_track_grid(self.tree_cache.page_size) == 0
             at_boundary = True
         else:
             at_boundary, track_seqlen = self._mamba_check_track_boundary(
@@ -1191,7 +1191,7 @@ class SchedulerBatchResultProcessor:
                 other_idx
             ].item() == -1 and mamba_lazy_spec_in_window(
                 req,
-                get_exec().mamba.mamba_track_interval,
+                mamba_track_grid(self.tree_cache.page_size),
                 max_speculative_num_draft_tokens(),
             )
             if (
@@ -1244,7 +1244,7 @@ class SchedulerBatchResultProcessor:
         For spec decode, the boundary is detected by comparing the
         accepted seq_len range against interval boundaries.
         """
-        interval = get_exec().mamba.mamba_track_interval
+        interval = mamba_track_grid(self.tree_cache.page_size)
 
         if batch.spec_algorithm.is_none():
             lookahead = req.decode_batch_idx - batch.mamba_decode_batch_idx_cpu[i]

python/sglang/srt/runtime_context.py

@@ -1490,6 +1490,14 @@ def mamba_checkpoint_grid(tree_page: int) -> int:
     return math.lcm(mamba_cache_chunk_size(), tree_page)
 
 
+def mamba_track_grid(tree_page: int) -> int:
+    """The same granularity for a decode-donated checkpoint, which additionally
+    has to land on the requested ``mamba_track_interval``."""
+    return math.lcm(
+        mamba_checkpoint_grid(tree_page), get_exec().mamba.mamba_track_interval
+    )
+
+
 def max_speculative_num_draft_tokens() -> int | None:
     """The largest draft-token count speculative decoding may use.
 

python/sglang/srt/speculative/dflash_worker_v2.py

@@ -32,7 +32,7 @@ from sglang.srt.model_executor.forward_batch_info import (
     ForwardMode,
     compute_position,
 )
-from sglang.srt.runtime_context import get_exec, get_schedule
+from sglang.srt.runtime_context import get_exec, get_schedule, mamba_track_grid
 from sglang.srt.server_args import ServerArgs
 from sglang.srt.speculative.base_spec_worker import BaseSpecWorker
 from sglang.srt.speculative.dflash_info import DFlashVerifyInput
@@ -1526,7 +1526,7 @@ class DFlashWorkerV2(BaseSpecWorker):
         mamba_steps_to_track = None
 
         if batch.mamba_track_indices is not None:
-            mamba_track_interval = get_exec().mamba.mamba_track_interval
+            mamba_track_interval = mamba_track_grid(batch.tree_cache.page_size)
             to_track_mask = (
                 seq_lens_pre_verify // mamba_track_interval
                 != batch.seq_lens // mamba_track_interval

python/sglang/srt/speculative/dspark_components/dspark_worker_v2.py

@@ -19,7 +19,13 @@ from sglang.srt.model_executor.forward_batch_info import (
     CaptureHiddenMode,
     compute_position,
 )
-from sglang.srt.runtime_context import get_exec, get_parallel, get_schedule, get_spec
+from sglang.srt.runtime_context import (
+    get_exec,
+    get_parallel,
+    get_schedule,
+    get_spec,
+    mamba_track_grid,
+)
 from sglang.srt.server_args import ServerArgs
 from sglang.srt.speculative.base_spec_worker import BaseSpecWorker
 from sglang.srt.speculative.dflash_info_v2 import DFlashDraftInputV2
@@ -815,7 +821,7 @@ class DSparkWorkerV2(BaseSpecWorker):
         mamba_steps_to_track = None
 
         if batch.mamba_track_indices is not None:
-            mamba_track_interval = get_exec().mamba.mamba_track_interval
+            mamba_track_interval = mamba_track_grid(batch.tree_cache.page_size)
             to_track_mask = (
                 seq_lens_pre_verify // mamba_track_interval
                 != seq_lens_post_verify // mamba_track_interval

python/sglang/srt/speculative/spec_utils.py

@@ -47,10 +47,10 @@ from sglang.srt.mem_cache.allocation import (
     assign_req_to_token_pool_func as assign_req_to_token_pool_func,
 )
 from sglang.srt.runtime_context import (
-    get_exec,
     get_spec,
     mamba_extra_buffer_enabled,
     mamba_extra_buffer_lazy_enabled,
+    mamba_track_grid,
     max_speculative_num_draft_tokens,
 )
 from sglang.srt.utils import (
@@ -811,7 +811,7 @@ def _verify_commit_step_indices(
         return last_correct_step_indices, None
     seq_lens_pre_verify = batch.seq_lens
     seq_lens_post_verify = batch.seq_lens + accept_lens
-    mamba_track_interval = get_exec().mamba.mamba_track_interval
+    mamba_track_interval = mamba_track_grid(batch.tree_cache.page_size)
     to_track_mask = (
         seq_lens_pre_verify // mamba_track_interval
         != seq_lens_post_verify // mamba_track_interval
@@ -984,7 +984,7 @@ def commit_mamba_states_after_verify(
         mamba_track_indices = batch.mamba_track_indices
         mamba_steps_to_track = None
         if mamba_track_indices is not None:
-            ti = get_exec().mamba.mamba_track_interval
+            ti = mamba_track_grid(batch.tree_cache.page_size)
             seq_pre = batch.seq_lens
             seq_post = batch.seq_lens + accept_lens
             to_track_mask = seq_pre // ti != seq_post // ti
@@ -1036,7 +1036,7 @@ def spec_prepare_for_decode(batch: ScheduleBatch) -> None:
     if mamba_extra_buffer_lazy_enabled():
         # Scheduler phase (outside forward isolation).
         batch.mamba_lazy_spec_prepare(
-            get_exec().mamba.mamba_track_interval,
+            mamba_track_grid(batch.tree_cache.page_size),
             max_speculative_num_draft_tokens(),
         )
     if batch.spec_algorithm.is_dflash_family():

test/registered/unit/managers/test_batch_result_processor_mamba_boundary.py

@@ -17,6 +17,11 @@ from sglang.test.ci.ci_register import register_cpu_ci
 register_cpu_ci(est_time=1, suite="base-a-test-cpu")
 
 
+# The decode checkpoint grid is lcm(mamba_cache_chunk_size, tree page,
+# interval); keeping all three equal leaves it at the interval under test.
+TRACK_INTERVAL = 4
+
+
 def _make_batch() -> tuple[Req, ScheduleBatch]:
     sampling_params = SamplingParams(max_new_tokens=32)
     sampling_params.normalize(None)
@@ -31,6 +36,7 @@ def _make_batch() -> tuple[Req, ScheduleBatch]:
     req.kv_committed_len = 2
 
     batch = ScheduleBatch(reqs=[req])
+    batch.tree_cache = SimpleNamespace(page_size=TRACK_INTERVAL)
     batch.device = "cpu"
     batch.model_config = SimpleNamespace(is_encoder_decoder=False)
     batch.enable_overlap = True
@@ -57,7 +63,7 @@ def _make_processor() -> SchedulerBatchResultProcessor:
         server_args=SimpleNamespace(),
         model_config=SimpleNamespace(think_end_ids=None),
         token_to_kv_pool_allocator=MagicMock(),
-        tree_cache=None,
+        tree_cache=SimpleNamespace(page_size=TRACK_INTERVAL),
         hisparse_coordinator=None,
         req_to_token_pool=None,
         decode_offload_manager=None,
@@ -154,7 +160,8 @@ class TestMambaBoundaryMaskReuse(unittest.TestCase):
                     # defaults.
                     get_context().override_server_args(
                         mamba_radix_cache_strategy="extra_buffer",
-                        mamba_track_interval=4,
+                        mamba_track_interval=TRACK_INTERVAL,
+                        _mamba_cache_chunk_size=TRACK_INTERVAL,
                     ),
                     patch(
                         "sglang.srt.managers.schedule_batch.alloc_for_decode",

test/registered/unit/managers/test_mamba_checkpoint_depth.py

@@ -14,6 +14,7 @@ from unittest.mock import MagicMock
 import torch
 
 from sglang.srt.managers.schedule_batch import Req, ScheduleBatch
+from sglang.srt.runtime_context import get_context, mamba_track_grid
 from sglang.srt.sampling.sampling_params import SamplingParams
 from sglang.srt.server_args import (
     ServerArgs,
@@ -21,7 +22,7 @@ from sglang.srt.server_args import (
 )
 from sglang.test.ci.ci_register import register_cpu_ci
 
-register_cpu_ci(est_time=1, suite="base-a-test-cpu")
+register_cpu_ci(est_time=2, suite="base-a-test-cpu")
 
 CHUNK = 64
 
@@ -70,5 +71,24 @@ class TestMambaCheckpointDepth(unittest.TestCase):
         self.assertEqual(depth, 20416)
 
 
+class TestMambaTrackGrid(unittest.TestCase):
+    def _grid(self, *, interval: int, tree_page: int, chunk: int = CHUNK) -> int:
+        with get_context().override_server_args(
+            mamba_track_interval=interval, _mamba_cache_chunk_size=chunk
+        ):
+            return mamba_track_grid(tree_page)
+
+    def test_widened_tree_page_rounds_the_interval_up(self):
+        self.assertEqual(self._grid(interval=256, tree_page=512), 512)
+
+    def test_interval_already_on_the_tree_page_is_untouched(self):
+        self.assertEqual(self._grid(interval=256, tree_page=256), 256)
+        self.assertEqual(self._grid(interval=256, tree_page=128), 256)
+        self.assertEqual(self._grid(interval=256, tree_page=64), 256)
+
+    def test_grid_stays_on_the_chunk_size(self):
+        self.assertEqual(self._grid(interval=192, tree_page=64, chunk=128) % 128, 0)
+
+
 if __name__ == "__main__":
     unittest.main()

test/registered/unit/spec/test_ngram_mamba_verify_update.py

@@ -198,8 +198,8 @@ class TestNgramMambaVerifyUpdate(CustomTestCase):
             "sglang.srt.speculative.spec_utils.mambaish_config",
             return_value={"some": "config"},
         ), patch(
-            "sglang.srt.speculative.spec_utils.get_exec",
-            return_value=MagicMock(mamba=MagicMock(mamba_track_interval=256)),
+            "sglang.srt.speculative.spec_utils.mamba_track_grid",
+            return_value=256,
         ):
             commit_mamba_states_after_verify(
                 target_worker,