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[https://nvbugs/5480289][fix] release slot manager in mtp MTPHiddenStatesManager by yweng0828 · Pull Request #7340 · NVIDIA/TensorRT-LLM · GitHub
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@yweng0828 yweng0828 commented Aug 28, 2025

Summary by CodeRabbit

  • Bug Fixes
    • Improved shutdown reliability by ensuring all resources and slots are fully released, reducing memory leaks and stuck allocations.
    • Enabled cascading cleanup so dependent components correctly tear down in order, improving stability during shutdown.
    • Clearing GPU execution state now removes stale padding references to prevent unintended reuse.
    • Overall, teardown is more predictable and robust, minimizing residual state between runs and lowering the chance of OOMs or hangs after repeated starts/stops.

Description

The root cause of this issue is that we didn't release the dummy request and the occupied slot after the KV cache estimation. This caused the number of slots required to exceed max_num_requests during the CUDA graph warmup.

Fix Step 1: After completing the KV cache estimation, we need to release the resources occupied by the model_engine and the dummy requests.
Fix Step 2: Implement the shutdown() function of the MTP's MTPHiddenStatesManager. We need to properly release the slot (which is used by the dummy request) in the slot manager during _release_cuda_graphs().

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@yweng0828 yweng0828 requested review from a team as code owners August 28, 2025 09:45
@yweng0828 yweng0828 requested a review from kris1025 August 28, 2025 09:45
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coderabbitai bot commented Aug 28, 2025

📝 Walkthrough

Walkthrough

Adds a SlotManager.shutdown() method to forcibly release all slots, wires MTPHiddenStatesManager.shutdown() to call it, and updates CUDAGraphRunner.clear() to also reset padding_dummy_request to None.

Changes

Cohort / File(s) Summary
Resource teardown API
tensorrt_llm/_torch/pyexecutor/resource_manager.py
Introduces SlotManager.shutdown() to iterate over active request-slot mappings, call remove_slot for each, and assert all slots are freed.
Speculative MTP shutdown hook
tensorrt_llm/_torch/speculative/mtp.py
Changes MTPHiddenStatesManager.shutdown() to invoke SlotManager.shutdown() for proper cleanup.
CUDA graph runner state clear
tensorrt_llm/_torch/pyexecutor/cuda_graph_runner.py
Extends clear() to also set self.padding_dummy_request = None during state reset.

Sequence Diagram(s)

sequenceDiagram
  autonumber
  actor Client
  participant MTPHiddenStatesManager as MTPHiddenStatesManager
  participant SlotManager as SlotManager
  participant Slots as Slots (internal)

  Client->>MTPHiddenStatesManager: shutdown()
  MTPHiddenStatesManager->>SlotManager: shutdown()
  rect rgb(235, 245, 255)
    note right of SlotManager: Iterate current request→slot map
    loop For each active slot
      SlotManager->>Slots: remove_slot(request_id)
      Slots-->>SlotManager: slot freed
    end
  end
  SlotManager-->>MTPHiddenStatesManager: all slots released (asserts pass)
  MTPHiddenStatesManager-->>Client: shutdown complete
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Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

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Actionable comments posted: 1

🧹 Nitpick comments (6)
tensorrt_llm/_torch/pyexecutor/cuda_graph_runner.py (2)

49-50: Fix type annotation: use LlmRequest, not an undefined "Request".

“Request” isn’t defined/imported; use LlmRequest under TYPE_CHECKING to satisfy static checkers.

 if TYPE_CHECKING:
-    from .model_engine import PyTorchModelEngine
+    from .model_engine import PyTorchModelEngine
+    from .llm_request import LlmRequest
@@
-        self.padding_dummy_request: Optional["Request"] = None
+        self.padding_dummy_request: Optional["LlmRequest"] = None

You can run mypy/pyright locally to ensure no remaining annotation issues.

Also applies to: 14-16


1-1: Add 2025 NVIDIA copyright header.

Required by the repo’s coding guidelines.

+# Copyright (c) 2025, NVIDIA CORPORATION. All rights reserved.
tensorrt_llm/_torch/speculative/mtp.py (2)

88-88: Release MTP GPU pools too, and document shutdown.

Good to shut down the SlotManager. Also drop large CUDA tensors to free memory deterministically on shutdown.

 def shutdown(self):
-        self.slot_manager.shutdown()
+        """Release all MTP resources (slots and GPU pools)."""
+        self.slot_manager.shutdown()
+        # Drop large buffers to free device memory promptly
+        self.mtp_past_hidden_states_pool = None
+        self.mtp_past_tokens_pool = None
+        if self.use_relaxed_acceptance_for_thinking:
+            self.mtp_relaxed_delta_pool = None

1-1: Add 2025 NVIDIA copyright header.

+# Copyright (c) 2025, NVIDIA CORPORATION. All rights reserved.
tensorrt_llm/_torch/pyexecutor/resource_manager.py (2)

981-987: Add a docstring and log invariant failures rather than assert in prod.

Asserts may be stripped in optimized runs; prefer a clear exception or logging.

-    def shutdown(self):
-        req_ids_list = list(self.slot_mapping.keys())
-        for rid in req_ids_list:
-            self.remove_slot(rid)
-        assert len(self.slot_mapping) == 0 and len(
-            self.free_slots) == self.max_num_requests
+    def shutdown(self):
+        """Force-release all active slots and reset to the initial state."""
+        req_ids_list = list(self.slot_mapping.keys())
+        for rid in req_ids_list:
+            self.remove_slot(rid)
+        ok = (len(self.slot_mapping) == 0
+              and len(self.free_slots) == self.max_num_requests)
+        if not ok:
+            raise RuntimeError(
+                f"SlotManager shutdown invariant failed: "
+                f"slot_mapping={len(self.slot_mapping)}, "
+                f"free_slots={len(self.free_slots)}/{self.max_num_requests}"
+            )

1-1: Add 2025 NVIDIA copyright header.

+# Copyright (c) 2025, NVIDIA CORPORATION. All rights reserved.
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Reviewing files that changed from the base of the PR and between ae89163 and 07ae634.

📒 Files selected for processing (3)
  • tensorrt_llm/_torch/pyexecutor/cuda_graph_runner.py (1 hunks)
  • tensorrt_llm/_torch/pyexecutor/resource_manager.py (1 hunks)
  • tensorrt_llm/_torch/speculative/mtp.py (1 hunks)
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Files:

  • tensorrt_llm/_torch/speculative/mtp.py
  • tensorrt_llm/_torch/pyexecutor/cuda_graph_runner.py
  • tensorrt_llm/_torch/pyexecutor/resource_manager.py
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Prepend NVIDIA copyright header with current year to all source files

Files:

  • tensorrt_llm/_torch/speculative/mtp.py
  • tensorrt_llm/_torch/pyexecutor/cuda_graph_runner.py
  • tensorrt_llm/_torch/pyexecutor/resource_manager.py
🧬 Code graph analysis (2)
tensorrt_llm/_torch/speculative/mtp.py (2)
tensorrt_llm/_torch/pyexecutor/resource_manager.py (4)
  • shutdown (80-81)
  • shutdown (355-356)
  • shutdown (981-986)
  • shutdown (1132-1133)
tensorrt_llm/_torch/pyexecutor/py_executor.py (1)
  • shutdown (353-366)
tensorrt_llm/_torch/pyexecutor/resource_manager.py (2)
tensorrt_llm/_torch/speculative/mtp.py (1)
  • shutdown (87-88)
tensorrt_llm/_torch/pyexecutor/py_executor.py (1)
  • shutdown (353-366)
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🔇 Additional comments (1)
tensorrt_llm/_torch/pyexecutor/resource_manager.py (1)

981-987: LGTM: Idempotent bulk release for SlotManager.

Iterating over a snapshot of keys and asserting invariants is correct and safe.

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LGTM

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PR_Github #16868 [ run ] triggered by Bot

@yweng0828 yweng0828 changed the title [https://nvbugs/5480289][fix]release slot manager in mtp MTPHiddenStatesManager [https://nvbugs/5480289][fix] release slot manager in mtp MTPHiddenStatesManager Aug 28, 2025
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PR_Github #16868 [ run ] completed with state SUCCESS
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@yweng0828 yweng0828 force-pushed the yweng/fix_release_slot_manager_in_mtp branch from 07ae634 to ab6cc5b Compare August 29, 2025 08:28
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Signed-off-by: Yue Weng <25103990+yweng0828@users.noreply.github.com>
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@QiJune QiJune merged commit 9a4f606 into NVIDIA:main Sep 3, 2025
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