[https://nvbugs/6525898][fix] Append a constraint of _max_resident_sequences() + reserved-dummy…

[trtllm-agent]

Summary

• Root cause: With avg_seq_len unset no constraints are emitted, so the SSM pool group got no min_slots floor and the ratio-based grain split rounded it to 31 slots, below the 34 live/dummy slots __init__ requires.
• Fix: Append a constraint of _max_resident_sequences() + reserved-dummy zero-capacity KVCacheDescs, which floors the SSM pool without adding attention pages.
• Automated fix generated by repair-bot

Test plan

• Verify fix on the same GPU type as the original failure
• Check for regressions in related tests

Links

• Bug: https://nvbugs/6525898

Dev Engineer Review

• Consolidates required SSM slot sizing through _num_required_state_slots().
• Adds zero-capacity KVCacheDesc constraints for required live and dummy slots.
• Prevents the V2 Mamba SSM pool from being under-allocated when avg_seq_len is unset.
• Does not increase attention page allocation.
• Removes one valid waiver entry without unrelated configuration changes.

QA Engineer Review

• Modified test_v2_hybrid_typical_batch_splits_capacity_across_ssm_states_and_dummies.
• Added test_v2_hybrid_constrains_ssm_pool_to_live_slot_floor.
• Neither test is listed in tests/integration/test_lists/ for CI (test-db/) or manual QA (qa/) coverage.
• Verdict: needs follow-up.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Enterprise

Run ID: 004948f6-df68-421b-b5f5-111fbc7ba163

📥 Commits

Reviewing files that changed from the base of the PR and between 8bc2e14 and e68d27d.

📒 Files selected for processing (3)

• tensorrt_llm/_torch/pyexecutor/mamba_cache_manager.py
• tests/integration/test_lists/waives.txt
• tests/unittest/_torch/executor/test_mamba_cache_manager.py

🚧 Files skipped from review as they are similar to previous changes (2)

• tests/integration/test_lists/waives.txt
• tensorrt_llm/_torch/pyexecutor/mamba_cache_manager.py

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Walkthrough

MambaHybridCacheManagerV2 now centralizes required live state-slot calculation and applies the full live and reserved-dummy slot floor to SSM cache constraints. Regression coverage was added, and one integration waiver was removed.

Changes

Mamba SSM cache floor

Layer / File(s)	Summary
Centralize required state slots tensorrt_llm/_torch/pyexecutor/mamba_cache_manager.py	Adds _num_required_state_slots() and uses it for initialization and minimum live GPU quota calculation.
Enforce and validate the SSM floor tensorrt_llm/_torch/pyexecutor/mamba_cache_manager.py, tests/unittest/_torch/executor/test_mamba_cache_manager.py, tests/integration/test_lists/waives.txt	Adds an SSM constraint for all required live and reserved-dummy slots, reuses a shared zero-capacity descriptor, adds regression coverage, and removes the related integration waiver.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• NVIDIA/TensorRT-LLM#17107: Both changes modify MambaHybridCacheManagerV2 and its tests, but address different cache-slot behaviors.
• NVIDIA/TensorRT-LLM#17131: Both changes preserve required SSM state-slot capacity when avg_seq_len is unset.

Suggested reviewers: simengliu-nv, schetlur-nv

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the bug fix and describes the added constraint for required Mamba cache slots.
Description check	✅ Passed	The description explains the root cause and fix, links the bug, and includes a test plan; the omitted checklist does not prevent review.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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