fix: allow HMA with KV events when explicitly enabled#39269
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This pull request modifies the configuration logic in vllm/config/vllm.py to allow the hybrid KV cache manager to be used with KV events if explicitly enabled via the scheduler configuration. Previously, the hybrid KV cache manager was automatically disabled whenever KV events were configured. I have no feedback to provide.
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The Hybrid Memory Allocator (HMA) is unconditionally disabled when kv_events_config is set, even when the user explicitly passes --no-disable-hybrid-kv-cache-manager. This blocks disaggregated serving for hybrid models (Mamba+attention) like Nemotron-H, despite NixlConnector already implementing SupportsHMA with full Mamba support (_has_mamba detection, MAMBA2_ATTN backend handling). Fix: Only auto-disable HMA for KV events when the user has not explicitly opted in. When --no-disable-hybrid-kv-cache-manager is passed (disable_hybrid_kv_cache_manager=False), respect it. Tested with: - NVIDIA Nemotron-3-Super-120B-A12B-NVFP4 (hybrid Mamba+attention) - Disaggregated prefill/decode via NixlConnector with CUDA-aware UCX - 200/200 requests successful in production benchmark Signed-off-by: sara4dev <saravanakumar.periyasamy@gmail.com>
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This pull request has merge conflicts that must be resolved before it can be |
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Summary
Allow the Hybrid Memory Allocator (HMA) to work alongside KV events when explicitly enabled via
--no-disable-hybrid-kv-cache-manager. This unblocks disaggregated serving for hybrid models (Mamba + attention) like NVIDIA Nemotron-H.The problem: HMA is unconditionally disabled when
kv_events_configis set (line 1226-1228 ofvllm/config/vllm.py), even when the user explicitly passes--no-disable-hybrid-kv-cache-manager. This blocks disaggregated serving for hybrid models despiteNixlConnectoralready implementingSupportsHMAwith full Mamba support (_has_mambadetection,MAMBA2_ATTNbackend handling).The fix: Only auto-disable HMA for KV events when the user hasn't explicitly opted in. When
--no-disable-hybrid-kv-cache-manageris passed (disable_hybrid_kv_cache_manager=False), respect it.Changes
vllm/config/vllm.py: Add check for explicit user opt-in before disabling HMA due to KV events config (+8 lines, -2 lines)Test Plan
Tested with:
Context
NixlConnector already:
SupportsHMA(kv_connector/v1/base.py)_has_mamba(nixl_connector.py:576)MAMBA2_ATTNattention backend (nixl_connector.py:1216)The config guard at line 1226 was added conservatively but creates a conflict: disaggregated mode auto-enables KV events, which then blocks HMA, making hybrid disagg impossible even though the connector supports it.
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