feat(kv-cache): support mixed MLA groups and native offload - #159
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📝 WalkthroughWalkthroughThis change adds configurable DCP replication for DeepSeek sparse-indexer caches, updates indexer metadata handling for global replicated state, and introduces lockstep MLA KV-cache allocation with synchronized block IDs, tensor pools, prefix caching, and expanded validation. ChangesDCP indexer replication
Estimated code review effort: 5 (Critical) | ~120 minutes Sequence Diagram(s)sequenceDiagram
participant Environment
participant DeepseekV32IndexerCache
participant DeepseekV32IndexerMetadataBuilder
participant SparseAttnIndexer
Environment->>DeepseekV32IndexerCache: Configure replicated indexer cache
DeepseekV32IndexerCache->>DeepseekV32IndexerMetadataBuilder: Provide replicated KV-cache spec
DeepseekV32IndexerMetadataBuilder->>SparseAttnIndexer: Build global metadata without DCP localization
SparseAttnIndexer-->>DeepseekV32IndexerMetadataBuilder: Produce global top-k decode metadata
Possibly related PRs
Suggested reviewers: 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
✨ Finishing Touches🧪 Generate unit tests (beta)
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Verify each finding against current code. Fix only still-valid issues, skip the
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Inline comments:
In `@tests/v1/core/test_prefix_caching.py`:
- Line 242: Update the zip call in the block-hash/block-ID pairing loop to pass
strict=True explicitly, preserving the existing iteration while making
mismatched input lengths raise an error.
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📒 Files selected for processing (14)
tests/model_executor/layers/test_sparse_attn_indexer_b12x.pytests/models/test_dcp_shard_draft_defaults.pytests/v1/attention/test_indexer_dcp_localize.pytests/v1/core/test_kv_cache_utils.pytests/v1/core/test_prefix_caching.pytests/v1/worker/test_attn_utils.pytests/v1/worker/test_gpu_block_table.pyvllm/envs.pyvllm/model_executor/layers/sparse_attn_indexer.pyvllm/model_executor/models/deepseek_v2.pyvllm/v1/attention/backends/mla/indexer.pyvllm/v1/core/block_pool.pyvllm/v1/core/kv_cache_coordinator.pyvllm/v1/core/kv_cache_utils.py
| manager.block_pool.blocks[block_id].ref_cnt == 2 for block_id in target_ids | ||
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| for block_hash, block_id in zip(request.block_hashes, target_ids): |
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📐 Maintainability & Code Quality | 🟡 Minor | ⚡ Quick win
Add explicit strict= to zip().
Flagged by Ruff (B905). Lengths match today, but strict=True makes the block-hash/block-id pairing fail loudly if they ever diverge.
Proposed fix
- for block_hash, block_id in zip(request.block_hashes, target_ids):
+ for block_hash, block_id in zip(request.block_hashes, target_ids, strict=True):📝 Committable suggestion
‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.
| for block_hash, block_id in zip(request.block_hashes, target_ids): | |
| for block_hash, block_id in zip(request.block_hashes, target_ids, strict=True): |
🧰 Tools
🪛 Ruff (0.15.21)
[warning] 242-242: zip() without an explicit strict= parameter
Add explicit value for parameter strict=
(B905)
🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.
In `@tests/v1/core/test_prefix_caching.py` at line 242, Update the zip call in the
block-hash/block-ID pairing loop to pass strict=True explicitly, preserving the
existing iteration while making mismatched input lengths raise an error.
Source: Linters/SAST tools
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Independent GG validation on 8x RTX PRO 6000 Blackwell, GLM-5.2 NVFP4, TP8/DCP8/MTP0/A16:
Replication improved DCP8 by 73.3% at 64k and 31.6% at 400k by removing the eight-rank indexer candidate merge. The 64k result is within 1.5% of our TP8/DCP4 result, but replication costs 26.6% of DCP8 KV capacity and remains 22.5% behind DCP4 at 400k. The exact installed overlay passed |
Signed-off-by: Procr <193802945+procr1337@users.noreply.github.com>
build_offloading_config() multiplied every group's block size by the context-parallel factor unconditionally. That was correct when all KV cache groups were CP-sharded, but dcp_replicated groups keep the full cache on every rank, so one of their blocks covers exactly block_size global tokens -- which is why SingleTypeKVCacheManager.__init__ excludes them from the same scaling. The connector therefore saw G * cp where the manager uses G. Since num_gpu_blocks, tokens_per_chunk and hashes_per_chunk all derive from tokens_per_block, the affected group's block and chunk counts came out a factor of cp too small and its offload keys landed on the wrong token boundaries, silently corrupting that group's KV on a load hit. Mirror the manager's rule so both agree on the effective block size. Affects any cp > 1 run combining the offloading connector with a replicated group: DFlash draft groups, the DeepSeek V3.2 sparse indexer, and the DeepSeek V4 compressor. Signed-off-by: Procr <193802945+procr1337@users.noreply.github.com>
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What
Support MLA models that combine a replicated sparse-indexer KV cache with a DCP-sharded main CKV cache.
Compatible MLA groups use distinct physical page geometry while sharing one logical block-ID lifecycle. The same layout can use vLLM's native external KV connector through
--kv-offloading-size.Why
Replicated indexer KV and sharded CKV require different physical block counts and cannot be represented as one uniform cache group. They must nevertheless allocate, cache, promote, and free matching logical block IDs together so attention metadata remains aligned.
Native KV offload must follow the same layout:
Applying DCP scaling to replicated groups gives the offload connector different token boundaries from the KV-cache manager.
How
VLLM_DCP_REPLICATE_INDEXER_CACHE.block_size;block_size * context_parallel_size.The replicated-indexer feature remains disabled by default. Native offload uses the existing
--kv-offloading-sizeoption;VLLM_USE_SIMPLE_KV_OFFLOADis not required.Validation
Automated:
GPU:
nvfp4_ds_mla, FP8 RoPEScope
This PR changes KV-cache grouping, metadata, and native offload behavior. It does not add LMCache, NVMe storage, or model-specific transport code.