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[KVEvent] User request.block_hash for parent block_hash#30544

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vllm-bot merged 3 commits into
vllm-project:mainfrom
heheda12345:fix_kv_event
Dec 24, 2025
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[KVEvent] User request.block_hash for parent block_hash#30544
vllm-bot merged 3 commits into
vllm-project:mainfrom
heheda12345:fix_kv_event

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@heheda12345

@heheda12345 heheda12345 commented Dec 12, 2025 •
edited by github-actions Bot
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Purpose

Parent block can be a null block:

  • mamba: the block_table will be like [null_block, null_block, ..., null_block, normal_block] as we only need one block per decode step.
  • sliding window + kv cache connector, assume block_size 1, window size 2, hit 3 local tokens + 3 external tokens, the block table will be [NULL, NULL, NULL, NULL, 4, 5]
    we will do:
# first allocation
allocate_slots(delay_cache_blocks=True):
    save_new_computed_blocks() caches the first 3 blocks
# after kv cache transfer
allocate_slots(delay_cache_blocks=False):
    cache_blocks() caches the first 6 blocks, parent block is block 2 (null_block)

So we extract parent block hash from request.block_hashes instead of null_block

Test Plan

Test Result

Essential Elements of an Effective PR Description Checklist
  • The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
  • The test plan, such as providing test command.
  • The test results, such as pasting the results comparison before and after, or e2e results
  • (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.
  • (Optional) Release notes update. If your change is user facing, please update the release notes draft in the Google Doc.

@heheda12345
init
93935aa 
Signed-off-by: Chen Zhang <zhangch99@outlook.com>
@heheda12345
fix
5073e6d 
Signed-off-by: Chen Zhang <zhangch99@outlook.com>
@mergify mergify Bot added the v1 label Dec 12, 2025
gemini-code-assist[bot]
gemini-code-assist Bot reviewed Dec 12, 2025
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Code Review

This pull request addresses a potential AssertionError that could occur when determining the parent block hash for KV cache events. The issue arises in scenarios where the parent block is a null_block, which does not have an associated block hash, causing the assertion to fail. The proposed change correctly resolves this by retrieving the parent block hash directly from request.block_hashes. This is the correct approach as request.block_hashes represents the logical sequence of hashes and is the reliable source of truth, independent of the physical block implementation. The fix is clean, direct, and I find no issues with the implementation.

@heheda12345 heheda12345 mentioned this pull request Dec 12, 2025
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mgoin
mgoin approved these changes Dec 14, 2025
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Seems reasonable to me. Should we add a unit test if this failed in some case?

@heheda12345 heheda12345 mentioned this pull request Dec 18, 2025
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5 tasks
@ivanium
test: add unit test case for null parent block hash
77f6531 
Signed-off-by: Yifan Qiao <yifanqiao@berkeley.edu>
@ivanium

ivanium commented Dec 18, 2025 •
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Seems reasonable to me. Should we add a unit test if this failed in some case?

Good idea. I added a test case for null parent block hash. PTAL

@heheda12345 heheda12345 enabled auto-merge (squash) December 21, 2025 23:30
@github-actions github-actions Bot added the ready ONLY add when PR is ready to merge/full CI is needed label Dec 21, 2025
@vllm-bot vllm-bot merged commit 538e830 into vllm-project:main Dec 24, 2025
46 of 47 checks passed
yiliu30 pushed a commit to yiliu30/vllm-fork that referenced this pull request Dec 30, 2025
@heheda12345 @ivanium @yiliu30
[KVEvent] User request.block_hash for parent block_hash (vllm-project…
f225056 
…#30544)

Signed-off-by: Chen Zhang <zhangch99@outlook.com>
Signed-off-by: Yifan Qiao <yifanqiao@berkeley.edu>
Co-authored-by: Yifan Qiao <yifanqiao@berkeley.edu>
mystous pushed a commit to mystous/vllm_hybrid that referenced this pull request May 10, 2026
@heheda12345 @ivanium
[KVEvent] User request.block_hash for parent block_hash (vllm-project…
64130aa 
…#30544)

Signed-off-by: Chen Zhang <zhangch99@outlook.com>
Signed-off-by: Yifan Qiao <yifanqiao@berkeley.edu>
Co-authored-by: Yifan Qiao <yifanqiao@berkeley.edu>
my-other-github-account pushed a commit to my-other-github-account/vllm that referenced this pull request May 15, 2026
@heheda12345 @ivanium
[KVEvent] User request.block_hash for parent block_hash (vllm-project…
08aa87b 
…#30544)

Signed-off-by: Chen Zhang <zhangch99@outlook.com>
Signed-off-by: Yifan Qiao <yifanqiao@berkeley.edu>
Co-authored-by: Yifan Qiao <yifanqiao@berkeley.edu>
my-other-github-account pushed a commit to my-other-github-account/vllm that referenced this pull request May 15, 2026
@heheda12345 @ivanium
[KVEvent] User request.block_hash for parent block_hash (vllm-project…
f074dfd 
…#30544)

Signed-off-by: Chen Zhang <zhangch99@outlook.com>
Signed-off-by: Yifan Qiao <yifanqiao@berkeley.edu>
Co-authored-by: Yifan Qiao <yifanqiao@berkeley.edu>
0826joyce pushed a commit to 0826joyce/vllm-serving-optimization that referenced this pull request May 19, 2026
@heheda12345 @ivanium
[KVEvent] User request.block_hash for parent block_hash (vllm-project…
2c590e5 
…#30544)

Signed-off-by: Chen Zhang <zhangch99@outlook.com>
Signed-off-by: Yifan Qiao <yifanqiao@berkeley.edu>
Co-authored-by: Yifan Qiao <yifanqiao@berkeley.edu>
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