[KV Offload] Support partial secondary-tier load results - #50321
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Signed-off-by: Moein Khazraee <moein@nvidia.com>
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Signed-off-by: Moein Khazraee <moein@nvidia.com>
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Let's add some usage clarifications
Co-authored-by: Or Ozeri <or@ozery.com> Signed-off-by: Moein Khazraee <moein@nvidia.com>
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…s a miss A failed secondary-tier load livelocks the requesting request (vllm-project#49176): the async lookup cache records a positive verdict per key and nothing corrects it on load failure, so the scheduler re-issues the same doomed promotion every step until the request is aborted. - On a failed load the owning tier marks the cached lookup verdict as a miss (mark_miss), from get_finished_jobs on the scheduler thread. A cached miss is returned on subsequent lookups without re-probing, so the request recomputes on the GPU and never retries it, which structurally cannot loop. The tier already learns of its own failed loads, so no new SecondaryTierManager API is needed. A key is enqueued for probing exactly once, so drain_results asserts that invariant, keeping a late or duplicate result from resurrecting a corrected verdict. - Loads are batched. The C loader reports how many blocks were read before the first failure, so the tier fills JobResult.successful_keys (vllm-project#50321) and marks only the failed block onward as a miss. The manager keeps the blocks that did load in the primary tier, so they stay a hit; only the failed tail is recomputed, and the miss clears when the request finishes. - load_block removes the block file only on a provable short read, in both the C (_load_block) and Python paths. Stores are atomic, so a too-short existing file is genuine corruption; removing it makes future requests miss instead of repeating the failed load. Open failures and read errors leave the file untouched, and a harmless close after a full read no longer fails the load, so a transient host hiccup is not turned into permanent data loss or a spurious miss. This narrows the delete-on-any-error added in vllm-project#49152. Lookup keeps upstream's access-based existence check. Tests: per-tier livelock regressions, partial-batch keep (loaded blocks stay a hit, only the failed tail misses), delete-on-short-read and transient-leaves-file across the C and Python paths, and mark_miss unit tests including the enqueue-once invariant. 345 tiering tests pass (356 with the fs_io_C extension built). Fixes vllm-project#49176 Signed-off-by: Robbie J <RobbieJ@users.noreply.github.com>
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Purpose
This makes secondary-tier fetches best-effort and less tightly coupled to an earlier availability snapshot: losing a few keys only requires recomputing those KV values, while every requested value available at fetch time can still be reused.
The surrounding design already handles lookup, primary-tier allocation, and completion per key. Keys are combined into asynchronous jobs only for transfer efficiency, but JobResult currently reduces the outcome back to one batch-level success value. If any fetch fails, the manager therefore discards the entire batch, including KV blocks fetched successfully.
This PR adds successful_keys to JobResult. For a failed promotion, the manager completes the reported keys successfully and fails only the remainder. An empty collection preserves the existing full-failure behavior, while success=True continues to complete every key. Reported successful keys must belong to the original job.
This also supports more opportunistic secondary tiers: a tier can submit candidate keys based on an earlier query and report the subset that is actually available when the fetch completes, without requiring the query result to remain perfectly accurate throughout the transfer.
This is complementary to #49328, which prevents failed-load livelock by correcting stale lookup verdicts; it does not preserve partially successful load results. No open PR was found implementing this partial-completion contract.
Test Plan
Extend the existing promotion test with two parametrized failure cases:
These functional tests pass and the the existing promotion test covers full success.