[KV Offload] Return None from lookup() for in-flight blocks

[ronensc]

Purpose

CPUOffloadingManager.lookup() was returning False for both absent blocks and in-flight blocks (write started but not yet complete).
The base class defines None to mean "retry later" which is the right semantic for in-flight.
This makes the scheduler defer instead of treating an in-flight block as a miss.

Test Plan

pytest -v -s tests/v1/kv_offload/cpu/test_manager.py

Test Result

tests/v1/kv_offload/cpu/test_manager.py::test_already_stored_block_not_evicted_during_prepare_store[lru] PASSED
tests/v1/kv_offload/cpu/test_manager.py::test_already_stored_block_not_evicted_during_prepare_store[arc] PASSED
tests/v1/kv_offload/cpu/test_manager.py::test_cpu_manager PASSED
tests/v1/kv_offload/cpu/test_manager.py::TestARCPolicy::test_basic PASSED
tests/v1/kv_offload/cpu/test_manager.py::TestARCPolicy::test_t1_to_t2_promotion PASSED
tests/v1/kv_offload/cpu/test_manager.py::TestARCPolicy::test_eviction_with_load PASSED
tests/v1/kv_offload/cpu/test_manager.py::TestARCPolicy::test_adaptive_target PASSED
tests/v1/kv_offload/cpu/test_manager.py::TestARCPolicy::test_t1_t2_eviction_policy PASSED
tests/v1/kv_offload/cpu/test_manager.py::TestARCPolicy::test_ghost_list_bounds PASSED
tests/v1/kv_offload/cpu/test_manager.py::TestARCPolicy::test_touch_ordering PASSED
tests/v1/kv_offload/cpu/test_manager.py::TestARCPolicy::test_failed_store PASSED
tests/v1/kv_offload/cpu/test_manager.py::TestARCPolicy::test_full_scenario PASSED
tests/v1/kv_offload/cpu/test_manager.py::test_filter_reused_manager PASSED

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[claude]

Claude Code Review

This pull request is from a fork — automated review is disabled. A repository maintainer can comment @claude review to run a one-time review.

[gemini-code-assist]

Code Review

This pull request updates the lookup method in the CPU manager to distinguish between a missing block and an in-flight write. Previously, the method returned a boolean indicating readiness; it now returns False if the block is not found, None if a write is in-flight, and True if the block is ready. The unit tests have been updated to reflect these new return values. I have no feedback to provide as there were no review comments to evaluate.

[orozery]

Now we don't test the False flow.

Can you add one assert for a lookup returning False?

[ronensc]

A few lines later in the test there are already several assertions covering the False case. Should I add another assertion here as well?

vllm/tests/v1/kv_offload/cpu/test_manager.py

Line 180 in 29609a8

assert cpu_manager.lookup(to_key(3), _EMPTY_REQ_CTX) is False

[orozery]

Missed it, right.