Host HiCache reservations were paying token-level free-slot scans when trying to preserve page contiguity. The allocator now keeps a lazy page-extent index so availability checks and contiguous-preferred allocations avoid materializing the full 220GB-equivalent free-slot metadata path.
The companion benchmark models steady-state L2 churn near full occupancy, including burn-in and historical node-size effects, so LPF/RDMA descriptor quality can be separated from ETE noise.
Constraint: CP HiCache host allocations are page-shaped, but existing callers may still read free_slots directly.
Rejected: Sort and scan free_slots on each alloc_contiguous_preferred call | measured ms-level CPU overhead on 220GB-equivalent metadata.
Rejected: Remove free_slots compatibility | storage/tests still rely on the public tensor surface.
Confidence: medium
Scope-risk: moderate
Directive: Do not reintroduce per-allocation full free_slots scans on HostKVCache; preserve page-extent metadata or benchmark before changing allocator shape.
Tested: Local py_compile for memory_pool_host.py, allocator benchmark, and related tests.
Tested: Local test_cp_hicache_allocator_bench.py 10 passed.
Tested: Remote g0034 test_hicache_controller_cp.py 67 passed; test_cp_hicache_allocator_bench.py 10 passed.
Tested: Remote 220GB-equivalent host_churn benchmark: contiguous path reduced from ms-level to ~30-292us p50 depending on fragmentation.
Not-tested: Full CUDA ETE run after allocator change.
Not-tested: Production long-run fragmentation behavior under live traffic.
The CP shared-KV allocator was still doing total-cache-sized CPU work in the scheduler hot path. That cannot be hidden by GPU overlap, so owner-lane allocation now maintains per-owner free/release buckets and consumes request-sized prefixes instead of rebuilding masks over the full free-page tensor on each request.\n\nThe benchmark was extended to isolate L1 stats, selection, and allocation costs, and the CPU layout tests now install a complete sgl_kernel stub before importing SGLang helpers so remote unit collection does not abort in native extension loading.\n\nConstraint: Allocator CPU work blocks scheduler progress and cannot overlap with GPU forward execution.\nConstraint: CPU unit tests must not load native sgl_kernel on remote images where the loader can SIGABRT.\nRejected: Keep contiguous-run search over full free_pages | still scales with cache capacity and measured multi-ms overhead.\nRejected: Treat remote collection abort as an environment-only issue | it prevented allocator regression coverage and was fixable with a test-local stub.\nConfidence: high\nScope-risk: moderate\nDirective: CP owner-lane allocation is bucket-based; do not reintroduce full free_pages scans on the hot path without benchmark evidence.\nTested: Local py_compile for touched files\nTested: Local benchmark unit test, 6 passed\nTested: Remote benchmark unit test, 6 passed\nTested: Remote test_alloc_pages_with_owners.py, 10 passed\nTested: Remote test_cp_shared_kv_layout.py, 27 passed\nTested: Remote production allocator microbench shows select/alloc p50 reduced from ms-scale to sub-ms scale\nNot-tested: Full ETE traffic run after allocator bucket change
CP shared KV now keeps explicit L1 and host free-room targets so pressure is handled by planned eviction instead of repeated capacity-edge retries. The host allocator gains contiguous-preferred page reservation, L1 owner-lane allocation prefers contiguous physical pages, and CP HiCache metadata preserves pending backup safety for page-granular radix updates. Mooncake transfer stats and allocator microbenchmarks are included to make the remaining transfer bottlenecks measurable rather than inferred.
Constraint: CP shared KV uses decode CP size 1 with all prefill CP ranks participating in transfer, so L1/L2 cache residency must remain page-granular and avoid extra collectives.\nConstraint: Production HiCache can be hundreds of GB, so allocator metadata overhead must be visible before enabling aggressive contiguous allocation broadly.\nRejected: Evict only the exact deficit | this keeps the cache at the cliff and causes repeated evict/allocate pressure.\nRejected: Rely on allocator scans alone for contiguity | remote microbenchmarks show fragmented 220GB-equivalent host metadata can make contiguous-preferred scans multi-ms.\nConfidence: medium\nScope-risk: moderate\nDirective: Do not increase L1/L2 free-room defaults or add new CP collectives without ETE evidence and transfer/allocator measurements.\nTested: python -m py_compile on touched runtime/test/benchmark files.\nTested: PYTHONPATH=. python -m pytest -q test/registered/unit/benchmark/test_cp_hicache_allocator_bench.py => 4 passed, 1 warning.\nTested: Remote g0034 log /mnt/beegfs/cjy/log/sglang_cp_hicache_20260601_233723.log shows active prefill process with L1/L2 free-room args, 702 HTTP 200 chat completions, 6272 prefill batches, and no fatal scheduler traceback in latest scan.\nTested: User-reported L1/L2 cache ETE validation passed on remote run.\nNot-tested: Full local pytest suite; local environment is missing several runtime dependencies.\nNot-tested: CUDA allocator microbenchmark during active production prefill process.\nNot-tested: Mooncake straggler fix; stats show transfer tail latency remains a separate bottleneck.
