A single cudaHostRegister over a >~1 TB host buffer fails with
cudaErrorMemoryAllocation on B300 (hard per-call ceiling: 512 GiB OK, 1024 GiB
FAIL), crashing the hicache_size=1600 (~1.5 TB CP shared-L2 slab) prefill at
startup. The registration cannot simply be chunked: a memcpy (cudaMemcpyBatchAsync,
the CP-L2 H2D/D2H transfer) fails with cudaErrorInvalidValue when its host range
straddles a registration boundary (verified empirically on b300-049).
Fix: physically split the host cache into multiple page-aligned slabs, each <= a
safe single-registration size (default 480 GiB, env SGLANG_CP_HICACHE_MAX_SLAB_GB),
reusing the existing SharedHostTensorGroupAllocator + per-slab transfer splitting
(_host_transfer_segments). Each slab is one whole registration and no transfer
crosses a boundary; small configs (hicache_size<=400) stay single-slab unchanged.
- memory_pool_host.py: add cp_hicache_max_single_register_bytes() + the fail-loud
_check_single_cuda_host_register_size guard; revert the (transfer-unsafe)
registration chunking back to one cudaHostRegister per buffer/slab.
- hiradix_cache.py: _cp_shared_l2_slab_pages_by_payload auto-caps each payload's
slab <= the ceiling so large caches auto-split.
- cp_l3_slab_accessor.py: CpSharedL2SlabAccessor is now slab-count-aware
(CpL3SlabSpan + per-slab dispatch via global_base_page; per-slab layer stride);
_cp_l3_slab_spans rewires _maybe_init_cp_l3 off the single-slab assumption. L3
disk slabs / slot pool / LMDB index / GC are content-addressed and unchanged.
Tests: multi-slab accessor incl. a non-circular torch.frombuffer-layout check; a
real allocate_group + _cp_l3_slab_spans roundtrip; slab-cap auto-split; L3 store
cross-slab spill/reload. Reviewed by 3 adversarial agents, no correctness bugs.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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