[jordicor]

On a 32 GB Windows 11 laptop with an RTX 4080 Laptop and a Thunderbolt RTX 3090, file-backed expert pages remained in the engine's working set after their GPU copies. With IQ2_XS and the existing layer split, available RAM stayed near 0.5 GiB during the measured workload.

This adds opt-in Windows mapped-page release via STRATA_ARENA_RELEASE=1. Unset or 0 preserves the current behavior.

• Implement FileExpertSource::release() for experts.bin and direct GGUF file views using Windows working-set trimming. Preserve shared boundary pages and never trim private/pinned staging buffers.
• Release pages after prefill's lent expert slots have finished refilling, in both serving and one-shot generation. Existing completed-upload release calls also use the implementation.
• Add focused C++ coverage, document the switch and tradeoff, and include the benchmark scripts and scoped measurements.

Measured result

The same prototype executable was run with explicit release OFF and ON: one warmup and three fresh requests each at 1K, 4K and 16K prompt tokens, 256 output tokens, context 32768, int8 KV, MTP, --mmap-experts --layer-split 12 --trim-stage-weights.

Metric	OFF	ON
Available physical RAM, median	0.512 GiB	12.187 GiB
Available physical RAM, minimum	0.277 GiB	6.110 GiB
Engine working set, median	23.379 GiB	11.946 GiB
System commit, median	51.880 GiB	51.973 GiB
Physical SSD reads, total	16.750 GiB	16.809 GiB

Prefill throughput was 3.7-4.4% lower. This improves physical-memory availability on this machine; it does not reduce commit, demonstrate fewer SSD reads, or establish a general speed improvement. Runs were sequential, the OS file cache was retained, and generated code-explanation responses differed. The submitted patch defaults to OFF; the measured prototype defaulted to ON, but both benchmark arms set the switch explicitly.

Full configuration, individual timings, hashes, reproduction commands and limitations: measurement report.

Validation

• Fresh Windows Release build with MSVC 2019 and CUDA 13.1, SM 86/89, native experts enabled.
• file_expert_source_test and expert_layout_test pass in separate processes with the switch unset, 0, and 1: page alignment and working-set behavior, unchanged bytes after repeated reads, invalid indices, closed sources, and three GGUF roles across two shards.
• Eight benchmark-harness tests pass.
• Final rebuilt engine completes fresh 1K/4K inference requests on both GPUs with release enabled.

The prototype also completed 30 functional requests without runtime errors. All 24 objective responses/statuses matched the official engine at the same placement: 21 passes and three unchanged Markdown-fenced-JSON failures; six prose responses were unscored. These limited checks do not prove general output parity.

Related prior work: #467 and #640. The existing multi-GPU implementation is reused; this PR contributes Windows mapped-page release.

[Niko1221]

Merged in 0.1.40 with one change: the switch is STRATA_FILE_RELEASE=1, because STRATA_ARENA_RELEASE already exists and means the opposite (=0 keeps the experts a GPU holds). Default off. The bench folder keeps the README and the two scripts.