Chunk 17.1

In this chunk, the assistant immediately addressed the user's pointed question about the 375 GB peak memory usage by tracing its exact origin in the benchmark code. By reading the pipeline and benchmark source files, the assistant confirmed that the PCE itself is stored in a single static `OnceLock` and is never duplicated across circuits. The 375 GB peak was identified as a benchmark artifact caused by holding the results of both the old-path baseline (~163 GiB) and the PCE path (~125 GiB) simultaneously for validation comparison. The assistant calculated the real production overhead: just 25.7 GiB of static CSR matrix data shared across all pipelines, with the per-pipeline working set remaining at ~21 GiB (unchanged from the old path). The temporary 4.2 GiB witness copy during MatVec is freed before the GPU phase begins. To empirically validate this memory model and demonstrate pipelining behavior, the assistant designed and implemented a new `pce-pipeline` subcommand for `cuzk-bench`. This benchmark features inline RSS tracking via `/proc/self/status`, `malloc_trim` calls to aggressively release memory between phases, a `--compare-old` flag for optional baseline comparison, and a `--parallel` (`-j`) flag to simulate concurrent pipeline execution. Running the sequential benchmark showed RSS dropping cleanly from 155.7 GiB (old path) to 25.8 GiB (PCE static), rising to 181.6 GiB during PCE synthesis, and dropping back to 25.9 GiB after results were dropped—confirming no memory leak. The parallel benchmark with 2 concurrent pipelines peaked at 310.9 GiB (2 × ~156 GiB working set + 25.7 GiB static) and dropped cleanly back to the PCE baseline, validating the memory model for multi-GPU deployments. Throughout this chunk, the assistant maintained rigorous documentation by updating the `cuzk-project.md` file with the Phase 5 memory analysis, the sequential and parallel benchmark results, and the updated roadmap. The work conclusively demonstrated that the PCE's memory overhead is a one-time static cost that scales gracefully with the number of concurrent pipelines, directly addressing the user's core concern about multi-GPU scaling. The findings were staged for commit, solidifying the Phase 5 memory characterization and providing a robust benchmarking tool for future optimization work.

From Phantom to Proof: How a 375 GB Benchmark Artifact Led to a Validated Memory Model for Multi-GPU Proving 2524 words

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