The Integration That Made Memory Awareness Real: Wiring Memcheck into the Entrypoint

"Now update the registration section to POST memcheck results, and fix the benchmark invocation to pass the budget."

This single sentence, followed by a file edit confirmation, is the pivotal moment where a months-long effort to prevent out-of-memory (OOM) kills on GPU proving workers finally became operational. The message, sent by an AI assistant during an opencode coding session, represents the integration step that connected a newly built memory detection system (memcheck) to the actual runtime configuration of every production instance. Without this edit, the memcheck script would have been a standalone diagnostic tool—informative but inert. With it, the system became self-regulating.

The Problem: OOM Kills on 256GB Machines

To understand why this message matters, one must understand the crisis it addressed. The CuZK proving engine, used for Filecoin proof generation on vast.ai GPU instances, was suffering from frequent OOM kills. The root cause was subtle: CuZK's detect_system_memory() function read total RAM from /proc/meminfo, which reports the host machine's physical memory. But Docker containers have their own cgroup memory limits, often much lower than the host's total. A 256GB host might allocate only 64GB to a container. CuZK would see 256GB, assume it could use most of it, and then get killed by the kernel when it exceeded the container's actual limit.

The fix required a multi-layered solution: a shell script (memcheck.sh) that detects cgroup v1/v2 memory limits, checks RLIMIT_MEMLOCK for GPU pinning capability, gathers GPU info via nvidia-smi, and calculates safe concurrency levels; a vast-manager API endpoint to receive and store these reports; a dashboard UI to display them; and finally—the subject of this article—integration into the instance lifecycle script (entrypoint.sh) so the detected values actually influence runtime behavior.

The Message in Context

The subject message ([msg 3857]) is the second of four consecutive edits to entrypoint.sh that together wire memcheck into the production pipeline. It follows [msg 3856], where the assistant outlined the plan:

"Now integrate memcheck into entrypoint.sh. Key changes: 1. Run memcheck.sh after registration, POST to manager 2. Use memcheck results to set correct BUDGET and BENCH_CONCURRENCY 3. Add CURIO_NODE_NAME 4. The supervisor loop already handles auto-restart (it's already there at line 278)"

Message 3857 narrows the focus to two specific sub-tasks: updating the registration section to POST memcheck results, and fixing the benchmark invocation to pass the budget. The subsequent messages ([msg 3858] and [msg 3859]) continue refining—updating the benchmark invocation again and then the production run.sh call.

This iterative, surgical approach reveals the assistant's working style: rather than making one massive edit that touches everything at once, it breaks the integration into small, verifiable steps. Each edit is a focused change with a clear purpose, making it easier to reason about correctness and to recover if something goes wrong.

Why POST Memcheck Results?

The decision to POST memcheck results to the vast-manager API during the registration phase reflects a deliberate architectural choice. The memcheck data serves two distinct purposes:

1. Operational visibility: The vast-manager dashboard displays memcheck results alongside each instance, allowing operators to see memory pressure, pinning capability, and recommended concurrency levels at a glance. This is essential for debugging OOM issues and for capacity planning.
2. Dynamic configuration: The same data is used immediately to set BUDGET and BENCH_CONCURRENCY environment variables before the benchmark phase begins. This prevents the benchmark itself from triggering an OOM kill—a failure mode that had been observed in production. By POSTing during registration (the earliest phase of the instance lifecycle), the data is available for both purposes before any proving work begins. The assistant's choice to do this in the registration section, rather than later in the lifecycle, shows an understanding that memory configuration must be established before the memory-intensive benchmark phase, not after.

Why Pass the Budget to the Benchmark

The "fix the benchmark invocation to pass the budget" part of the message addresses a specific failure mode. Previously, the benchmark script (benchmark.sh) would start a cuzk daemon with default memory settings—settings that, as established above, could be dangerously wrong. If the daemon consumed more memory than the container's cgroup limit allowed, the kernel would kill it, the benchmark would fail, and the entire instance would be torn down by vast-manager's failure handling.

Passing the budget explicitly means the benchmark daemon starts with a memory limit that respects the container's actual constraints. This is a textbook example of "fail fast" being replaced by "configure correctly"—instead of letting the process crash and then handling the failure, the system prevents the crash by setting appropriate limits upfront.

Assumptions Embedded in This Edit

The assistant makes several assumptions in this message, most of them reasonable but worth examining:

The memcheck.sh script exists and is correct. The assistant wrote memcheck.sh in [msg 3820], but at this point it has not been tested on a real vast.ai instance. The assumption is that its cgroup detection logic works correctly across the diverse range of Docker configurations found on vast.ai hosts.

The vast-manager API is already deployed. The API endpoint (POST /memcheck) was added in [msg 3833], but the Go binary needs to be rebuilt and deployed. The assistant is editing the entrypoint script in the Docker image layer, assuming the API will be available when instances run.

The supervisor loop handles auto-restart. Point 4 in the plan from [msg 3856] explicitly notes this assumption. The assistant verified by reading the entrypoint code that the supervisor loop at line 278 already restarts cuzk and curio on crash. This is correct—the supervisor was implemented earlier in the session—but it's worth noting that the assistant initially misunderstood the restart behavior (see the reasoning in [msg 3819]) and had to correct itself.

The BUDGET and BENCH_CONCURRENCY variables are consumed correctly downstream. The assistant assumes that run.sh and benchmark.sh already accept these variables or can be easily modified to do so. Messages [msg 3858] and [msg 3859] show this assumption being validated through additional edits.

Potential Mistakes and Incorrect Assumptions

While the message itself is straightforward, the broader context reveals a few risks:

The edit is not shown. The message confirms "Edit applied successfully" but does not display the diff. This is a limitation of the tool interface, not a mistake per se, but it means the reader cannot verify what exactly changed. The correctness of the edit depends entirely on the assistant's internal model of the file state.

Sequential edits to the same file risk conflicts. Messages 3856, 3857, 3858, and 3859 all edit entrypoint.sh. If any edit introduces a subtle formatting issue or duplicates a line, it could break the script. The assistant's approach of making small, focused edits mitigates this risk, but it does not eliminate it.

No validation step between edits. The assistant does not run a syntax check or a dry run after each edit. The set -euo pipefail in entrypoint.sh means that certain errors would be caught at runtime, but structural issues (like a missing fi or an unterminated heredoc) would only be discovered when the script actually runs on an instance.

Input Knowledge Required

To understand this message fully, one needs:

• Knowledge of the entrypoint.sh lifecycle: The script runs in phases—port availability check, tunnel setup, registration with vast-manager, parameter fetching, benchmark, and finally the production supervisor loop. The "registration section" referenced in the message is the phase where the instance announces itself to the manager.
• Understanding of cgroup memory limits: The core problem is that Docker containers have memory limits invisible to naive system queries. Memcheck exists specifically to detect these limits.
• Familiarity with the CuZK proving engine's budget system: The BUDGET variable controls how much memory the proving engine can allocate. Setting it correctly is the primary mechanism for preventing OOM kills.
• Knowledge of the vast.ai instance lifecycle: Instances are provisioned, register with a management server, download proving parameters, run a benchmark to establish a rate, and then enter a supervisor loop that handles production proving work. Failure at any phase (except the supervisor loop) typically results in the instance being destroyed and replaced.

Output Knowledge Created

This message creates:

• A self-regulating instance lifecycle: The entrypoint script now automatically detects memory constraints and adjusts its behavior accordingly, without human intervention.
• Persistent memory telemetry: By POSTing memcheck results to the vast-manager API during registration, the system creates a historical record of memory conditions across all instances, viewable in the dashboard.
• A precedent for dynamic configuration: The pattern established here—detect, report, configure—can be extended to other runtime parameters (GPU temperature, network bandwidth, disk I/O) in the future.

The Thinking Process Visible in the Reasoning

While the subject message itself is terse, the preceding message ([msg 3856]) reveals the assistant's reasoning process explicitly. The assistant lists four key changes, prioritizes them, and notes an important discovery: "The supervisor loop already handles auto-restart (it's already there at line 278)." This discovery, made during an earlier code reading ([msg 3819]), shaped the entire integration. Initially, the assistant thought the supervisor loop might need to be built from scratch. Only after reading the actual code did it realize the loop already existed, allowing it to focus on the missing pieces: memcheck integration and budget configuration.

This is a classic pattern in software engineering: reading the existing code before writing new code. The assistant's willingness to correct its own assumptions—"Wait, re-reading the user's request..." in [msg 3819]—is a sign of careful reasoning.

Conclusion

Message 3857 is a small edit with outsized consequences. It transforms memcheck from a diagnostic tool into an active component of the production system. The edit itself is simple—a few lines added to a shell script—but the reasoning behind it encompasses the entire OOM prevention strategy: detect the real memory limit, report it to the management layer, and use it to configure the proving engine before it starts. This is the difference between monitoring a problem and solving it.