feat(config): enable PSI for guest memory pressure signals

[AprilNEA]

The ArcBox idle-balloon controller watches in-guest memory pressure via the agent (arcboxlabs/arcbox#390). Today the agent samples MemAvailable and workingset refault rates from /proc; with CONFIG_PSI the kernel exposes /proc/pressure/{memory,cpu,io} and event triggers, letting the agent upgrade to stall-based detection (kernel-driven wakeups instead of 1s sampling) without any RPC contract change.

Enabled on both architectures. PSI accounting overhead is negligible for VM workloads (ChromeOS/Android ship it enabled); no PSI_DEFAULT_DISABLED, so it works without cmdline changes.

Verified absent today: the 0.6.1 boot-asset kernel image contains no psimon/avg10 strings — the agent currently runs its /proc/meminfo + workingset_refault fallback.

[greptile-apps]

Greptile Summary

This PR enables Linux Pressure Stall Information in both ArcBox kernel configs. The main changes are:

• Adds CONFIG_PSI=y to the ARM64 kernel config.
• Adds CONFIG_PSI=y to the x86_64 kernel config.
• Allows the guest agent to use /proc/pressure stall signals for memory pressure detection.

Confidence Score: 5/5

Safe to merge with minimal risk.

The change is limited to enabling a standard kernel config option in both architecture configs. CONFIG_PROC_FS=y is already present, and no conflicting PSI_DEFAULT_DISABLED setting was found in the changed configs.

No files require special attention.

T-Rex Logs

What T-Rex did

• Ran the PSI configuration validation by executing the validation script and reviewing the after-state log.
• Confirmed that arm64 and x86_64 configurations show CONFIG_PSI=y in the log.
• Noted that CONFIG_PSI_DEFAULT_DISABLED is not present in either file.
• Observed environment blockers: docker and aarch64-linux-gnu-gcc are not available, while make and gcc are present, limiting full validation.

_{Ran code and verified through T-Rex}

Important Files Changed

Filename	Overview
configs/arcbox-arm64.config	Adds built-in CONFIG_PSI=y to the ARM64 kernel config so /proc/pressure is exposed for in-guest pressure monitoring; no issues found.
configs/arcbox-x86_64.config	Adds built-in CONFIG_PSI=y to the x86_64 kernel config so /proc/pressure is exposed for in-guest pressure monitoring; no issues found.

Sequence Diagram

%%{init: {'theme': 'neutral'}}%%
sequenceDiagram
participant KernelConfig as ArcBox kernel config
participant Kernel as Built guest kernel
participant Proc as /proc/pressure/*
participant Agent as ArcBox agent

KernelConfig->>Kernel: "CONFIG_PSI=y"
Kernel->>Proc: expose memory/cpu/io PSI files
Agent->>Proc: detect pressure interface
Proc-->>Agent: pressure stall metrics and triggers
Agent->>Agent: use PSI-based balloon pressure watch

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sequenceDiagram
participant KernelConfig as ArcBox kernel config
participant Kernel as Built guest kernel
participant Proc as /proc/pressure/*
participant Agent as ArcBox agent

KernelConfig->>Kernel: "CONFIG_PSI=y"
Kernel->>Proc: expose memory/cpu/io PSI files
Agent->>Proc: detect pressure interface
Proc-->>Agent: pressure stall metrics and triggers
Agent->>Agent: use PSI-based balloon pressure watch

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_{Reviews (1): Last reviewed commit: "feat(config): enable PSI for guest memor..." | Re-trigger Greptile}