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fix(server): agents yield CPU, tasks, and reclaim to the server under pressure#27176

merged2
main
agent-slice-weights
opened1d agobyJJulius Marminge
4 files changed
View on GitHubTwo-way sync enabledPR last imported 1d ago

On 2026-10-29, agents filled T3's agents slice. The kernel's reclaim and IO storm that followed (1.3 GB/s page-ins, load 94 on 16 cores) slowed the server too: one SessionStore.verify SQLite read took 5.9 s. The agents slice only had MemoryHigh/MemoryMax. That left three gaps:

  • Outside the boot service (desktop app, npx t3), agents and the server got equal CPU weight.
  • Agents could use the user's whole task budget.
  • Global reclaim treated the server's pages like any agent's.

Changes

  • app-t3code.slice gets CPUWeight=10 IOWeight=10 TasksMax=25% at runtime, through the same probe → set-property --runtime → log-on-failure path the memory limits already use. The properties go on the parent, not on app-t3code-agents.slice. Weights only compete among siblings, and app-t3code-agents.slice has none: the owned per-state-dir slices are its children. Its parent is what competes with t3code.service, or with the desktop/terminal scope that hosts the server, under app.slice.
    • CPU: the boot unit already wins 1000:100. This makes it 1000:10, and 100:10 for a desktop or terminal server, which was 1:1 before.
    • TasksMax=25% (of the kernel task max) keeps agents below logind's default 33% per-user limit. A fork storm then can't stop the server from spawning git or providers.
  • The boot unit gets MemoryLow=1536M. That covers the live server's working set (about 0.9 GB anon plus mapped binaries and hot SQLite pages) with headroom. It matches what the fleet resource guard has run in production. The unit text changes, so status.current turns false and the next t3 update / t3 service install rewrites it. That rewrite replaces the whole file, so running it again is a no-op.

What these do not do on a stock host (stated plainly)

  • CPUWeight only works where the cpu controller is delegated to the user manager. Current systemd delegates cpu memory pids by default; older managers accept the property and ignore it.
  • IOWeight (on the agents and on the server) only works when the io controller is delegated to the user manager. By default systemd delegates cpu memory pids, so it is accepted and ignored there. It costs nothing, and it takes effect where an admin delegates io (with a weight-aware scheduler).
  • MemoryLow is capped by the protection set on its ancestors (user.slice, user-$UID.slice, user@$UID.service), even with memory_recursiveprot. Only root can set that. On a stock host it is inert. Where the admin grants it (as on nucbox-1), reclaim takes the agents' unprotected pages first.
  • No MemoryMin. It is a hard guarantee. On small VPS hosts it can force OOM kills elsewhere, and MemoryLow already orders reclaim.

agentSliceMemoryLimits: left unchanged

The hours-long freeze happens in the MemoryHigh→MemoryMax band. The kernel throttles allocations and reclaims the agents' own pages, but never kills. The only way to shrink that band is to drop MemoryHigh or move it up to MemoryMax. Either way agents reach MemoryMax sooner, and that means OOM kills. That is the automatic killing we decided against; the Force-stop and memory-pressure-indicator PR covers it. Lowering both limits would also kill sooner. Raising them would leave the server less than 6 GB of headroom, and on stock hosts that headroom is its only memory protection. So the current numbers stay.

Tests

  • agentScope.test.ts: the exact set-property arguments for both slices.
  • bootService.test.ts: the [Service] section carries the weights, MemoryLow, and OOMPolicy=continue.
  • vp run check:changed passes. No runtime experiments were run on the live host.

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b4f0aec
MmacroscopeappBot1d ago
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Approvability

Verdict: Needs Human Approval

Macroscope's review found this PR requires human approval — This changes Linux resource-allocation defaults to favor the server over agents, including a shared task ceiling and server memory protection. Human review must confirm the intended tradeoff between server responsiveness and agent concurrency across supported hosts.

No code changes detected at b4f0aec. Prior analysis still applies.

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Ggithub-actionsBot1d ago
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Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

ProviderMetricMain baselineThis PRImpactPR ceiling
CodexTotal thread wire5.0 KiB5.0 KiB−6 B (−0.1%)6.8 KiB✅
CodexThread snapshot wire3.8 KiB3.8 KiB0 B (0.0%)4.9 KiB✅
CodexLive turn WebSocket wire1.3 KiB1.2 KiB−6 B (−0.5%)2.0 KiB✅
CodexLive turn WebSocket decoded21.6 KiB21.6 KiB0 B (0.0%)24.4 KiB✅
CodexLive turn messages220 (0.0%)8✅
ClaudeTotal thread wire5.1 KiB5.1 KiB0 B (0.0%)6.8 KiB✅
ClaudeThread snapshot wire3.8 KiB3.8 KiB0 B (0.0%)4.9 KiB✅
ClaudeLive turn WebSocket wire1.3 KiB1.3 KiB0 B (0.0%)2.0 KiB✅
ClaudeLive turn WebSocket decoded21.9 KiB21.9 KiB0 B (0.0%)24.4 KiB✅
ClaudeLive turn messages220 (0.0%)8✅

Baseline: 812c0a7 · PR result: b4f0aec · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

  • Codex decoded thread snapshot: 108.5 KiB
  • Claude decoded thread snapshot: 108.8 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.

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Walkthrough

The boot service unit gains MemoryLow=1536M. Agent processes retain their calculated memory limits, while the parent server slice gains CPU, I/O, and task limits.

Changes: Systemd resource controls

Layer / File(s)Summary
Boot service memory protection
apps/server/src/cloud/bootService.ts, apps/server/src/cloud/bootService.test.ts		The rendered unit adds MemoryLow=1536M. A test checks the CPU and I/O weights, memory reservation, and OOM policy in the [Service] section.
Agent slice resource limits
apps/server/src/process/agentScope.ts, apps/server/src/process/agentScope.test.ts		The agent slice retains its calculated memory limits. The parent server slice receives CPU, I/O, and task limits. A shared helper applies properties and logs command failures; a test checks both slice updates.

Priority: External image Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Medium

Possibly related issues

  • pingdotgg/t3code issue 26004: The boot unit gains MemoryLow, addressing the missing server memory protection described in the issue.
  • pingdotgg/t3code issue 26171: The boot unit adds a memory reservation and documents ancestor protection limits. The issue’s placement and OOM-score concerns are not changed.

Suggested reviewers: t3dotgg, macroscopeapp

Merge Risk: External image Moderate · previous review eb328

On hosts without administrator-configured ancestor protection, the new memory reservation may not protect the server during agent memory pressure. Resolve or explicitly accept that deployment requirement before merging.

Pre-merge checks: Passed 3 · Failed 1

Failed Failed checks: 1 warning

Check nameStatusExplanationResolution
Description checkWarningThe description follows the template's sections. It gives a problem (the 2026-10-29 incident and three gaps), a change section that explains the slice properties and the boot unit's MemoryLow, and a s…Scope and approval section has no link. The template asks for a triaged bug issue or a discussion with maintainer approval, or an explanation for a small, focused fix that does not need a prior issue. The description does not link an issue …
Passed Passed checks: 3 passed
Check nameStatusExplanation
Title checkPassedThe title names the main change: agents are limited so they yield CPU, tasks, and memory reclaim to the server under pressure. The changeset adds CPUWeight=10, IOWeight=10, and TasksMax=25% to app-t3c…
Linked Issues checkPassedCheck skipped because no linked issues were found for this pull request.
Out of Scope Changes checkPassedCheck skipped because no linked issues were found for this pull request.
Full details: Title check

Explanation

The title names the main change: agents are limited so they yield CPU, tasks, and memory reclaim to the server under pressure. The changeset adds CPUWeight=10, IOWeight=10, and TasksMax=25% to app-t3code.slice, and MemoryLow=1536M to the boot unit. The title matches the stated objective, and the conventional commit format fits the repository template example.

Full details: Description check

Explanation

The description follows the template's sections. It gives a problem (the 2026-10-29 incident and three gaps), a change section that explains the slice properties and the boot unit's MemoryLow, and a scope section that explains why agentSliceMemoryLimits is unchanged. It also includes tests and notes what was not checked on a live host.

Resolution

Scope and approval section has no link. The template asks for a triaged bug issue or a discussion with maintainer approval, or an explanation for a small, focused fix that does not need a prior issue. The description does not link an issue or discussion, and it does not explain why the change qualifies without one. Add the link or the explanation.

Verification section needs more detail. The description says vp run check:changed passes and lists the test assertions. It does not show observed results of those tests. It also says no runtime experiments were run on the live host. The template asks for the focused checks and the observed results for the changed behavior, and it asks the author to state anything not checked. Add the observed test output or results for the changed behavior.

The Problem section mentions a reproduction environment, but it does not give reproduction steps. Add a short reproduction, or state why one is not available.

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CcoderabbitaiBotreviewed · 2 inline threads1d ago
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Actionable comments posted: 2

  • 🪄 Fix comments: Fix CodeRabbit comments on this PR
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6Inline comments:
7Review comments at @apps/server/src/cloud/bootService.ts:
8- Line 118: Update the cgroup configuration associated with the MemoryLow=1536M
9entry so intermediate ancestors such as app.slice also provide protection when
10memory_recursiveprot is unavailable; verify the full ancestor chain preserves
11the intended effective MemoryLow.
12
13Review comments at @apps/server/src/process/agentScope.ts:
14- Line 26: Add a note next to AGENTS_PARENT_PROPERTIES stating that CPUWeight
15requires the cpu controller to be delegated to the user manager, and document
16the same requirement in the PR description or operator docs.
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External image Files selected for processing: 4
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apps/server/src/cloud/bootService.tsline 118Outdated · 829620cResolved by Julius Marminge
apps/server/src/process/agentScope.tsline 26Outdated · 829620cResolved by Julius Marminge

Added 2 commits

  • fix(server): agents yield CPU, tasks, and reclaim to the server under pressure221693e
  • docs(server): agent slice weights need delegated cgroup controllersb4f0aec