fix: keep low-memory boards reachable under load - #464
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Three independent failure modes that each end with a dark panel and no automatic recovery. 1. PluginHealthTracker._load_health_state returned the cached value verbatim. If that value is not a dict, every caller raises AttributeError: 'list' object has no attribute 'get' — during DisplayController.__init__, so the process dies before the display loop starts. systemd restarts it, the same bad entry is read back from disk, and it dies again: an unattended restart loop that survives reboots because the cause is persisted. Observed in the field with plugin_health:<id> holding an unrelated plugin's list payload. Now non-dict entries are discarded with a warning and the defaults are rebuilt. 2. ledmatrix.service used Restart=on-failure, so any exit with status 0 left the unit stopped and the panel dark indefinitely — systemd treats it as success and never brings it back. Restart=always. 3. ledmatrix-wifi-monitor.service used StandardOutput=syslog, which systemd has marked obsolete; it warns and rewrites it to journal on every load. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
On a 1GB Pi 3B+ the display process settles around 600MB RSS of 905MB total. When the remaining headroom runs out the failure is not a clean crash: fork() starts returning ENOMEM, so sshd accepts connections and closes them before its banner, timer jobs stop running, and the panel goes dark, while already-resident processes keep serving normally. The board looks healthy from outside and cannot be logged into. Only a power cycle clears it. Three contributing causes: - MemoryCache had a fixed 1000-entry ceiling. Entries are parsed API payloads of tens of KB, so one ceiling cannot serve both a 512MB Zero 2 W and an 8GB Pi 5. Now scaled from MemTotal (150 entries at <=1GB, 1500 at >=8GB), overridable with LEDMATRIX_CACHE_MAX_ENTRIES. - requirements_are_satisfied() returned False for any requirement with extras, so a plugin depending on python-socketio[client] re-ran pip on every single start: ~8s, a network dependency, and a 100-200MB spike at the least convenient moment. During a restart loop it repeats for each restart. Extras are now resolved one level deep against installed metadata, keeping the conservative "anything unverifiable falls through to pip" contract. - ledmatrix.service had no memory ceiling. MemoryMax=85% expressed as a percentage so one unit file suits every board. Note this needs the memory cgroup controller, which Pi firmware disables by default; first_time_install.sh now adds cgroup_enable=memory to cmdline.txt, and the unit file documents how to verify it took effect. first_time_install.sh also enables persistent journald storage (capped at 64M). Default storage is volatile, so every reboot destroys the logs that would explain why the board rebooted. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Documents the memory ceiling on small boards and, more usefully, what running into it actually looks like: sshd accepting connections and closing them before the banner, the web UI still responding normally, clean ping, a dark panel, and a wrong clock after the next boot. None of those read as "out of memory", which makes the failure hard to identify from the symptoms. Cross-referenced from SSH_UNAVAILABLE_AFTER_INSTALL.md, since "I can't SSH in any more" is how most people will first meet this. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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📝 WalkthroughWalkthroughThe pull request adds low-memory support for Raspberry Pi boards through RAM-aware caching, memory cgroups, service limits, persistent journald storage, and troubleshooting guidance. It also repairs persisted plugin health state and validates nested package extras. ChangesLow-memory board support
Plugin state and dependency validation
Estimated code review effort: 3 (Moderate) | ~25 minutes Merge Risk: 🟡 Moderate · up to This PR improves restart and memory behavior, but malformed persisted health data can still prevent the display service from starting, while cache limits are delayed and log persistence may not take effect. These correctness and operational risks should be fixed or explicitly accepted before merge. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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| Metric | Results |
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| Complexity | 53 |
| Duplication | 0 |
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Inline comments:
In `@docs/LOW_MEMORY_BOARDS.md`:
- Around line 73-77: Update the systemd override example in LOW_MEMORY_BOARDS.md
to include steps running systemctl daemon-reload followed by restarting the
ledmatrix service, so the new LEDMATRIX_CACHE_MAX_ENTRIES setting is applied.
- Around line 59-60: Update the low-memory board instructions to tell users to
edit the active kernel command-line file: use /boot/firmware/cmdline.txt when
present, otherwise use /boot/cmdline.txt, while preserving the requirement to
keep the command line on a single line.
In `@docs/SSH_UNAVAILABLE_AFTER_INSTALL.md`:
- Around line 23-36: Update the document’s final summary to include memory
exhaustion as a possible cause of SSH failure, state that physical power cycling
is required for recovery, and link to LOW_MEMORY_BOARDS.md alongside the
existing AP-mode recovery guidance.
- Around line 29-31: Update the fenced code block containing the SSH error
output to include a text or console language identifier, resolving markdownlint
rule MD040 without changing the displayed error.
In `@first_time_install.sh`:
- Around line 1696-1705: Update the cgroup parameter check in the SKIP_PERF
configuration block to validate cgroup_enable=memory and cgroup_memory=1
independently. Append whichever required parameter is missing to CMDLINE_FILE,
while retaining the backup, status messages, and reboot-required behavior.
- Around line 1712-1725: The journald setup branch must not use /var/log/journal
contents as evidence that the desired configuration is active. Update this block
to inspect effective journald configuration or ensure the managed
persistent-storage drop-in is installed, while preserving any explicitly
configured user limits such as SystemMaxUse; restart journald only when the
managed configuration needs to be applied.
In `@src/cache_manager.py`:
- Around line 87-89: Update MemoryCache.set() to enforce max_size synchronously
on every write by evicting excess entries while holding the cache lock, rather
than relying on _cleanup_memory_cache(). Preserve normal insertion behavior
while ensuring the cache never remains above the configured ceiling after an
insertion.
In `@src/plugin_system/plugin_health.py`:
- Around line 67-79: Validate cached health-state dictionaries in the
health-state loading method before returning them, including required keys,
expected value types, and allowed circuit_state values. If any check fails, log
the malformed entry and fall back to rebuilding the default state; preserve the
existing return path only for fully valid dictionaries.
In `@src/plugin_system/plugin_loader.py`:
- Around line 90-96: Update requirements_are_satisfied() to recursively validate
each gated dependency’s requested extras, tracking visited (distribution,
extras) pairs to prevent cycles or duplicate traversal. Preserve the existing
distribution version checks, and return false when any dependency required by an
extra is missing or incompatible so pip is not skipped.
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Nine CodeRabbit findings, five in code. **Health state (the one that matters).** The non-dict guard did not cover a dict missing fields the callers index directly, which is the shape actually seen in the wild: a record carrying only circuit_state produced `plugin clock-simple operation failed: 'circuit_state'` about fifty times a minute with the panel frozen. The record is now completed against the defaults per field rather than trusted or discarded wholesale. Per field matters: a first pass rejected any incomplete record outright, which reset a tripped breaker and real failure counts to healthy because one optional field was absent -- an existing test caught it. Values of the wrong type (a counter persisted as a string, an unknown circuit_state) fall back individually, valid neighbours survive, and newer fields the schema has grown since (degraded, degraded_reason) are carried through untouched. **Cache ceiling.** MemoryCache.set() accepted entries without bound between cleanup sweeps, which run every 300s by default, so a burst could take the cache far past max_size -- the unbounded growth the limit exists to stop. Eviction now runs under the same lock on every write, sharing one helper with the periodic sweep so the two cannot drift. **Installer, cgroups.** Only cgroup_enable=memory was checked, so a board carrying that without cgroup_memory=1 reported success and got no change, leaving MemoryMax= inert. Each parameter is now checked and appended independently; verified against all four combinations, single line preserved. **Installer, journald.** Persistence was inferred from /var/log/journal being non-empty, which proves neither Storage=persistent nor a size cap -- the directory survives a switch back to volatile. The effective configuration is read instead (systemd-analyze cat-config, falling back to the conf files), and an explicitly configured SystemMaxUse is preserved rather than overwritten. Verified across volatile, persistent-without-cap, persistent-with-user-cap, cap-without-storage, and commented-only configs. **Dependency extras.** _extras_are_satisfied stopped at one level, so a gated dependency that itself requests an extra (requests[socks]) passed on the base distribution's version while the extra's own dependency was missing, and pip was skipped. It now recurses, with a visited (distribution, extras) set so a cycle terminates. Docs: both kernel command-line paths documented (the installer falls back to /boot/cmdline.txt), daemon-reload and restart added after the systemd override example, memory exhaustion added to the SSH summary with its power-cycle-only recovery, and a language on the fenced block for MD040. Tests: five for the health-state repair including the exact wild shape and that record_failure/record_success no longer raise against it, and one for the cache ceiling. Both mutation-checked. Full suite 2927 passed, with the one pre-existing tmpfs failure that also fails on main. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01STMbQE4YctTacQXfbYqKuW
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Inline comments:
In `@first_time_install.sh`:
- Around line 1743-1758: Update the journald configuration flow around the
ledmatrix-persistent.conf write to re-read the effective journald settings
afterward, verify that Storage=persistent is active, and report failure when
persistence is not effective. Keep the existing configuration generation and cap
handling unchanged.
In `@src/plugin_system/plugin_health.py`:
- Around line 139-146: Update the validation logic around the timestamp and
circuit-state branches: reject bool values in _TIMESTAMP_FIELDS while continuing
to accept None, int, and float, and require circuit_state to be a string before
checking membership in CircuitState values so unhashable inputs are rebuilt
rather than raising. Add regression coverage for an unhashable circuit_state and
boolean circuit_opened_time.
In `@test/test_plugin_health.py`:
- Around line 163-167: Update
test_recording_against_a_repaired_state_does_not_raise to seed _tracker_reading
with a non-empty record that omits circuit_state, while retaining the
record_failure and record_success calls to exercise the repaired-state behavior.
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Second review round; all three findings were valid and two were bugs in the
repair added last commit.
The repair could raise out of itself. An unhashable circuit_state (a list or
dict on disk) hit `value in {...}` and raised TypeError -- from the code
whose whole job is to stop a malformed record crashing the caller. It now
requires a str before the membership test.
bool is a subclass of int, so True passed the timestamp check and then
compared as 1.0: enough to expire a cooldown the instant the breaker opened,
while False would stop the elapsed check firing at all. Timestamps now
exclude bool explicitly.
The regression test for the original crash was seeded with a record that
*contained* circuit_state, so it passed against the old raw-return behaviour
too -- the counters are read with .get(), so circuit_state is the only field
whose absence used to raise. Reseeded to omit it, and it now fails against
raw-return as intended.
journald: drop-ins apply in lexical order, so a local file sorting after
ledmatrix-persistent.conf still wins and writing ours proves nothing. The
effective Storage is re-read afterwards and a warning naming the diagnostic
command is printed if persistence is still not active, rather than reporting
a success that was not verified.
Full suite 2934 passed, same single pre-existing tmpfs failure.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01STMbQE4YctTacQXfbYqKuW
This was referenced Aug 20, 2026
ChuckBuilds
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that referenced
this pull request
Aug 25, 2026
* fix(plugins): cap the per-plugin state transition history
PluginStateManager recorded every state transition in a per-plugin list
and never trimmed it. The only code that removed entries was
clear_state(), called solely from PluginManager.unload_plugin(), so a
plugin that stays loaded -- normal operation -- never released one.
The list is written on the hot scheduling path. Every update cycle
appends twice: _reserve_for_update() sets RUNNING and _finish() sets
ENABLED back again. At the default 60s update interval that is 2,880
entries per plugin per day, and nothing reads them -- get_state_info()
only takes their len(). Pure dead weight.
Measured against the unpatched class, ten plugins on a 60s interval:
sim uptime history entries heap growth
1 day 28,810 7.7 MB
7 days 201,610 53.9 MB
30 days 864,010 230.9 MB (still climbing)
With the cap it is flat at 2,000 entries / 0.5 MB from day one.
On a 1 GB board 231 MB of garbage is fatal on its own, and the failure
is not a clean OOM: once MemAvailable falls far enough fork() starts
returning ENOMEM, so sshd accepts connections and closes them before its
banner while the kernel still answers pings. The board looks like a
hardware fault and needs a power cycle. Same family as the ceilings
added in #464.
Retain the most recent 200 transitions per plugin in a deque and let the
rest age out. state_history_count is surfaced through the web API, so
the lifetime total is tracked separately rather than plateauing at the
cap. get_state_history() now returns a copy under the lock; it was
handing out the manager's own list, which a caller could mutate.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
* fix(plugins): copy history entries out, lock clear_state
Review follow-ups on the transition history.
get_state_history() copied only the outer list, so a caller holding a
returned transition could rewrite the manager's record of what happened
-- which contradicted the defensive-copy guarantee in its own docstring.
Copy each entry too. Every value in a transition is immutable, so a
shallow copy per entry is enough. test_get_state_history_entries_are_copies
pins it; without the change it fails with 'tampered' == 'enabled'.
clear_state() mutated five shared dicts without holding _lock, while
every other mutator takes it. A concurrent set_state() could interleave
and leave a plugin with history but no state. Drop the five as one unit.
This does not close the wider unload-vs-worker race, which lives in
PluginManager.unload_plugin() and predates this change: an update worker
still in flight can call set_state() after clear_state() returns and
recreate the entry. Serialising that needs the per-plugin lock held
across worker join in unload_plugin(), which is a separate change.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
---------
Co-authored-by: Claude Opus 5 <noreply@anthropic.com>
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Summary
Fixes an unattended failure mode on low-memory boards where the Pi becomes
completely unreachable — SSH refuses connections, the panel goes dark — while
still answering pings and serving the web UI, so it looks healthy from outside.
Only a power cycle clears it. Diagnosed on a 1GB Pi 3B+; it reproduced twice,
about 90 minutes after each boot.
What actually happens
The display process settles near 600MB RSS of 905MB usable. When the remaining
headroom runs out,
fork()starts failing, and since almost anything needs anew process, the symptoms do not read as "out of memory":
sshdaccepts the TCP connection and closes it before sending its banner (itforks a session per connection)
fake-hwclock's periodic save stops running, so the clock is wrong after thenext boot
Changes
Service resilience
PluginHealthTracker._load_health_state()returned the cached value verbatim.A non-dict entry makes every caller raise
AttributeError: 'list' object has no attribute 'get'duringDisplayController.__init__, so the process diesbefore the display loop starts — an unattended restart loop that survives
reboots, because the bad entry is persisted. Observed in the field. Non-dict
entries are now discarded with a warning and defaults rebuilt.
ledmatrix.serviceusedRestart=on-failure, so an exit with status 0 leftthe unit stopped and the panel dark indefinitely. Now
Restart=always.ledmatrix-wifi-monitor.serviceusedStandardOutput=syslog, which systemdhas marked obsolete and rewrites on every load.
Memory
MemoryCachehad a fixed 1000-entry ceiling. Entries are parsed API payloadsof tens of KB, so one ceiling cannot serve both a 512MB Zero 2 W and an 8GB
Pi 5. Now scaled from
MemTotal— 150 entries at <=1GB, 1500 at >=8GB —overridable with
LEDMATRIX_CACHE_MAX_ENTRIES.requirements_are_satisfied()returned False for any requirement withextras, so a plugin depending on
python-socketio[client]re-ran pip on everysingle start: ~8s, a network dependency, and a 100-200MB spike — repeated for
each restart during a crash loop. Extras are now resolved one level deep
against installed metadata, keeping the conservative "anything unverifiable
falls through to pip" contract.
MemoryMax=85%, as a percentage so one unit file suits every board. Thisneeds the memory cgroup controller, which Pi firmware disables by default —
first_time_install.shnow addscgroup_enable=memorytocmdline.txt, andthe unit documents how to verify it took effect. Without it systemd accepts
the setting and silently ignores it.
first_time_install.shalso enables persistent journald storage (capped at64M). Default storage is volatile, so every reboot destroys the logs that
would explain the reboot.
Docs —
docs/LOW_MEMORY_BOARDS.md, linked from the docs index andcross-referenced from
SSH_UNAVAILABLE_AFTER_INSTALL.md, since "I can't SSH inany more" is how most people will meet this.
Note on scope
The memory ceiling is a safety net, not a cure. On a 1GB board this workload
genuinely wants ~67% of RAM, so any ceiling safe enough to protect the system is
one it may reach. It converts "the board becomes unreachable until someone pulls
the plug" into "one service restarts". Running fewer plugins is the real remedy,
which is what the doc says.
Testing
main: identical failure sets (2777 passing; 84pre-existing failures are Windows path/file-locking issues, unrelated). Failure
lists were diffed rather than compared by count — one run showed 85 vs 84, which
was a flaky test.
systemd-analyze verifyon the patched unit with placeholders expanded, on thePi — clean.
bash -nonfirst_time_install.sh.resolves
python-socketio[client]torequests+websocket-client, finds bothinstalled, returns satisfied.
previously used 1000.
Summary by CodeRabbit