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ChuckBuilds 9a759ee299 perf(systemd): cap glibc malloc arenas on the display service

Measured on a live rig 2.5 hours after start:

    RSS                          1030 MB
    Private_Dirty                 988 MB
    anonymous mappings > 10 MB       23
    largest        104, 79, 66, 63, 63 MB, on 64 MB-aligned addresses
    threads                           9
    cores                             3   -> glibc ceiling = 8 x 3 = 24 arenas

23 against a ceiling of 24, all 64 MB-aligned: these are glibc's per-thread
malloc arenas, not live objects. The data the process was actually holding
accounts for perhaps 15 MB -- the widest scroll strip observed was 35,746 x 64,
about 7 MB as RGB and the same again for its numpy mirror.

It is bloat rather than a leak: sampled four times over 135 seconds, RSS sat
between 990 and 1030 MB rather than climbing. glibc gives each allocating
thread its own arena, grows them to hold peak demand, and never gives them
back. A process that builds and drops large images across several threads is
exactly the shape that produces this.

The device had 59 MB free at the time, on 1845 MB total.

MALLOC_ARENA_MAX=2 trades a little allocator concurrency for that resident
memory. It is a tuning knob rather than a fix for a defect, so the rationale
and the measurements sit next to it in the unit file, and a test asserts they
stay there -- a bare environment variable invites removal by whoever meets it
next.

Two things this is NOT, both checked rather than assumed:

- Not an OOM problem today. A grep for "oom" in the service journal returned
  24 matches, all of which were the radar logging zoom=9 and zoom=7. The kernel
  OOM killer has not fired: dmesg has zero matches.
- Not currently capped by the unit's MemoryMax=85% either. That directive is in
  this file but absent from the unit actually installed on the rig, which
  reports MemoryMax=infinity, so nothing is enforcing a ceiling there.

The saving is unmeasured on hardware: applying it needs a service restart,
which blanks the panel, so that is the user's call rather than something to do
mid-audit. If p99 frame time regresses -- it sits at 18.4 ms against a 16.7 ms
budget for 60 FPS, so there is not much headroom -- raise the value rather than
remove it.

(cherry picked from commit 446207ffbc)

2026-08-20 03:54:09 -04:00

ledmatrix-web.service

fix(systemd): wait for network connectivity before starting services (#335 )

2026-05-15 15:47:35 -04:00

ledmatrix-wifi-monitor.service

fix: keep low-memory boards reachable under load (#464 )

2026-08-19 12:28:22 -04:00

ledmatrix.service

perf(systemd): cap glibc malloc arenas on the display service

2026-08-20 03:54:09 -04:00

README.md

docs: refresh and correct stale documentation across repo (#306 )

2026-04-07 21:04:25 -04:00

README.md

Systemd Service Files

This directory contains systemd service unit files for LEDMatrix services.

Service Files

ledmatrix.service - Main LED Matrix display service
- Runs the display controller (run.py)
- Starts automatically on boot
- Runs as root for hardware access
ledmatrix-web.service - Web interface service
- Runs the web interface conditionally based on config
- Starts automatically on boot if web_display_autostart is enabled
- Uses scripts/utils/start_web_conditionally.py
ledmatrix-wifi-monitor.service - WiFi monitor daemon service
- Monitors WiFi/Ethernet connectivity
- Automatically enables/disables access point mode
- Uses scripts/utils/wifi_monitor_daemon.py

Installation

These service files are installed by the installation scripts in scripts/install/:

install_service.sh installs ledmatrix.service
install_web_service.sh installs ledmatrix-web.service
install_wifi_monitor.sh installs ledmatrix-wifi-monitor.service

Manual Installation

Important: the unit files in this directory contain __PROJECT_ROOT_DIR__ placeholders that the install scripts replace with the actual project directory at install time. Do not copy them directly to /etc/systemd/system/ — the service will fail to start with WorkingDirectory=__PROJECT_ROOT_DIR__ errors.

Always install via the helper script:
sudo ./scripts/install/install_service.sh
If you really need to do it by hand, substitute the placeholder first:
PROJECT_ROOT="$(pwd)"
sed "s|__PROJECT_ROOT_DIR__|$PROJECT_ROOT|g" systemd/ledmatrix.service \
  | sudo tee /etc/systemd/system/ledmatrix.service > /dev/null
sudo systemctl daemon-reload
sudo systemctl enable ledmatrix.service
sudo systemctl start ledmatrix.service

Service Management

# Check status
sudo systemctl status ledmatrix.service

# Start/stop/restart
sudo systemctl start ledmatrix.service
sudo systemctl stop ledmatrix.service
sudo systemctl restart ledmatrix.service

# Enable/disable autostart
sudo systemctl enable ledmatrix.service
sudo systemctl disable ledmatrix.service

# View logs
journalctl -u ledmatrix.service -f