#!/usr/bin/env bash
# Run a heavy command on the 8 GB Pi with a memory guard. Raspberry Pi OS boots with cgroup_disable=memory, so
# systemd MemoryMax cannot be used; instead the command runs in its own process group and is stopped (TERM, then
# KILL) as soon as the system's MemAvailable drops below MIN_FREE_MB -- before the kernel OOM killer would pick
# victims such as the desktop session. Prints the peak resident memory of the command's process tree.
#   MIN_FREE_MB=1200 bash scripts/pi_run.sh <command...>
set -uo pipefail
MIN_FREE_MB=${MIN_FREE_MB:-1200}
setsid "$@" &
pid=$!
peak=0
tripped=0
tree_rss() {  # kB, summed over the process group
  ps -o rss= -g "$pid" 2>/dev/null | awk '{s+=$1} END {print s+0}'
}
while kill -0 "$pid" 2>/dev/null; do
  rss=$(tree_rss); (( rss > peak )) && peak=$rss
  avail=$(awk '/^MemAvailable:/ {print int($2/1024)}' /proc/meminfo)
  if (( avail < MIN_FREE_MB )); then
    echo "pi_run: MemAvailable ${avail} MiB < ${MIN_FREE_MB} MiB -- stopping the job (process group $pid)" >&2
    kill -TERM -- "-$pid" 2>/dev/null; sleep 5; kill -KILL -- "-$pid" 2>/dev/null
    tripped=1
    break
  fi
  sleep 1
done
wait "$pid"; rc=$?
(( tripped )) && rc=137
echo "pi_run: exit $rc, peak RSS $((peak / 1024)) MiB, guard ${MIN_FREE_MB} MiB free" >&2
exit $rc