feat: introduce a simple reclaimer

We reclaim at a constant rate and skip if psi is over threshold.

Signed-off-by: greatbridf <greatbridf@icloud.com>

reclaimer.sh

@@ -0,0 +1,165 @@
+#!/bin/bash
+
+set -euo pipefail
+
+size=1M
+threshold=100
+interval=1
+debug=
+
+usage() {
+	cat <<EOF
+Usage: $0 [OPTIONS]
+
+Reclaim memory at fixed interval
+
+Options:
+	-s <size>		Memory to reclaim in one run. Available units: K, M
+				[default: $size]
+	-t <threshold>		PSI threshold to continue reclaiming.
+				[default: $threshold]
+	-i <interval>		Interval between reclaims in seconds.
+				[default: $interval]
+	-d			Enable debug output.
+				[default: no]
+	-h			Show this message.
+EOF
+	exit "$1"
+}
+
+log() {
+	printf "[%s] %5s: %s\n" "$(date +%F\ %T)" "$1" "$2" >&2
+}
+
+log_debug() {
+	log "DEBUG" "$1"
+}
+
+log_info() {
+	log "INFO" "$1"
+}
+
+log_warn() {
+	log "WARN" "$1"
+}
+
+log_fatal() {
+	log "FATAL" "$1"
+}
+
+die() {
+	log_fatal "$1"
+	exit 1
+}
+
+readpsi() {
+	psi_path="/proc/pressure/memory"
+	head -n 1 "$psi_path" | awk -F= '{ print $5 }'
+}
+
+init_reclaim_states() {
+	last_psi="$(readpsi)"
+	psi="$last_psi"
+
+	size_kb=
+	# Convert size into KBs
+	case "$size" in
+		[0-9]*M|[0-9]*m)
+			size_kb="$(echo "$size" | tr -d mM)"
+			size_kb="$((size_kb * 1024))"
+			;;
+		[0-9]*K|[0-9]*k)
+			size_kb="$(echo "$size" | tr -d kK)"
+			;;
+		*)
+			die "invalid size format: $size"
+			;;
+	esac
+
+	# Scale PSI threshold by interval
+	threshold="$((threshold * interval))"
+
+	log_info "reclaim params:"
+	log_info "size=$size threshold=$threshold interval=$interval"
+}
+
+update_states() {
+	last_psi="$psi"
+	psi="$(readpsi)"
+
+	delta="$((psi - last_psi))"
+}
+
+skip_reclaim() {
+	log_info "reclaim skipped for $1"
+}
+
+should_reclaim() {
+	if [[ "$delta" -gt "$threshold" ]]; then
+		skip_reclaim "high pressure: $delta > $threshold over the last ${interval}s"
+		return 1
+	fi
+
+	return 0
+}
+
+reclaim() {
+	cgpath="/sys/fs/cgroup"
+	echo "${size_kb}K" > "$cgpath/memory.reclaim"
+}
+
+dump_reclaim_args() {
+	log_debug "last_psi=$last_psi psi=$psi delta=$delta"
+}
+
+dump_memusage() {
+	NL=$'\n'
+	_usage="$NL$(free -h)$NL"
+
+	log_debug "memusage: $_usage"
+}
+
+wait_for_next_run() {
+	sleep "$interval"
+}
+
+reclaim_run() {
+	update_states
+
+	[ -n "$debug" ] && dump_reclaim_args
+
+	if ! should_reclaim; then
+		return
+	fi
+
+	if ! reclaim; then
+		log_warn "unable to reclaim, status=$?"
+		return
+	fi
+
+	log_info "reclaimed memory ${size_kb}K"
+
+	[ -n "$debug" ] && dump_memusage
+
+	return
+}
+
+while getopts "s:t:i:dh" arg; do
+	case "$arg" in
+		s) size="$OPTARG" ;;
+		t) threshold="$OPTARG" ;;
+		i) interval="$OPTARG" ;;
+		d) debug=y ;;
+		h) usage 0 ;;
+		?) usage 1 ;;
+	esac
+done
+
+shift $((OPTIND - 1))
+
+init_reclaim_states
+
+while true; do
+	reclaim_run
+	wait_for_next_run
+done