rpi-zram-service: Add little systemd service to enable zram on the RPi.

* Needs to move to something more generic in time.

recipes-core/systemd/rpi-zram-service.bb

@@ -0,0 +1,30 @@
+DESCRIPTION = "Linux zram compressed in-memory swap systemd service"
+LICENSE = "MIT"
+LIC_FILES_CHKSUM = "file://${COREBASE}/LICENSE;md5=3f40d7994397109285ec7b81fdeb3b58"
+
+inherit allarch systemd
+
+PR = "r0"
+
+SRC_URI = "file://rpi-zram.service \
+           file://rpi-load-zram.sh \
+          "
+
+do_compile() {
+    :
+}
+
+
+do_install () {
+	install -d ${D}/${bindir}
+
+	install -m 0755 ${WORKDIR}/rpi-load-zram.sh ${D}/${bindir}
+	
+	install -d ${D}/${base_libdir}/systemd/system
+	install -m 0644 ${WORKDIR}/rpi-zram.service ${D}/${base_libdir}/systemd/system/
+}
+
+SYSTEMD_PACKAGES = "${PN}"
+SYSTEMD_SERVICE_${PN} = "rpi-zram.service"
+
+FILES_${PN} += "${base_libdir}/systemd"

recipes-core/systemd/rpi-zram-service/rpi-load-zram.sh

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+#!/bin/sh
+
+num_cpus=$(grep -c processor /proc/cpuinfo)
+[ "$num_cpus" != 0 ] || num_cpus=1
+
+last_cpu=$((num_cpus - 1))
+
+mem_by_cpu=$(awk -v cpus=$num_cpus '/MemTotal/ { print (($2 * 1024) / cpus) }' /proc/meminfo)
+
+if [ "$1" = "--load" ] ; then
+	echo zram: Trying to load kernel module.
+	
+	# Linux 3.2 workaround - value name changed :o.
+	# modprobe -q zram zram_num_devices=$num_cpus
+	
+	# Linux < 3.2.
+	modprobe -q zram num_devices=$num_cpus 
+
+	echo zram: Enable in-memory compressed swap of $mem_by_cpu bytes.
+	for i in $(seq 0 $last_cpu); do
+		echo $mem_by_cpu > /sys/block/zram$i/disksize
+		mkswap /dev/zram$i
+		swapon -p 100 /dev/zram$i
+	done
+fi
+
+if [ "$1" = "--unload" ] ; then
+	echo zram: Disable in-memory compressed swap.
+	for i in $(seq 0 $last_cpu); do
+		grep -q "/dev/zram$i" /proc/swaps && swapoff /dev/zram$i
+	done
+	
+	sleep 1
+	echo zram: Unload kernel module.
+	rmmod zram
+fi

recipes-core/systemd/rpi-zram-service/rpi-zram.service

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+[Unit]
+Description=Enable zram compressed in-memory swap.
+After=multi-user.target
+
+[Service]
+RemainAfterExit=yes
+ExecStart=/usr/bin/rpi-load-zram.sh --load
+ExecStop=/usr/bin/rpi-load-zram.sh --unload
+Type=oneshot
+
+[Install]
+WantedBy=multi-user.target