main/postmarketos-zram: new aport

This is meant to replace zram-init. It's much simpler, since it only
sets up zram swap and doesn't try to do all the things that zram-init
does. This also lets us add additional logic, such as selecting
different default algorithms based on the runtime CPU arch and
conditionally applying sysctl settings that might be inappropriate when
*not* using zram swap.

To create zramstart, I took the zram-configurator, which reads config
from deviceinfo vars, and extended it to create the zram swap device.

zramstart and zramstop were inspired by what Fedora does. The sysctl
config is from the work done here:
https://source.puri.sm/Librem5/librem5-base/-/merge_requests/381

Signed-off-by: Clayton Craft <craftyguy@postmarketos.org>
Part-of: <https://gitlab.postmarketos.org/postmarketOS/pmaports/-/merge_requests/7754>

main/postmarketos-zram/APKBUILD

@@ -0,0 +1,32 @@
+maintainer="Clayton Craft <clayton@craftyguy.net>"
+pkgname=postmarketos-zram
+pkgver=1
+pkgrel=0
+pkgdesc="zram swap configuration for postmarketOS"
+url="https://postmarketos.org"
+arch="noarch"
+license="GPL-3.0-or-later"
+depends="util-linux-misc"
+subpackages="$pkgname-openrc $pkgname-systemd"
+replaces="postmarketos-base"
+options="!check"
+source="
+	postmarketos-zram-swap.initd
+	postmarketos-zram-swap.service
+	zramstart
+	zramstop
+"
+
+package() {
+	install -Dm755 zramstart -t "$pkgdir"/usr/bin
+	install -Dm755 zramstop -t "$pkgdir"/usr/bin
+	install -Dm755 postmarketos-zram-swap.initd "$pkgdir"/etc/init.d/postmarketos-zram-swap
+	install -Dm644 postmarketos-zram-swap.service -t "$pkgdir"/usr/lib/systemd/system
+}
+
+sha512sums="
+ca91be78a47c00f40f3e645f79a72b2cd7ba3f080e2feb256998bb121f64c0394041f2ed822ad307ac36e86398b8175b3284dc5097a7017947e520a304b0a37d  postmarketos-zram-swap.initd
+5c1787bc2d597726113aaf3ea59229b5a56b8fc3446c78406a202e163a0b37ac564a87b2acc1c1f1a7dcdc18ff863c45e13aa687b93fa537c5ef000b9e8d6d19  postmarketos-zram-swap.service
+798e162f0393621144bfef843fa2f21f9cdfaaa4cd07d4d8b63499f8c3db27d6b9cbb901b43459e5378bd2bb6905f1e371ff915b8e439908944e8030eee7b48e  zramstart
+a70d2bcb26c1af42a71811a1c1cd2984808f5ce09d7af52b26824cf5c15c8a9c819691fc6290cf3028226fca39f6e7a495546c5573c582a14d5a8c7c65dbfe3e  zramstop
+"

main/postmarketos-zram/postmarketos-zram-swap.initd

@@ -0,0 +1,25 @@
+#!/sbin/openrc-run
+# SPDX-License-Identifier: GPL-2.0-only
+
+depend() {
+	need localmount
+	after bootmisc modules
+	provide swap
+}
+
+start() {
+	ebegin "Starting zram swap"
+	if [ ! -f /usr/share/misc/source_deviceinfo ]; then
+		eend 1 "deviceinfo not found"
+		return 1
+	fi
+
+	zramstart
+	eend $?
+}
+
+stop() {
+	ebegin "Stopping zram swap"
+	zramstop
+	eend $?
+}

main/postmarketos-zram/postmarketos-zram-swap.service

@@ -0,0 +1,15 @@
+[Unit]
+Description=Enable compressed swap in memory using zram
+DefaultDependencies=no
+Before=swap.target
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+TimeoutStartSec=30sec
+ExecCondition=sh -c '. /usr/share/misc/source_deviceinfo'
+ExecStart=/usr/bin/zramstart
+ExecStop=/usr/bin/zramstop
+
+[Install]
+WantedBy=swap.target

main/postmarketos-zram/zramstart

@@ -0,0 +1,71 @@
+#!/bin/sh
+# shellcheck disable=SC3043
+
+set -e
+
+# shellcheck disable=SC1091
+. /usr/share/misc/source_deviceinfo
+
+get_size() {
+        # Size defaults to:
+        # - 75% of RAM for devices with 2GB of RAM or less
+        # - 50% of RAM for devices with between 2GB and 6GB of RAM
+        # - 25% of RAM for devices with greater 6GB of RAM
+        # This is loosely based on some data here:
+        # https://gitlab.postmarketos.org/postmarketOS/pmaports/-/merge_requests/3752#note_1229631449
+
+        local mem_size_mb size_pct
+        mem_size_mb="$(LC_ALL=C free -m | awk '/^Mem:/{print $2}')"
+
+        if [ "$mem_size_mb" -le 2048 ]; then
+                size_pct=75
+        elif [ "$mem_size_mb" -gt 6144 ]; then
+                size_pct=25
+        else
+                size_pct=50
+        fi
+
+        # Allow overriding the size as a percentage of RAM using a deviceinfo var, or
+        # disabling it completely
+        if [ -n "$deviceinfo_zram_swap_pct" ]; then
+                # 0% --> disable zram swap
+                if [ "$deviceinfo_zram_swap_pct" = "0" ]; then
+                        echo 0
+                        return
+                fi
+
+                size_pct="$deviceinfo_zram_swap_pct"
+        fi
+
+        echo $((mem_size_mb * size_pct / 100))
+}
+
+get_algo() {
+        # Default to zstd compression, and allow overriding via deviceinfo
+        # TODO: Architecture-specific defaults?
+        # TODO: Ensure deviceinfo uses valid and usable algorithm for running
+        # kernel
+        echo "${deviceinfo_zram_swap_algo:-zstd}"
+}
+
+size=$(get_size)
+algo=$(get_algo)
+
+[ "$size" -eq 0 ] && exit 0
+
+if swapon --show=NAME --noheadings | grep -q '^/dev/zram'; then
+	echo "ZRAM swap already active, skipping setup"
+	exit 0
+fi
+
+modprobe -q zram num_devices=1
+dev="$(zramctl -f -a "$algo" -s "${size}"M)"
+mkswap "$dev" >/dev/null
+swapon "$dev" >/dev/null
+
+# ZRAM-optimized sysctl settings
+sysctl -w \
+    vm.page-cluster=0 \
+    vm.swappiness=180 >/dev/null
+
+echo "ZRAM swap device $dev activated using $algo and size $size MB"

main/postmarketos-zram/zramstop

@@ -0,0 +1,6 @@
+#!/bin/sh
+
+for i in $(grep '^/dev/zram' /proc/swaps | awk '{ print $1 }'); do
+        swapoff "$i" && zramctl --reset "$i"
+        echo "Stopped ZRAM swap device $i"
+done