feat: Auto-configure zram with optimal settings

debian/pop-default-settings.postinst

@@ -90,6 +90,7 @@ X-Repolib-Default-Mirror: ${SYS_REPO}"
 
 case "$1" in
     configure)
+        systemctl enable --now pop-zram.service || echo pop-zram configure failed
         for divert in "${diverts[@]}"
         do
             source="${divert%%=*}"

debian/pop-default-settings.prerm

@@ -18,6 +18,7 @@ diverts=(
 
 case "$1" in
     remove)
+        systemctl disable pop-zram.service
         for divert in "${diverts[@]}"
         do
             source="${divert%%=*}"

etc/default/pop-zram

@@ -0,0 +1,8 @@
+# Default to 8192M as max zram block size.
+MAX_SIZE=8192
+# Amount of memory to use for zram, from 1 to 100.
+PORTION=50
+# Default to compress with zstd, which has an average compression ratio of 3.37.
+ALGO=zstd
+# Higher values encourage the kernel to be more eager to move pages to swap.
+SWAPPINESS=180

etc/sysctl.d/10-pop-default-settings.conf

@@ -1,3 +1,4 @@
 vm.swappiness = 10
+vm.watermark_boost_factor = 125
 vm.dirty_bytes = 268435456
 vm.dirty_background_bytes = 134217728

usr/bin/pop-zram-config

@@ -0,0 +1,61 @@
+#!/bin/bash
+# Copyright 2022 System76 <info@system76.com>
+# SPDX-License-Identifier: GPL-3.0-only
+
+# If a zram device already exists, ignore
+test -b /dev/zram0 && exit 0
+
+UDEV_CONF='/etc/udev/rules.d/60-pop-zram.rules'
+
+# Load user-defined variabls if a config exists
+if test -f /etc/pop-zram; then
+    export $(grep -v '^#' /etc/pop-os/zram-config | xargs)
+fi
+
+# Default to compress with zstd, which has an average compression ratio of 3.37.
+test -n ${ALGO} || ALGO=zstd
+
+# Default to 8192M as max zram block size.
+test -n ${MAX_SIZE} || MAX_SIZE=8192
+
+# Higher values encourage the kernel to be more eager to move pages to swap.
+test -n ${SWAPPINESS} || SWAPPINESS=180
+
+# Amount of memory to use for zram, from 1 to 100.
+if test -n ${PORTION}; then
+    PORTION=50
+elif ((PORTION > 100)); then
+    PORTION=100
+elif ((PORTION < 1)); then
+    PORTION=1
+fi
+
+# Number of consecutive pages to read in advance. Higher values increase compression
+# for zram devices, but at the cost of significantly reduced IOPS and higher latency.
+# It is highly recommended to use 0 for zstd; and 1 for speedier algorithms.
+test -n ${PAGE_CLUSTERS} || PAGE_CLUSTERS=$(test zstd = ${ALGO} && echo 0 || echo 1)
+
+# Total amount of memory accessible to the OS.
+TOTAL=$(awk -v p=${PORTION} '/MemTotal/ {printf "%.0f", p * $2 / 102400}' /proc/meminfo)
+
+# The recommended size is `max(mem_total / 2, 8GB)`.
+SIZE=$(((TOTAL > MAX_SIZE)) && echo ${MAX_SIZE} || echo ${TOTAL})
+
+# Creates the udev rule for the block device at `${UDEV_CONF}`.
+UDEV_RULE='KERNEL=="zram0", SUBSYSTEM=="block", DRIVER=="", ACTION=="add", ATTR{initstate}=="0", ATTR{comp_algorithm}="{{ALGO}}", ATTR{disksize}="{{SIZE}}", RUN+="/sbin/mkfs.ext4 -O ^has_journal -L $name $env{DEVNAME}"'
+echo ${UDEV_RULE} | sed -e "s/{{SIZE}}/${SIZE}M/g" -e "s/{{ALGO}}/${ALGO}/g" > ${UDEV_CONF}
+
+# Load the zram module.
+modprobe zram num_devices=1
+
+# Apply the udev rule, which creates and configures the zram device.
+udevadm control --reload-rules
+udevadm trigger
+udevadm settle
+
+# Activate the zram device with a priority of 1000.
+# This device should have a higher priority than disk-based swap.
+swapon -p 1000 /dev/zram0
+
+# Apply optimal sysctl values for the zram environment.
+sysctl -w "vm.page-cluster=${PAGE_CLUSTERS}" "vm.swappiness=${SWAPPINESS}"

usr/lib/systemd/system/pop-zram.service

@@ -0,0 +1,9 @@
+[Unit]
+Description=Auto-configure and enable zram on Pop
+
+[Service]
+Type=oneshot
+ExecStart=/usr/bin/pop-zram-config
+
+[Install]
+WantedBy=multi-user.target