Initial code push

README.md

@@ -1,2 +1,32 @@
 # zram-swap
-zram swap setup + teardown with systemd unit & /etd/default configuration
+Simple zram swap setup + teardown script with systemd unit & /etc/default configuration
+
+https://github.com/foundObjects/zram-swap
+
+### Installation
+
+```
+git clone https://github.com/foundObjects/zram-swap.git
+cd zram-swap && sudo bash install.sh
+```
+
+### Usage
+
+zram-swap.service will be started automatically during boot.
+
+The default allocation creates a zram device that should use around half of physical memory when completely full.
+
+Edit `/etc/default/zram-swap-service` if you'd like to change compression algorithms or swap allocation and then restart zram-swap with `systemctl restart zram-swap.service`.
+
+Run `zramctl` during use to monitor swap compression and real memory usage.
+
+### Debugging
+
+Either start zram-swap.sh with `bash -x zram-swap.sh` or `./zram-swap.sh -x (start|stop)` to see what's going wrong.
+
+To dump the full execution trace during service start/stop edit  /etc/systemd/systemd/zram-swap.service and add -x to the following two lines:
+
+```
+ExecStart=/usr/local/sbin/zram-swap.sh -x init
+ExecStop=/usr/local/sbin/zram-swap.sh -x  end
+```

install.sh

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+#!/usr/bin/env bash
+
+[[ "$EUID" == 0 ]] || { echo "This script requires root." && exit 1; }
+set -ex
+
+if systemctl -q is-active zram-swap.service; then
+  systemctl stop zram-swap.service
+fi
+
+install -o root zram-swap.sh /usr/local/sbin/zram-swap.sh
+install -o root zram-swap-service /etc/default/zram-swap-service
+install -o root zram-swap.service /etc/systemd/system/zram-swap.service
+
+systemctl daemon-reload
+systemctl enable zram-swap.service
+systemctl start zram-swap.service

zram-swap-service

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+# portion of real ram to use as zram swap (expression: "1/2", "0.5", etc)
+_zram_fraction="1/2"
+
+# compression algorithm to employ (lzo, lz4, zstd, lzo-rle)
+_zram_algorithm="lz4"
+
+# set expected compression ratio based on algorithm; this is a rough estimate
+# set this by hand if you use an algorithm other than lzo/lz4/zstd
+#_comp_factor="2.5"
+#
+# defaults:
+#case $_zram_algorithm in
+#	lzo*|zstd)
+#		_comp_factor="3"
+#		;;
+#	lz4)
+#		_comp_factor="2.5"
+#		;;
+#	*)
+#		_comp_factor="2"
+#		;;
+#esac

zram-swap.service

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+[Unit]
+Description=zram swap service
+Requires=systemd-modules-load.service local-fs.target
+
+[Service]
+Type=oneshot
+ExecStart=/usr/local/sbin/zram-swap.sh init
+ExecStop=/usr/local/sbin/zram-swap.sh end
+RemainAfterExit=True
+
+[Install]
+WantedBy=sysinit.target
+#RequiredBy=

zram-swap.sh

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+#!/bin/bash
+# source: https://github.com/foundObjects/zram-swap
+
+[[ "$EUID" == "0" ]] || { echo "This script requires root." && exit 1; }
+set -eo pipefail
+
+# parse debug flag early so we can trace everything
+[[ "$1" == "-x" ]] && { shift && set -x; } >&/dev/null
+
+# set sane defaults, see /etc/default/zram-swap-service for explanations
+_zram_fraction="1/2"
+_zram_algorithm="lz4"
+_comp_factor=''
+
+# load user config
+[[ -f /etc/default/zram-swap-service ]] &&
+  source /etc/default/zram-swap-service
+
+# set expected compression ratio based on algorithm; this is a rough estimate
+# skip if already set in user config
+if [[ -z "$_comp_factor" ]]; then
+  case $_zram_algorithm in
+    lzo* | zstd) _comp_factor="3" ;;
+    lz4) _comp_factor="2.5" ;;
+    *) _comp_factor="2" ;;
+  esac
+fi
+
+# main script:
+_main() {
+  if ! modprobe zram; then
+    err "Failed to load zram module, exiting"
+    return 1
+  fi
+
+  case "$1" in
+    # a little magic to quietly set -u after testing our last expected empty variable
+    # matches every case, runs set -u without logging to the trace and then continues matching
+    *) { set -u; } 2>/dev/null ;;&
+    "init" | "start")
+      if grep -q zram /proc/swaps; then
+        err "zram swap already in use, exiting"
+        return 1
+      fi
+      _init
+      ;;
+    "end" | "stop")
+      if ! grep -q zram /proc/swaps; then
+        err "no zram swaps to cleanup, exiting"
+        return 1
+      fi
+      _end
+      ;;
+    *)
+      echo "Usage: $0 (init|end)"
+      return 1
+      ;;
+  esac
+}
+
+# initialize swap
+_init() {
+  # Calculate memory to use for zram
+  totalmem=$(LC_ALL=C free | grep -e "^Mem:" | sed -e 's/^Mem: *//' -e 's/  *.*//')
+  mem=$(calc "$totalmem * $_comp_factor * $_zram_fraction * 1024")
+
+  # NOTE: init is a little janky; zramctl sometimes fails if we don't wait after module
+  #       load so retry a couple of times with slightly increasing delay before giving up
+  _device=''
+  for i in $(seq 3); do
+    sleep "$(calc "0.1 * $i")"
+    _device=$(zramctl -f -s "$mem" -a "$_zram_algorithm") || true
+    [[ -b "$_device" ]] && break
+  done
+
+  if [[ -b "$_device" ]]; then
+    # cleanup the device if swap setup fails
+    trap "_rem_zdev $_device" EXIT
+    mkswap "$_device"
+    swapon -p 5 "$_device"
+    trap - EXIT
+    return 0
+  else
+    err "Failed to initialize zram device"
+    return 1
+  fi
+}
+
+# end swapping and cleanup
+_end() {
+  local ret="0"
+  DEVICES=$(grep zram /proc/swaps | awk '{print $1}')
+  for d in $DEVICES; do
+    swapoff "$d"
+    if ! _rem_zdev "$d"; then
+      err "Failed to remove zram device $d"
+      ret=1
+    fi
+  done
+  return "$ret"
+}
+
+# Remove zram device with retry
+_rem_zdev() {
+  if [[ ! -b "$1" ]]; then
+    err "No zram device '$1' to remove"
+    return 1
+  fi
+  for i in $(seq 3); do
+    sleep "$(calc "0.1 * $i")"
+    zramctl -r "$1" || true
+    [[ -b "$1" ]] || break
+  done
+  if [[ -b "$1" ]]; then
+    err "Couldn't remove zram device '$1' after 3 attempts"
+    return 1
+  fi
+  return 0
+}
+
+calc() { awk "BEGIN{print $*}"; }
+#crapout() { echo "$@" >&2 && exit 1; }
+err() { echo "Err '${FUNCNAME[1]}': $*" >&2; }
+
+_main "$@"