swap.conf

# Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

description     "Setup compressed memory swap"
author          "chromium-os-dev@chromium.org"

# Set margin for low-memory notifier (for tab discarder)
# Configure and start swap if SWAP_ENABLE_FILE exists.
# SWAP_ENABLE_FILE may optionally contain the uncompressed swap size (in Mb).
# Otherwise it is set to 1.5 times total RAM.
#
# To start swap, create file /home/chronos/.swap_enabled and run "start swap"
# or reboot.  To stop swap, remove the file and reboot.

start on starting system-services

script
  SWAP_ENABLE_FILE=/home/chronos/.swap_enabled
  HIST_MIN=100
  HIST_MAX=10000
  HIST_BUCKETS=50
  HIST_ARGS="$HIST_MIN $HIST_MAX $HIST_BUCKETS"

  # Extract second field of MemTotal entry in /proc/meminfo.
  # NOTE: this could be done with "read", "case", and a function
  # that sets ram=$2, for a savings of about 3ms on an Alex.
  MEM_TOTAL=$(awk '/MemTotal/ { print $2; }' < /proc/meminfo)
  [ "$MEM_TOTAL" = "" ] && logger -t "$UPSTART_JOB" "could not get MemTotal"

  # compute fraction of total RAM used for low-mem margin.  The fraction is
  # given in bips.  A "bip" or "basis point" is 1/100 of 1%.
  MARGIN_BIPS=520
  margin=$(($MEM_TOTAL / 1000 * $MARGIN_BIPS / 10000))  # MB
  # set the margin
  echo $margin > /sys/kernel/mm/chromeos-low_mem/margin
  logger -t "$UPSTART_JOB" "setting low-mem margin to $margin MB"

  # Allocate zram (compressed ram disk) for swap.
  # SWAP_ENABLE_FILE contains the zram size in MB.
  # Empty or missing SWAP_ENABLE_FILE means use default size.
  # 0 size means do not enable zram.
  # Calculations are in Kb to avoid 32 bit overflow.

  # For security, only read first few bytes of SWAP_ENABLE_FILE.
  REQUESTED_SIZE_MB="$(head -c 4 $SWAP_ENABLE_FILE)" || :
  if [ -z "$REQUESTED_SIZE_MB" ]; then
    # Default multiplier for zram size. (Shell math is integer only.)
    ZRAM_MULTIPLIER="3 / 2"
    # On ARM CPUs graphics memory is not reclaimable, so use a smaller size.
    if arch | grep -qi arm; then ZRAM_MULTIPLIER=1; fi
    # ZRAM_MULTIPLIER may be an expression, so it MUST use the $ expansion.
    ZRAM_SIZE_KB=$((MEM_TOTAL * $ZRAM_MULTIPLIER))
  elif [ "$REQUESTED_SIZE_MB" = 0 ]; then
    metrics_client Platform.CompressedSwapSize 0 $HIST_ARGS
    exit 0
  elif [ "$REQUESTED_SIZE_MB" != 500 -a \
         "$REQUESTED_SIZE_MB" != 1000 -a \
         "$REQUESTED_SIZE_MB" != 2000 -a \
         "$REQUESTED_SIZE_MB" != 3000 -a \
         "$REQUESTED_SIZE_MB" != 4000 -a \
         "$REQUESTED_SIZE_MB" != 4500 -a \
         "$REQUESTED_SIZE_MB" != 6000 ]; then
    logger -t "$UPSTART_JOB" "invalid value $REQUESTED_SIZE_MB for swap"
    metrics_client Platform.CompressedSwapSize 0 $HIST_ARGS
    exit 1
  else
    ZRAM_SIZE_KB=$(($REQUESTED_SIZE_MB * 1024))
  fi

  # Load zram module.  Ignore failure (it could be compiled in the kernel).
  modprobe zram || logger -t "$UPSTART_JOB" "modprobe zram failed (compiled?)"

  logger -t "$UPSTART_JOB" "setting zram size to $ZRAM_SIZE_KB Kb"
  # Approximate the kilobyte to byte conversion to avoid issues
  # with 32-bit signed integer overflow.
  echo ${ZRAM_SIZE_KB}000 >/sys/block/zram0/disksize ||
      logger -t "$UPSTART_JOB" "failed to set zram size"
  mkswap /dev/zram0 || logger -t "$UPSTART_JOB" "mkswap /dev/zram0 failed"
  # Swapon may fail because of races with other programs that inspect all
  # block devices, so try several times.
  tries=0
  while [ $tries -le 10 ]; do
    swapon /dev/zram0 && break
    tries=$((tries + 1))
    logger -t "$UPSTART_JOB" "swapon /dev/zram0 failed, try $tries"
    sleep 0.1
  done

  swaptotalkb=$(awk '/SwapTotal/ { print $2 }' /proc/meminfo)
  metrics_client Platform.CompressedSwapSize \
                $((swaptotalkb / 1024)) $HIST_ARGS
end script