Comment 5 for bug 1270913

PS just had a thought and this is from chromium OS

https://chromium.googlesource.com/chromiumos/platform/init/+/factory-3536.B/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 "<email address hidden>"
# 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=$2, for a savings of about 3ms on an Alex.
  ram=$(awk '/MemTotal/ { print $2; }' < /proc/meminfo)
  [ "$ram" = "" ] && logger -t "$UPSTART_JOB" "could not get MemTotal"
  # compute fraction of total RAM used for low-mem margin. The fraction is
  # given in bips. A "bip" or "basis point" is 1/100 of 1%. This unit is
  # typically used in finance and in low-memory margin calculations.
  MARGIN_BIPS=520
  margin=$(($ram / 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"
  if [ ! -f $SWAP_ENABLE_FILE ]; then
    metrics_client Platform.CompressedSwapSize 0 $HIST_ARGS
    exit 0
  fi
  # Load zram module. Ignore failure (it could be compiled in the kernel).
  modprobe zram || logger -t "$UPSTART_JOB" "modprobe zram failed (compiled?)"
  # Allocate zram (compressed ram disk) for swap.
  # Default for uncompressed size is 1.5 of total memory.
  # Override with content of .swap_enabled (in Mb).
  # 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
    ZRAM_SIZE_KB=$(awk '/MemTotal/ { print $2 * 3 / 2 }' /proc/meminfo)
  elif [ "$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 $HIST_ARGS
    exit 1
  else
    ZRAM_SIZE_KB=$(($REQUESTED_SIZE_MB * 1024))
  fi
  logger -t "$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 "$UPSTART_JOB" "mkswap /dev/zram0 failed"
  swapon /dev/zram0 || logger -t "$UPSTART_JOB" "swapon /dev/zram0 failed"
  metrics_client Platform.CompressedSwapSize \
                $(($ZRAM_SIZE_KB / 1024)) $HIST_ARGS
end script