WAPFILENAME=/swap.img
MEMSIZE=`cat /proc/meminfo | grep MemTotal | awk '{print $2}'`

if [ $MEMSIZE -lt 2097152 ]; then
  SIZE=$(($MEMSIZE * 2))k
elif [ $MEMSIZE -lt 8388608 ]; then
  SIZE=${MEMSIZE}k
elif [ $MEMSIZE -lt 67108864 ]; then
  SIZE=$(($MEMSIZE / 2))k
else
  SIZE=4194304k
fi

fallocate -l $SIZE $SWAPFILENAME && mkswap $SWAPFILENAME && swapon $SWAPFILENAME