Comment 3 for bug 1270913

https://www.kernel.org/doc/Documentation/blockdev/zram.txt

"num_devices parameter is optional and tells zram how many devices should be
pre-created. Default: 1"

The whole first procedure is a question to why and completely fails to check previous devices or modprobe zram services:-
*******************************************************************
# load dependency modules
if grep ZRAM=m /boot/config-$(uname -r)
  NRDEVICES=$(grep -c ^processor /proc/cpuinfo | sed 's/^0$/1/')
  if modinfo zram | grep -q ' zram_num_devices:' 2>/dev/null; then
    MODPROBE_ARGS="zram_num_devices=${NRDEVICES}"
  elif modinfo zram | grep -q ' num_devices:' 2>/dev/null; then
    MODPROBE_ARGS="num_devices=${NRDEVICES}"
  else
    exit 1
  fi
  modprobe zram $MODPROBE_ARGS
fi
*****************************************************************
zram can be easily checked to see if it has a sys class

        ZRAM_SYS_DIR='/sys/class/zram-control'
        if [ ! -d "${ZRAM_SYS_DIR}" ]; then

if not then modprobe zram will create it.
So after a modprobe zram all you have to do is create first device /dev/zram0
As cat /sys/class/zram-control/hot_add will always contain the next device number and will already contain '1'

After that

      RAM_DEV=$(cat /sys/class/zram-control/hot_add)
      echo ${COMP_ALG_SWAP} > /sys/block/zram${RAM_DEV}/comp_algorithm
      echo ${mem} > /sys/block/zram${RAM_DEV}/disksize
      mkswap /dev/zram${RAM_DEV}
      swapon -p ${SWAP_PRI} /dev/zram${RAM_DEV}
is all that is needed as cat /sys/class/zram-control/hot_add is incremented on each addition

But then we have the questions of if a single device is automatically allocated streams for all cores why add a block device for each core?

Also zram can use all crypto listed in proc/crypto but its hard coded.
Same for swap priority & size setting.

There is little correlation in the methods used in zram-config & https://www.kernel.org/doc/Documentation/blockdev/zram.txt and maybe someone should ask why?