Hi, 
If I understand it correctly zswap might still rely on an additional swap device
zswap
[…]instead of moving memory pages to a swap device when they are to be swapped out, zswap performs their compression and then stores them into a memory pool dynamically allocated in the system RAM.
Later, writeback to the actual swap device is deferred or even completely avoided, resulting in a significantly reduced I/O for Linux systems that require swapping
(source: wikipedia )
Maybe a stupid question by me, but I´d like to ask it anyway. 
As zram
provides a compressed block device using RAM for storing data, which acts as a regular and separate swap device.
… would it theoretically be possible to use zram and zswap together (at the same time) 
I´m sure with my 4 GB RAM that wouldn´t much sense. Therefore my theoretical question.
Many greetings
Rosika 