"Zswap is a Linux kernel feature providing a compressed write-back cache for swapped pages. 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 inside system's RAM." - Wikipedia
In simple words, zswap - no swap as zram(compcache) or swap file/partition. Zswap only interlayer, for work this feature you need manually setup swap partition/file.
Get in work
For enable zswap, add to kernel boot options (line) this:
For customize maximum allowing size:
For specify compress algorithm: