As others have pointed out, the point of zswap is to "swap" in and out of RAM. I'd like to add that your premise is faulty anyway: since compressed objects are

As others have pointed out, the point of zswap is to "swap" in and out of RAM. I'd like to add that your premise is faulty anyway: since compressed objects are smaller doing I/O on them is faster. As long as cost of the I/O you saved is less than the cost of doing the compression, it's faster not slower. Transparently compressed I/O usually uses high-speed algorithms (LZ4, LZO, etc) to take advantage of this effect. Also, when a machine is swapping you'll usually find that the CPU is near idle since useful work is blocked on the swap I/O. Spending a little CPU time to speed up that I/O is a win.