Chris Down has posted a detailed look at how the kernel's zswap and zram subsystems work — and how they differ. Most people think of zswap and zram simply as two different flavours of the same thing: compressed swap. At a surface level, that's correct – both compress pages that would otherwise end up on disk – but they make fundamentally different bets about how the kernel should handle memory pressure, and picking the wrong one for your situation can actively make things worse than having no swap at all