A lightweight compressed cache for swap pages. It takes
pages that are in the process of being swapped out and attempts to
compress them into a dynamically allocated RAM-based memory pool.
This can result in a significant I/O reduction on swap device and,
in the case where decompressing from RAM is faster that swap device
reads, can also improve workload performance.

This is marked experimental because it is a new feature (as of
v3.11) that interacts heavily with memory reclaim. While these
interactions don't cause any known issues on simple memory setups,
they have not be fully explored on the large set of potential
configurations and workloads that exist.

source code:

mm/zswap.c