Zswap
Zswap is 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. Older pages can be evicted to disk making this a sort of write-behind cache. zswap basically trades CPU cycles for potentially reduced swap I/O.
Benefits of usage
- Systems with limited RAM capacities can have the performance impact of swapping mitigated.
- Systems with SSDs as swap devices can extend the life of the device by drastically reducing life-shortening writes.
How to enable/disable Zswap
Zswap is disabled by default but can be enabled at boot time by setting the enabled attribute to 1 at boot time. ie: zswap.enabled=1. Zswap can also be enabled and disabled at runtime using the sysfs interface. An example command to enable zswap at runtime, assuming sysfs is mounted at /sys, is:
echo 1 > /sys/module/zswap/parameters/enabled
Alternative
Similar results as with Zswap can be achieved with Zram. Zram though eliminates the need for physical swap device.
Here's an excellent article that explains how ZRAM and ZSWAP work and what the differences are. It can be very helpful in determining which one is best to use and how.