Project Description

zswap [1] is a linux kernel component that provides in-memory compression for swap pages. It already provides a limited form of deduplication: if a page is filled with the same value (e.g. all-zeroes) then only that value is kept instead of compressing the contents.

This project proposes to enhance zswap with a more general and powerful dedup capability: pages that contain the same content (as identified by a checksum or hash value across the entire page contents) will be stored only once in the compressed pool.

This would be somewhat similar in spirit to what ksm [2] does, that is consolidation of identical pages of anonymous memory. There are some differences though, primarily ksm requires userspace to explicitly opt-in (via madvise/MADV_MERGEABLE) and operates on active pages that have not been selected for eviction from memory. On the other hand zswap operates transparently from the applications (it applies to all pages of anonymous memory that are on their way to swap).

Goal for this Hackweek

Have a first working POC.

Resources

• [1] https://www.kernel.org/doc/html/latest/admin-guide/mm/zswap.html
• [2] https://www.kernel.org/doc/html/latest/admin-guide/mm/ksm.html