This new patch, which could be merged into the Linux 3.3 kernel, lets zcache use the generic Crypto compression API and from there any compressor can be selected for zcache via a kernel module parameter. Zcache allows for dynamic compression of swap pages and clean pagecache pages. Zcache is one of the users of the recently-merged Linux kernel CleanCache. Zcache is currently living in the Linux kernel staging area after its 2010 introduction.
For those not familiar with Zcache, the kernel configuration describes it as "[doubling] RAM efficiency while providing significant performance boosts on many workloads. Zcache uses compression and an in-kernel implementation of transcendent memory to storage clean page cache pages and swap in RAM, providing a noticeable reduction in disk I/O."
For those not opting for a different Crypto compressor, LZO remain the default means of page compression.
More details in this kernel mailing list announcement.