The zswap compressed swap cache

Both zcache and zswap do compressed swap page caching. However, zcache uses the tmem API internally that creates an abstraction layer for doing a number of other things like compressed file page caching via cleancache and, more recently, remote RAM (RAMster).

So same problem, different solution. zswap focuses solely on compressed swap caching which removes the need for an abstraction layer, resulting in a smaller code base.

Both can be built in the same kernel, but you would only enable one at a time. Both zswap and zcache are enabled through a boot parameters for now.

Neither is in mainline yet and discussions are (or will be) ongoing on LKML about what to do going forward. There has been a LSF/MM topic suggested for this very discussion (http://marc.info/?l=linux-mm&m=135923138220901)