The zswap compressed swap cache

Posted Feb 15, 2013 10:58 UTC (Fri) by geuder (subscriber, #62854)
Parent article: The zswap compressed swap cache

So how does zswap relate to zcache? (https://lwn.net/Articles/537760/ , http://lwn.net/Articles/397574/) Different problem or different solution? Mutually exclusive or could be combined inside the same kernel? Found also http://lwn.net/Articles/528817/, but still a bit confused...

The zswap compressed swap cache

Posted Feb 15, 2013 16:58 UTC (Fri) by sjennings (guest, #74813) [Link]

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)

The zswap compressed swap cache

Posted Feb 18, 2013 17:21 UTC (Mon) by djm1021 (guest, #31130) [Link]

As Seth responded, zcache is part of a larger portfolio of inter-related code and objectives, called Transcendent Memory (or "tmem"), supporting different kinds of "input" data (frontends) and different "data stores" (backends). Tmem and its friends are described here: http://lwn.net/Articles/454795/
Avi Miller gave a talk on it at linux.conf.au last month and the recording of that talk can be found here: http://mirror.linux.org.au/linux.conf.au/2013/ogv/Transce...