Swapping out compressed data?

Your description gives me the impression that when the data needs to be swapped to the actual storage, it is done uncompressed (more precisely it's uncompressed and then written to backing store). That seems obviously suboptimal. Is it indeed the case, or can the compressed data be swapped out compressed?

Regarding the measurements: doing the measurement on machine with a crippled memory but a fast CPU seems unfair. A machine with 512MB of RAM is unlikely to have such a fast CPU, and a slower CPU makes compression less attractive since compression then takes more time. IOW measurements on a real 512MB machine (with something like a 1GHz Pentium, or an Allwinner A10) would seem more realistic.