slabtop command (part of the package procps) shows top memory objects used by the kernel.
dstat can help you figure out what is happening. dstat -cdnpmgs --top-bio --top-cpu --top-mem
Also have a look at smem ("smem -kt"), it can show you nicely what is in your swap.
ZRAM if you have no HDD/SSD swap partition.
ZSWAP if you do have a HDD/SSD swap partition.
ZCACHE: It does what ZSWAP does and ALSO compresses and speeds the filesystem page cache. (It is internally much more complicated and is not in the mainline kernel as it is still under development).
A CachedRowSet object is special in that it can operate without being connected to its data source, that is, it is a disconnected RowSet object. It gets its name from the fact that it stores (caches) its data in memory so that it can operate on its own data rather than on the data stored in a database.
M. Martin, J. Unbehauen, and S. Auer. Proceedings of 7th Extended Semantic Web Conference (ESWC 2010), 30 May -- 3 June 2010, Heraklion, Crete, Greece, volume 6089 of Lecture Notes in Computer Science, page 304-318. Berlin / Heidelberg, Springer, (2010)