Bulma (the lug at Balearic Islands) has written an article called "Journal File Systems in Linux" "This is a lightly modified version of a couple of articles published in NovÃ¡tica (Spanish) and Upgrade (English) where we explain the implementation of all journaling file systems available for Linux."
Ricardo Galli includes, in a plain manner, its basics, characteristics and implementation (The Linux Virtual File
System, Linux Page-cache and Buffer-cache, Integration of page and buffer cache, Journaling File Systems, B-Trees,
ReiserFS, XFS, JFS, Ext3, Performance and Conclusions), including several links to Resources and Benchmarks.
Spanish version of the document also available."