the log writing should be fadvised as "don't cache for long" as we typically don't go back and read it. if the log were gigantic, this will push db data out of the filesystem cache if the data is touched infrequently.

the same would apply to other files that output big files we don't need – not sure what those are – mongodump? mongoexport? i guess most temp files we generate we quickly use so probably doesn't make sense there.