One of the engineers at Google took the time to figure this out, and updated the page out code in the Linux kernel they were using so that the "correct" steps were known if you had to know your data was on disk. It was discussed on LKML as I recall but considered "not generally useful" and I doubt it made it into the main sources.

One of the interesting things about writes is that they disrupt reads more significantly than you might expect. Greg Lindahl characterized the impact at Blekko when we were crawling so that we could optimize writes from the crawl to not disrupt latency on the search engine side. Later we completely separated those functions for similar reasons. I believe every disk I've evaluated over the years is slowest on the random read/write 50% test.