Wow, I'd love to know what they mean by "imperfect". In Linux, specifically, the sync_dirty_buffers syncs all the dirty write buffers (nope - see edit) and isn't imperfect or incomplete in any particular way.
Edit: Nevermind, I'm remebering now there is a dirty_background_ratio separate from a dirty_ratio. It will sync some of the dirty buffers as long as it's above dirty_background_ratio and under dirty_ratio. And it was actually bdflush that determined all of this; the sync_dirty_buffer function just took a specific buffer object and synced that.
Edit 2: And I'm finding out that information seems to be outdated. Here's the old documentation about bdflush [1].
That was either moved or removed in the latest version, but I did find this [2], which suggests that there was an old bdflush vs something else now. Looks like I missed something important and have some research to do.
[1] http://lxr.free-electrons.com/source/Documentation/sysctl/vm...
[2] http://lxr.free-electrons.com/source/Documentation/vm/active...