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(Get the code!)
Ted,
I am not sure if this was covered yet but if so I apologize in advance for beating a dead horse.
The current opinion is that if you want to make meta data (eg the out of order rename case) reliable you must use sync... Ok, that would require a huge number of changes to many programs but it is at least theoretically doable. However in doing so aren't you rendering laptop mode essentially useless? As far as I know and from mjg59 confirmed was the case you can't delay syncs. So now any time in the future any application that wants its data to be reliable if only for meta data cases it will cause a drive to spin up causing battery life to go down the tubes. Yes SSDs are much more power efficient and are the wave of the future, but from where I am it looks like they will continue to be the wave of the future, what with even the Intel SSDs being only rated for 20GB/day data transfer.
Also, you mentioned before that attempting to track meta data ordering for files in memory would cause entaglement forcing a write of all data to disk. Is that just due to the way the current kernel filesystem layer works or a problem that is not fixable? If it were fixable then sync's in code would only be needed for critical writes since meta data being out of order would no longer cause the serious problems it does today in cases with no sync calls. This would allow much more efficient power management of hard drives since a laptop could potentially go for a very long time without needing to spin up the hard drive (or bring the SSD out of low power mode).
You also did mention that in the case of saving to a remote filesystem that sync is actually needed to determine if it is even possible to save to it. With the way the desktop in the past had worked, mounting remote filesystems using the kernel and using posix apis, it was unknown what the user would be saving to so apps might just sync to be safe. However I think this case may not be as big of an issue anymore, on the desktop at least, due to moving to api's such as gio which already know if they are saving to a remote filesystem so can sync only in those cases, at least aiui.