> Only right now, the cache application causes files to disappear at random points in time. Volatile ranges on files just moves a common cache management mechanism into the filesystem so it can be done when the filesystem needs it to be done....
Yes, and having filesystems able to disappear (parts of) files all by themselves with no application involvement seems like a *major* change, and seems rather scary to me.
I mean, in the intended usage, the application itself expects its data to disappear, sure. But, I'm wondering about other knock-on effects of these sorts of files being able to exist. Will I, as admin, be able to easily tell that some files are "disappear-y"? New feature added to "ls"? How can I tell how much space is used by such data? New fields in "df"?
What sorts of controls over who can mark data like that will there be? Can it cause a security issue for data to disappear in the middle of a file unexpectedly? Maybe clearing volatile-ness on file ownership or permissions change fixes that?
I dunno...it just seems like so much complication versus in-memory volatility that it doesn't seem worth it. And, worse, pinning it to fallocate instead of something like madvise makes the API so much more fiddly to use for a simple in-memory case.