Messages in this thread |  | | | Date | Fri, 5 Mar 1999 07:55:43 +1100 | | From | Richard Gooch <> | | Subject | Re: EXT2_UNRM_FL |
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Theodore Y. Ts'o writes: > Date: Thu, 4 Mar 1999 11:00:45 -0500 (EST) > From: "Albert D. Cahalan" <acahalan@cs.uml.edu> > There is another unrelated reason why the kernel must be involved. > You need to really delete files as the disk gets full. Polling is > just total crap, with race conditions and extra system load. You can > run out of disk space between two polls. That is not allowed. > > Polling simply means doing a quick statfs; that doesn't take much system > load. And obviously, you want to keep a fairly large amount of free > space to make sure the filesystem can do good block allocation --- for > example, you might use a high and low watermark of 5% and 10% of the > filesystem size. So unless you the user processes can consume that much > disk space between the two polls, you'll be fine. > > The grand Unix design transition is to try doing things in user space > first. If it doesn't work, then put in the minimal kernel hooks to > allow the Right Thing to happen. In this case, the smallest hooks would > be ones which can automatically wake up the daemon when filesystem space > starts getting critical.
Assuming you're not suggesting calling the daemon synchronously, then there still is a delay between when the FS starts getting full, and when the daemon can start purging. The delay between this and when free space becomes available may be a significant fraction of a second (especially if a lot of small files need to be deleted to make room for a big one). So polling once or twice a second might not have any significant impact, anyway.
> Also, please remember that there are plenty of user-space undelete > packages out there on the net; they apparently work just fine for > most people who have a desire for that kind of protection.
And I still wonder whether you really need to bury this in unlink(3) rather than rm(1).
Regards,
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