Messages in this thread |  | | Date | 10 Sep 2001 10:30:00 +0200 | From | (Kai Henningsen) | Subject | Re: linux-2.4.10-pre5 |
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sim@netnation.com (Simon Kirby) wrote on 09.09.01 in <20010909173947.A20202@netnation.com>:
> What do people actually use atime for, anyway? I've always > noatime/nodiratime'd most servers I've set up because it saves so much > disk I/O, and I have yet to see anything really use it. I can see that > in some cases it would be useful to turn it _on_ (perhaps for debugging / > removal of unused files, etc.), but it seems silly that the default case > is a situation which on the surface seems dumb (opening a file for read > causes a disk write).
I see two possible atime uses:
1. Cleaning up /tmp (mtime is *not* a good indicator that a file is no longer used) 2. Swapping out files to slower storage
Essentially, both use the "do we still need this thing" aspect.
Of course, for this to be useful, we really need programs to be able to say "ignore my use of this file". tar --atime-preserve, for example (which, incidentally, notes a technical problem with doing this). I'd also add stuff like files or md5sum or similar diagnostic tools to the "might want to not affect atime" list, and possibly also stuff like inn ("atime on /var/spool/news is just silly").
HOWEVER, I'd think what would really be nice for this would be an O_NOATIME flag (which does enforce read-only operation, of course), and not fixing the atime back afterwards (inherently racy, but even more so by design of utimes and ctime).
That flag would also be fairly easy to detect with autoconf or similar functionality.
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