Messages in this thread | | | Date | Fri, 10 Aug 2007 15:29:27 -0400 | From | Bill Davidsen <> | Subject | Re: Noatime vs relatime |
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Vlad wrote: > Linus Torvalds wrote: >> What we could do is to make "relatime" updates a bit smarter. >> >> A bit smarter would be: >> >> - update atime if the old atime is <= than mtime/ctime >> >> Logic: things like mailers can care about whether some >> new state has >> been read or not. This is the current relatime. >> >> - update atime if the old atime is more than X seconds >> in the past (defaulting to one day or something) >> >> Logic: things like tmpwatch and backup >> software may want to remove >> stuff that hasn't been touched in a long time, but they >> sure don't care about "exact" atime. > > Relatime seems to be wasteful of both IO resources _and_ CPU cycles. > Instead of performing a single IO operation (as atime does), relatime > performs at least three IO operations and three CPU-dependent > operations: > > 1) a read IO operation to find out the old atime > 2) a read IO operation to find out the old ctime > 3) a read IO operation to find out the old mtime
Reading a value in memory into a CPU register is not normally considered an I/O operation.
> 4) Comparison of "old atime is <= than mtime/ctime" > 5) Find out current time > 6) Comparison of "current time minus old atime is > X" > > People are going to wonder why all of the sudden everything is running > so slow due to atimes being updated after a long break. > > I suggest treating atime as if it were a subsystem that is scheduled > for an overhaul - there have been plenty of those in the past. Give > users/distros a config option to disable atime, but default this > option in favor of atime for a couple of kernel release cycles. Print > a line in dmesg that states something like: > > "Warning: Atime will be disabled by default in future kernel versions, > but you will still be able to turn it on when configuring the kernel." > > This should give a heads-up to the 0.001% of people who still use > atime so that they know to customize this option or start using modern > file-monitoring techniques like inotify. > > Vlad > > > > ____________________________________________________________________________________ > Pinpoint customers who are looking for what you sell. > http://searchmarketing.yahoo.com/
-- Bill Davidsen <davidsen@tmr.com> "We have more to fear from the bungling of the incompetent than from the machinations of the wicked." - from Slashdot - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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