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Replacing Atime With Relatime in the Kernel
eldavojohn writes "Our friend Jeremy at the Kernal Trap has dug up some interesting criticism of atime from Linus Torvalds. As Linus submitted patches to improve relatime he noted: 'I cannot over-emphasize how much of a deal it is in practice. Atime updates are by far the biggest IO performance deficiency that Linux has today. Getting rid of atime updates would give us more everyday Linux performance than all the pagecache speedups of the past 10 years, _combined_.' And later severely beat atime about the head with a pointed stick: 'It's also perhaps the most stupid Unix design idea of all times. Unix is really nice and well done, but think about this a bit: 'For every file that is read from the disk, lets do a ... write to the disk! And, for every file that is already cached and which we read from the cache ... do a write to the disk!'" Well, I guess I can expect my Linux machine to become a little bit faster!"
After I mounted my system with nodiratime and noatime, I did not 'feel' any actual speed increase. I didn't did any hard testing of course.
Disclaimer: Disregard the above post.
Seriously. Many have recommended mounting filesystems with the "noatime" parameter if you don't need to know atime for many years now,
if the poster had read the article they would have noticed that Linus did not say those things that are quoted - Ingo Molnar did.
Amazingly, standard Unix filesystems keep time of last access (atime), change of status (ctime), and file modification (mtime) but do not remember when the file was first created, which is something I have frequently wished for.
Intron: the portion of DNA which expresses nothing useful.
/media/sda1 ext3 defaults,noatime 1 1 atime logs when a file has been written or read. So every time a file is used, it has to write an entry on the HDD, slowing performance, but it can have uses, like in forensics, security or backups (if a file has not been read in three years, it's probably safe to archive and move off the drive). I don't care for it, so I have the noatime line in my fstab.There is no "I disagree" mod for a reason. Flamebait, Troll, and Overrated are not substitutes.
File access timestamps, by default, are updated each time a file is read, and this occurs a write to the disk. Even if a file resides in cache, a write must be performed every time it is opened [even though the cache prevents a read from the disk]. A few people found that by disabling this, performance increases dramatically. The long and short of it: use noatime when you're mounting a file system [or in the fstab] if you want to try for yourself.
becomes
Deferred, maybe, but not for more than a few seconds, and when it happens it means more disk seeks...
It's long been standard practice to disable this on, eg, news/mail spools (anything with large numbers of read-mostly small files). The new plan of, if I understand correctly, only updating atime when the file is modified or if the new atime is more than 24 hours after the current atime should provide nearly the same functionality with practically none of the performance hit.
"You fell victim to one of the classic blunders! The most famous is never get involved in a flame war on Kerneltrap..."
"Can of worms? The can is open... the worms are everywhere."
Hey, Slashdot posted an article about me! [ They also renamed me to Linus - what more can a geek ask for? ;-) ]
In any case, the latest version of the better-relatime patch can be picked up from:
http://redhat.com/~mingo/relatime-patches/
Apply it, build it, reboot into the new kernel and enjoy a faster (and lower latency) desktop. (no fstab twiddling needed)
Just a handy tip for you (if you don't already use it) or others who are looking at disabling atime more for the power savings than the IO -- on laptops you should also be using noflushd (non-journaling filesystems only) or (ideally) Laptop Mode Tools. Also do not forget to configure syslog so that it doesn't constantly sync writes.
It's also worth mentioning that you *can* have atime enabled with properly configured laptop-mode and laptop-mode-tools and still see almost as much power savings -- The atime writes will still happen, but at least they will be buffered for when the HDD actually needs to spin up and do a lot of other more pressing IO.
However Mutt's use of atime simply is cheap enough that there's simply never been a reason to change it all the time most people have had atime updates on anyway. If it ain't broke, don't fix it.
On of my gripes with Linux is that one cannot spin down the disks to lessen their wear and tear.
Ive been told that the kernel constantly needs to access the disk...
Is this the reason of something else prevents the disks from spinning down?
If you're using a desktop system with a hard disk you'll hardly notice any difference unless you hammer the system really hard.
Remember though that most Linux systems are either embedded (using mainly flash) or servers. In both these cases atime updates can be very damaging to performance and should be avoided unless there's a very good reason to turn it on.
Engineering is the art of compromise.
(mount ext3 filesystem with noatime flag)
$ time for i in `seq 1 10000`; do touch file1.dat; done
real 0m15.231s
user 0m3.075s
sys 0m11.970s
$ time for i in `seq 1 10000`; do cat file1.dat >>/dev/null; done
real 0m14.326s
user 0m2.928s
sys 0m11.172s
(remount without noatime flag)
$ time for i in `seq 1 10000`; do touch file1.dat; done
real 0m12.629s
user 0m2.687s
sys 0m9.772s
$ time for i in `seq 1 10000`; do cat file1.dat >>/dev/null; done
real 0m12.401s
user 0m2.624s
sys 0m9.624s
Yes I think I'll stick with atime for now, thanks Linus.
"Nine times out of ten, starting a fire is not the best way to solve the problem." - my wife
Of course, I have to question why they're still using something as ancient as MUTT.
The thing I really *really* like about Mutt is that it uses Unix mailbox files. These are not just human-readable, they can also be manipulated using tools like 'cat'. I periodically archive my working mail files into a backup directory by just concatenating the working files onto the archive files of the same name. The resulting archive mail files are still fully usable with Mutt, even though some are 100Mb+ in size with mail going back to 1997. I could also use them with even older mail clients such as Pine, but that would be like using vi when you've got vim.
When I initially began using Linux, I used the Netscape email software, got fed up with it, and tried a few other mail clients. But none of them came close to the flexibility of Mutt. They all used their own mailbox formats, which could not be archived in the way I just described. I suspect that this is still true. I'm not going to trust Opera, Sylpheed, Thunderbird or Evolution with my mail, because (a) I doubt present-day mail files will still work reliably in 10 years time, (b) I can't easily migrate to another mail reader, and (c) I can't efficiently archive my email because the database files are not plain text.
That's why I like Mutt, anyway.
>north
You're an immobile computer, remember?
How can anyone write that with a straight face?
Every time I start to have faith in humanity, I ruin it by driving to work between 7 and 8 am.
But sometimes you need it... Whether it is to project your savings or to figure out, if a particular file was read within the last year.
My problem with atime is that it is not universal enough. For example, reading a file via mmap() or sending it directly to a socket via sendfile() (both methods widely used by web-servers) will not update its atime. The access-timestamp should be updated every time a file is opened for reading, rather than when a read() is issued on it...
So, when I wanted to report, when my little piece of software was last downloaded (via HTTP), I could not, unfortunately, rely on the file's atime...
In Soviet Washington the swamp drains you.
I'm not sure your link is correct.
I don't think you can fully realize how poetic a phrase such as the one above can be until you read it with absolutely no understanding, as I do.
Thank you, ArcherB and thank you, Slashdot.
You are welcome on my lawn.
I'm sure it was written with a gay face.
"THERE IS NO JUSTICE, THERE IS ONLY ME." -Death