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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.
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
"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.
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.
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.
I'm sure it was written with a gay face.
"THERE IS NO JUSTICE, THERE IS ONLY ME." -Death