In a recent lkml thread, Linus Torvalds was involved in a discussion about mounting filesystems with the
noatime option for better performance, "'noatime,data=writeback' will quite likely be *quite* noticeable (with different effects for different loads), but almost nobody actually runs that way." He noted that he set O_NOATIME when writing git, "and it was an absolutely huge time-saver for the case of not having 'noatime' in the mount options. Certainly more than your estimated 10% under some loads." The discussion then looked at using the
relatime mount option to improve the situation, "relative atime only updates the atime if the previous atime is older than the mtime or ctime. Like noatime, but useful for applications like mutt that need to know when a file has been read since it was last modified." Ingo Molnar stressed the significance of fixing this performance issue, "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_." He submitted some patches to improve
relatime, and noted about
"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!'"
The Linux Kernel Archives are perhaps most familiar through their web interface, http://kernel.org/. The latest release of the Linux kernel is easily found here, along with patches by various Linux kernel hackers, and mirrors of other popular free and open source projects. Countless people worldwide happily rely on this archive without giving much thought to the effort behind it.
In a recent announcement to the Linux Kernel Mailing List, H. Peter Anvin detailed a recent upgrade of the infrastructure behind kernel.org. The new servers were donated by Hewlett-Packard, and are each quad Opterons with 24 gigabytes of RAM and 10 terabytes of disk space. Internet Systems Consortium, Inc. donates the bandwidth in the form of two independent gigabit-connected datacenters, PAIX Palo Alto and e200paul in San Francisco. H. Peter Anvin, Nathan Laredo, and Kees Cook all donate time to maintain the archives. KernelTrap recently spoke with Peter Anvin to learn more about the history behind the Linux Kernel Archives.