Linux: Replacing atime With relatime

“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 atime…”

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