[adamtj]

> touch all source code files (this step is mandatory, or else the atime won't update correctly, I don't know why, but guess it's an optimization).

On a filesystem mounted with the "relatime" option, it's necessary to touch each file so that the next access is guaranteed to bump the atime.

It used to be common to update the access time every time a file was accessed. That turned every read into a read+write, which is expensive. Linux filesystems are now commonly mounted with either the "relatime" or "noatime" options. "noatime" does what you'd expect. "relatime" is a compromise. It updates the atime on access only if it's the same as the mtime -- in other words, only once after a write. I think some mail or news readers consider a message to be read only if atime > mtime. They won't work right with "noatime".

http://serverfault.com/questions/47466/drawbacks-of-mounting...

[baohaojun]

Thanks for the info, it must be the relatime that I saw this behavior. Were it noatime, this idea won't have worked at all (I think I have seen noatime used on embedded devices).