Re: [PATCH v1 2/2] read-cache: make sure file handles are not inherited by child processes

From: Junio C Hamano <gitster@pobox.com>
Date: Sep 7, 2016, 18:23 UTC
Message-ID: <xmqqtwdrmuvo.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <20160907181036.GA14931@starla>

Eric Wong <e@80x24.org> writes:

> We probably should be using O_NOATIME for all O_RDONLY cases
> to get the last bit of performance out (especially since
> non-modern-Linux systems probably still lack relatime).

No, please do not go there.

The user can read from a file in a working tree using "less", "grep", etc., and they all update the atime, so should "git grep". We do not use atime ourselves on these files but we should let outside tools rely on the validity of atime (e.g. "what are the files that were looked at yesterday?").

If you grep for noatime in our current codebase, you'd notice that we use it only for files in objects/ hierarchy, and that makes very good sense. These files are what we create for our _sole_ use and no other tools can peek at them and expect to get any useful information out of them (we hear from time to time that virus scanners leaving open file descriptors on them causing trouble, but that is an example of a useless access), and that makes a file in objects/ hierarchy a fair game for noatime optimization.