bug#18406: O_NOATIME patch

[Jim Meyering]

On Tue, Sep 1, 2020 at 4:22 AM Paul Eggert <eggert@cs.ucla.edu> wrote:
> On 9/11/14 1:13 PM, Paul Eggert wrote:
> > Thanks, but there's no need for that; just have 'grep' complain if the 
> > option is
> > used and O_NOATIME == 0.
>
> On looking into this more today, O_NOATIME seems to be just a best-effort 
> thing
> as some GNU/Linux filesystems ignore it, so grep should just join the throng 
> and
> not worry whether O_NOATIME actually works.
>
> Also, the O_NOATIME support was withdrawn from fts a couple of years ago, so
> 'grep -r' can't easily avoid updating atime on directories.
>
> A patch is attached. I'm still of two minds about this. The efficiency 
> argument
> for the new option is not as strong as it used to be, now that relatime has
> taken over on ext4 style filesystems. So the main argument is "I want to 
> search
> through this directory but don't want it to count as an access"; although 
> that's
> indeed a use case I'm not quite sure it's worth modifying 'grep' over. It
> doesn't seem to be worth using up a scarce option letter over, anyway, so the
> attached patch uses just a long option.

I confess to similar ambivalence, but do like the idea. Has anyone run
tests to compare performance on file systems like ext4, btrfs (the
default with Fedora 33) and xfs?