Re: [PATCH v8 0/5] fs: multigrain timestamps for XFS's change_cookie

[Jeff Layton]

On Mon, 2023-09-25 at 08:44 +1000, NeilBrown wrote:
> On Sun, 24 Sep 2023, Christian Brauner wrote:
> > > My initial goal was to implement multigrain timestamps on most major
> > > filesystems, so we could present them to userland, and use them for
> > > NFSv3, etc.
> > 
> > If there's no clear users and workloads depending on this other than for
> > the sake of NFS then we shouldn't expose this to userspace. We've tried
> > this and I'm not convinced we're getting anything other than regressions
> > out of it. Keep it internal and confined to the filesystem that actually
> > needs this.
> > 
> 
> Some NFS servers run in userspace, and they would a "clear user" of this
> functionality.
> 

Indeed. Also, all of the programs that we're concerned about breaking
here (make, rsync, etc.) could benefit from proper fine-grained
timestamps:

Today, when they see two identical timestamps on files, these programs
have to assume the worst: rsync has to do the copy, make has to update
the target, etc. With a real distinguishable fine-grained timestamps,
these programs would likely be more efficient and some of these unneeded
operations would be avoided.
-- 
Jeff Layton <jlayton@xxxxxxxxxx>