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Subject: Re: [PATCH v8 0/5] fs: multigrain timestamps for XFS's change_cookie
From:   Jeff Layton <jlayton@kernel.org>
To:     NeilBrown <neilb@suse.de>, Christian Brauner <brauner@kernel.org>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Chuck Lever <chuck.lever@oracle.com>,
        Olga Kornievskaia <kolga@netapp.com>,
        Dai Ngo <Dai.Ngo@oracle.com>, Tom Talpey <tom@talpey.com>,
        Chandan Babu R <chandan.babu@oracle.com>,
        "Darrick J. Wong" <djwong@kernel.org>,
        Dave Chinner <david@fromorbit.com>, Jan Kara <jack@suse.cz>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Kent Overstreet <kent.overstreet@linux.dev>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-nfs@vger.kernel.org, linux-xfs@vger.kernel.org
Date:   Mon, 25 Sep 2023 06:17:14 -0400
In-Reply-To: <169559548777.19404.13247796879745924682@noble.neil.brown.name>
References: <20230922-ctime-v8-0-45f0c236ede1@kernel.org>
        , <20230924-mitfeiern-vorladung-13092c2af585@brauner>
         <169559548777.19404.13247796879745924682@noble.neil.brown.name>
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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.
> >=20
> > If there's no clear users and workloads depending on this other than fo=
r
> > 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 regression=
s
> > out of it. Keep it internal and confined to the filesystem that actuall=
y
> > needs this.
> >=20
>=20
> Some NFS servers run in userspace, and they would a "clear user" of this
> functionality.
>=20

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.
--=20
Jeff Layton <jlayton@kernel.org>