linux-kernel - Re: [PATCH v8 0/5] fs: multigrain timestamps for XFS's change

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Message-ID: <9b81a1f52b4dc777dbb5259b2e12e90eba0ff507.camel@kernel.org>
Date:   Mon, 25 Sep 2023 06:17:14 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     NeilBrown <neilb@...e.de>, Christian Brauner <brauner@...nel.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Chuck Lever <chuck.lever@...cle.com>,
        Olga Kornievskaia <kolga@...app.com>,
        Dai Ngo <Dai.Ngo@...cle.com>, Tom Talpey <tom@...pey.com>,
        Chandan Babu R <chandan.babu@...cle.com>,
        "Darrick J. Wong" <djwong@...nel.org>,
        Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.cz>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Kent Overstreet <kent.overstreet@...ux.dev>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-xfs@...r.kernel.org
Subject: Re: [PATCH v8 0/5] fs: multigrain timestamps for XFS's change_cookie

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@...nel.org>