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

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Date:   Tue, 26 Sep 2023 14:18:39 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     NeilBrown <neilb@...e.de>
Cc:     Jeff Layton <jlayton@...nel.org>,
        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

> > 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

> 
> Some NFS servers run in userspace, and they would a "clear user" of this
> functionality.

See my comment above. We did thist mostly for the sake of NFS as there
was in itself nothing wrong with timestamps that needed urgent fixing.

The end result has been that we caused a regression for four other major
filesystems when they were switched to fine-grained timestamps.

So NFS servers in userspace isn't a sufficient argument to just try
again with a slightly tweaked solution but without a wholesale fix of
the actual ordering problem. The bar to merge this will naturally be
higher the second time around.

That's orthogonal to improving the general timestamp infrastructure in
struct inode ofc.