linux-kernel - Re: [Cluster-devel] [PATCH 06/32] sched: Add task_struct->faults_disabled

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Date:   Wed, 24 May 2023 04:09:02 -0400
From:   Kent Overstreet <kent.overstreet@...ux.dev>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Jan Kara <jack@...e.cz>, cluster-devel@...hat.com,
        "Darrick J . Wong" <djwong@...nel.org>,
        linux-kernel@...r.kernel.org, dhowells@...hat.com,
        linux-bcachefs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Kent Overstreet <kent.overstreet@...il.com>
Subject: Re: [Cluster-devel] [PATCH 06/32] sched: Add
 task_struct->faults_disabled_mapping

On Tue, May 23, 2023 at 11:43:32PM -0700, Christoph Hellwig wrote:
> On Tue, May 23, 2023 at 12:35:35PM -0400, Kent Overstreet wrote:
> > No, this is fundamentally because userspace controls the ordering of
> > locking because the buffer passed to dio can point into any address
> > space. You can't solve this by changing the locking heirarchy.
> > 
> > If you want to be able to have locking around adding things to the
> > pagecache so that things that bypass the pagecache can prevent
> > inconsistencies (and we do, the big one is fcollapse), and if you want
> > dio to be able to use that same locking (because otherwise dio will also
> > cause page cache inconsistency), this is the way to do it.
> 
> Well, it seems like you are talking about something else than the
> existing cases in gfs2 and btrfs, that is you want full consistency
> between direct I/O and buffered I/O.  That's something nothing in the
> kernel has ever provided, so I'd be curious why you think you need it
> and want different semantics from everyone else?

Because I like code that is correct.