Re: [Cluster-devel] [PATCH 06/32] sched: Add task_struct->faults_disabled_mapping

From: Kent Overstreet
Date: Wed May 24 2023 - 04:09:27 EST

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.