linux-kernel - Re: [PATCH 09/10] mm/hmm: allow to mirror vma of a file on a DAX backed filesystem

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Date:   Wed, 6 Mar 2019 14:18:20 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Jerome Glisse <jglisse@...hat.com>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ralph Campbell <rcampbell@...dia.com>,
        John Hubbard <jhubbard@...dia.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 09/10] mm/hmm: allow to mirror vma of a file on a DAX
 backed filesystem

On Wed, 6 Mar 2019 10:49:04 -0500 Jerome Glisse <jglisse@...hat.com> wrote:

> On Tue, Mar 05, 2019 at 02:16:35PM -0800, Andrew Morton wrote:
> > On Wed, 30 Jan 2019 21:44:46 -0800 Dan Williams <dan.j.williams@...el.com> wrote:
> > 
> > > >
> > > > > Another way to help allay these worries is commit to no new exports
> > > > > without in-tree users. In general, that should go without saying for
> > > > > any core changes for new or future hardware.
> > > >
> > > > I always intend to have an upstream user the issue is that the device
> > > > driver tree and the mm tree move a different pace and there is always
> > > > a chicken and egg problem. I do not think Andrew wants to have to
> > > > merge driver patches through its tree, nor Linus want to have to merge
> > > > drivers and mm trees in specific order. So it is easier to introduce
> > > > mm change in one release and driver change in the next. This is what
> > > > i am doing with ODP. Adding things necessary in 5.1 and working with
> > > > Mellanox to have the ODP HMM patch fully tested and ready to go in
> > > > 5.2 (the patch is available today and Mellanox have begin testing it
> > > > AFAIK). So this is the guideline i will be following. Post mm bits
> > > > with driver patches, push to merge mm bits one release and have the
> > > > driver bits in the next. I do hope this sound fine to everyone.
> > > 
> > > The track record to date has not been "merge HMM patch in one release
> > > and merge the driver updates the next". If that is the plan going
> > > forward that's great, and I do appreciate that this set came with
> > > driver changes, and maintain hope the existing exports don't go
> > > user-less for too much longer.
> > 
> > Decision time.  Jerome, how are things looking for getting these driver
> > changes merged in the next cycle?
> 
> nouveau is merge already.

Confused.  Nouveau in mainline is dependent upon "mm/hmm: allow to
mirror vma of a file on a DAX backed filesystem"?  That can't be the
case?

> > 
> > Dan, what's your overall take on this series for a 5.1-rc1 merge?
> > 
> > Jerome, what would be the risks in skipping just this [09/10] patch?
> 
> As nouveau is a new user it does not regress anything but for RDMA
> mlx5 (which i expect to merge new window) it would regress that
> driver.

Also confused.  How can omitting "mm/hmm: allow to mirror vma of a file
on a DAX backed filesystem" from 5.1-rc1 cause an mlx5 regression?