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From:   Dan Williams <dan.j.williams@intel.com>
Date:   Tue, 12 Mar 2019 18:06:23 -0700
Message-ID: <CAPcyv4htpVHm9GSYdKS=i4Ry011XZQUkOdMz9CXMrxJccRW9tw@mail.gmail.com>
Subject: Re: [PATCH 09/10] mm/hmm: allow to mirror vma of a file on a DAX
 backed filesystem
To:     Dave Chinner <david@fromorbit.com>
Cc:     Jerome Glisse <jglisse@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Ralph Campbell <rcampbell@nvidia.com>,
        John Hubbard <jhubbard@nvidia.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>
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On Tue, Mar 12, 2019 at 1:34 PM Dave Chinner <david@fromorbit.com> wrote:
>
> On Tue, Mar 12, 2019 at 12:30:52PM -0700, Dan Williams wrote:
> > On Tue, Mar 12, 2019 at 12:06 PM Jerome Glisse <jglisse@redhat.com> wrote:
> > > On Tue, Mar 12, 2019 at 09:06:12AM -0700, Dan Williams wrote:
> > > > On Tue, Mar 12, 2019 at 8:26 AM Jerome Glisse <jglisse@redhat.com> wrote:
> > [..]
> > > > > Spirit of the rule is better than blind application of rule.
> > > >
> > > > Again, I fail to see why HMM is suddenly unable to make forward
> > > > progress when the infrastructure that came before it was merged with
> > > > consumers in the same development cycle.
> > > >
> > > > A gate to upstream merge is about the only lever a reviewer has to
> > > > push for change, and these requests to uncouple the consumer only
> > > > serve to weaken that review tool in my mind.
> > >
> > > Well let just agree to disagree and leave it at that and stop
> > > wasting each other time
> >
> > I'm fine to continue this discussion if you are. Please be specific
> > about where we disagree and what aspect of the proposed rules about
> > merge staging are either acceptable, painful-but-doable, or
> > show-stoppers. Do you agree that HMM is doing something novel with
> > merge staging, am I off base there? I expect I can find folks that
> > would balk with even a one cycle deferment of consumers, but can we
> > start with that concession and see how it goes? I'm missing where I've
> > proposed something that is untenable for the future of HMM which is
> > addressing some real needs in gaps in the kernel's support for new
> > hardware.
>
> /me quietly wonders why the hmm infrastructure can't be staged in a
> maintainer tree development branch on a kernel.org and then
> all merged in one go when that branch has both infrastructure and
> drivers merged into it...
>
> i.e. everyone doing hmm driver work gets the infrastructure from the
> dev tree, not mainline. That's a pretty standard procedure for
> developing complex features, and it avoids all the issues being
> argued over right now...

True, but I wasn't considering that because the mm tree does not do
stable topic branches. This kind of staging seems not amenable to a
quilt workflow and it needs to keep pace with the rest of mm.