linux-kernel - Re: [PATCH 00/10] HMM updates for 5.1

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Message-ID: <20190319222445.GD3096@redhat.com>
Date:   Tue, 19 Mar 2019 18:24:45 -0400
From:   Jerome Glisse <jglisse@...hat.com>
To:     Ira Weiny <ira.weiny@...el.com>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Christian König <christian.koenig@....com>,
        Ralph Campbell <rcampbell@...dia.com>,
        John Hubbard <jhubbard@...dia.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Alex Deucher <alexander.deucher@....com>
Subject: Re: [PATCH 00/10] HMM updates for 5.1

On Tue, Mar 19, 2019 at 07:18:26AM -0700, Ira Weiny wrote:
> On Tue, Mar 19, 2019 at 12:13:40PM -0700, Dan Williams wrote:
> > On Tue, Mar 19, 2019 at 12:05 PM Jerome Glisse <jglisse@...hat.com> wrote:
> > >
> > > On Tue, Mar 19, 2019 at 11:42:00AM -0700, Dan Williams wrote:
> > > > On Tue, Mar 19, 2019 at 10:45 AM Jerome Glisse <jglisse@...hat.com> wrote:
> > > > >
> > > > > On Tue, Mar 19, 2019 at 10:33:57AM -0700, Dan Williams wrote:
> > > > > > On Tue, Mar 19, 2019 at 10:19 AM Jerome Glisse <jglisse@...hat.com> wrote:
> > > > > > >
> > > > > > > On Tue, Mar 19, 2019 at 10:12:49AM -0700, Andrew Morton wrote:
> > > > > > > > On Tue, 19 Mar 2019 12:58:02 -0400 Jerome Glisse <jglisse@...hat.com> wrote:
> 
> [snip]
> 
> > >
> > > Right now i am trying to unify driver for device that have can support
> > > the mmu notifier approach through HMM. Unify to a superset of driver
> > > that can not abide by mmu notifier is on my todo list like i said but
> > > it comes after. I do not want to make the big jump in just one go. So
> > > i doing thing under HMM and thus in HMM namespace, but once i tackle
> > > the larger set i will move to generic namespace what make sense.
> > >
> > > This exact approach did happen several time already in the kernel. In
> > > the GPU sub-system we did it several time. First do something for couple
> > > devices that are very similar then grow to a bigger set of devices and
> > > generalise along the way.
> > >
> > > So i do not see what is the problem of me repeating that same pattern
> > > here again. Do something for a smaller set before tackling it on for
> > > a bigger set.
> > 
> > All of that is fine, but when I asked about the ultimate trajectory
> > that replaces hmm_range_dma_map() with an updated / HMM-aware GUP
> > implementation, the response was that hmm_range_dma_map() is here to
> > stay. The issue is not with forking off a small side effort, it's the
> > plan to absorb that capability into a common implementation across
> > non-HMM drivers where possible.
> 
> Just to get on the record in this thread.
> 
> +1
> 
> I think having an interface which handles the MMU notifier stuff for drivers is
> awesome but we need to agree that the trajectory is to help more drivers if
> possible.
> 

Yes and i want to get there step by step not just in one giant leap.
It seems Dan would like to see this all one step and i believe this
is too risky and make the patchset much bigger and harder to review.

Cheers,
Jérôme