linux-kernel - Re: [PATCH v2 07/11] mm/hmm: add default fault flags to avoid the need to pre-fill pfns arrays.

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Message-ID: <20190329021225.GG16680@redhat.com>
Date:   Thu, 28 Mar 2019 22:12:25 -0400
From:   Jerome Glisse <jglisse@...hat.com>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Ben Skeggs <bskeggs@...hat.com>, Ira Weiny <ira.weiny@...el.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH v2 07/11] mm/hmm: add default fault flags to avoid the
 need to pre-fill pfns arrays.

On Thu, Mar 28, 2019 at 07:05:21PM -0700, John Hubbard wrote:
> On 3/28/19 6:59 PM, Jerome Glisse wrote:
> >>>>>> [...]
> >>>>> Indeed I did not realize there is an hmm "pfn" until I saw this function:
> >>>>>
> >>>>> /*
> >>>>>  * hmm_pfn_from_pfn() - create a valid HMM pfn value from pfn
> >>>>>  * @range: range use to encode HMM pfn value
> >>>>>  * @pfn: pfn value for which to create the HMM pfn
> >>>>>  * Returns: valid HMM pfn for the pfn
> >>>>>  */
> >>>>> static inline uint64_t hmm_pfn_from_pfn(const struct hmm_range *range,
> >>>>>                                         unsigned long pfn)
> >>>>>
> >>>>> So should this patch contain some sort of helper like this... maybe?
> >>>>>
> >>>>> I'm assuming the "hmm_pfn" being returned above is the device pfn being
> >>>>> discussed here?
> >>>>>
> >>>>> I'm also thinking calling it pfn is confusing.  I'm not advocating a new type
> >>>>> but calling the "device pfn's" "hmm_pfn" or "device_pfn" seems like it would
> >>>>> have shortened the discussion here.
> >>>>>
> >>>>
> >>>> That helper is also use today by nouveau so changing that name is not that
> >>>> easy it does require the multi-release dance. So i am not sure how much
> >>>> value there is in a name change.
> >>>>
> >>>
> >>> Once the dust settles, I would expect that a name change for this could go
> >>> via Andrew's tree, right? It seems incredible to claim that we've built something
> >>> that effectively does not allow any minor changes!
> >>>
> >>> I do think it's worth some *minor* trouble to improve the name, assuming that we
> >>> can do it in a simple patch, rather than some huge maintainer-level effort.
> >>
> >> Change to nouveau have to go through nouveau tree so changing name means:
> 
> Yes, I understand the guideline, but is that always how it must be done? Ben (+cc)?

Yes, it is not only about nouveau, it will be about every single
upstream driver using HMM. It is the easiest solution all other
solution involve coordination and/or risk of people that handle
the conflict to do something that break things.

Cheers,
Jérôme