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: <20190329014259.GD16680@redhat.com>
Date:   Thu, 28 Mar 2019 21:42:59 -0400
From:   Jerome Glisse <jglisse@...hat.com>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     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 06:30:26PM -0700, John Hubbard wrote:
> On 3/28/19 6:17 PM, Jerome Glisse wrote:
> > On Thu, Mar 28, 2019 at 09:42:31AM -0700, Ira Weiny wrote:
> >> On Thu, Mar 28, 2019 at 04:28:47PM -0700, John Hubbard wrote:
> >>> On 3/28/19 4:21 PM, Jerome Glisse wrote:
> >>>> On Thu, Mar 28, 2019 at 03:40:42PM -0700, John Hubbard wrote:
> >>>>> On 3/28/19 3:31 PM, Jerome Glisse wrote:
> >>>>>> On Thu, Mar 28, 2019 at 03:19:06PM -0700, John Hubbard wrote:
> >>>>>>> On 3/28/19 3:12 PM, Jerome Glisse wrote:
> >>>>>>>> On Thu, Mar 28, 2019 at 02:59:50PM -0700, John Hubbard wrote:
> >>>>>>>>> On 3/25/19 7:40 AM, jglisse@...hat.com wrote:
> >>>>>>>>>> From: Jérôme Glisse <jglisse@...hat.com>
> >>> [...]
> >> 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:
 -  release N add function with new name, maybe make the old function just
    a wrapper to the new function
 -  release N+1 update user to use the new name
 -  release N+2 remove the old name

So it is do-able but it is painful so i rather do that one latter that now
as i am sure people will then complain again about some little thing and it
will post pone this whole patchset on that new bit. To avoid post-poning
RDMA and bunch of other patchset that build on top of that i rather get
this patchset in and then do more changes in the next cycle.

This is just a capacity thing.

Cheers,
Jérôme