linux-kernel - Re: [PATCH v2 02/11] mm/hmm: use reference counting for HMM struct v2

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Message-ID: <20190329022217.GI16680@redhat.com>
Date:   Thu, 28 Mar 2019 22:22:18 -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 02/11] mm/hmm: use reference counting for HMM struct v2

On Thu, Mar 28, 2019 at 07:11:17PM -0700, John Hubbard wrote:
> On 3/28/19 6:50 PM, Jerome Glisse wrote:
> [...]
> >>>
> >>> The hmm_put() is just releasing the reference on the hmm struct.
> >>>
> >>> Here i feel i am getting contradicting requirement from different people.
> >>> I don't think there is a way to please everyone here.
> >>>
> >>
> >> That's not a true conflict: you're comparing your actual implementation
> >> to Ira's request, rather than comparing my request to Ira's request.
> >>
> >> I think there's a way forward. Ira and I are actually both asking for the
> >> same thing:
> >>
> >> a) clear, concise get/put routines
> >>
> >> b) avoiding odd side effects in functions that have one name, but do
> >> additional surprising things.
> > 
> > Please show me code because i do not see any other way to do it then
> > how i did.
> > 
> 
> Sure, I'll take a run at it. I've driven you crazy enough with the naming 
> today, it's time to back it up with actual code. :)

Note that every single line in mm_get_hmm() do matter.

> I hope this is not one of those "we must also change Nouveau in N+M steps" 
> situations, though. I'm starting to despair about reviewing code that
> basically can't be changed...

It can be change but i rather not do too many in one go, each change is
like a tango with one partner and having tango with multiple partner at
once is painful much more likely to step on each other foot.

Cheers,
Jérôme