netdev - Re: [PATCH v3 00/23] mm/gup: track dma-pinned pages: FOLL_PIN, FOLL

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Message-ID: <283b121d-f526-f43f-de45-dc2f8318d860@nvidia.com>
Date:   Wed, 13 Nov 2019 12:28:02 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Jan Kara <jack@...e.cz>, Jason Gunthorpe <jgg@...pe.ca>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Alex Williamson <alex.williamson@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        David Airlie <airlied@...ux.ie>,
        "David S . Miller" <davem@...emloft.net>,
        Ira Weiny <ira.weiny@...el.com>, Jens Axboe <axboe@...nel.dk>,
        Jonathan Corbet <corbet@....net>,
        Jérôme Glisse <jglisse@...hat.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michal Hocko <mhocko@...e.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Paul Mackerras <paulus@...ba.org>,
        Shuah Khan <shuah@...nel.org>,
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Subject: Re: [PATCH v3 00/23] mm/gup: track dma-pinned pages: FOLL_PIN,
 FOLL_LONGTERM

On 11/13/19 3:43 AM, Daniel Vetter wrote:
...
>>>> Can't we call this unpin_user_page then, for some symmetry? Or is that
>>>> even more churn?
>>>>
>>>> Looking from afar the naming here seems really confusing.
>>>
>>>
>>> That look from afar is valuable, because I'm too close to the problem to see
>>> how the naming looks. :)
>>>
>>> unpin_user_page() sounds symmetrical. It's true that it would cause more
>>> churn (which is why I started off with a proposal that avoids changing the
>>> names of put_user_page*() APIs). But OTOH, the amount of churn is proportional
>>> to the change in direction here, and it's really only 10 or 20 lines changed,
>>> in the end.
>>>
>>> So I'm open to changing to that naming. It would be nice to hear what others
>>> prefer, too...
>>
>> FWIW I'd find unpin_user_page() also better than put_user_page() as a
>> counterpart to pin_user_pages().
> 
> One more point from afar on pin/unpin: We use that a lot in graphics for
> permanently pinned graphics buffer objects. Which really only should be
> used for scanout. So at least graphics folks should have an appropriate
> mindset and try to make sure we don't overuse this stuff.
> -Daniel
> 

OK, Ira also likes "unpin", and so far no one has said *anything* in favor
of the "put_user_page" names, so I think we have a winner! I'll change the
names to unpin_user_page*().


thanks,
-- 
John Hubbard
NVIDIA