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

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Message-ID: <20191112203802.GD5584@ziepe.ca>
Date:   Tue, 12 Nov 2019 16:38:02 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     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>,
        Daniel Vetter <daniel@...ll.ch>,
        Dave Chinner <david@...morbit.com>,
        David Airlie <airlied@...ux.ie>,
        "David S . Miller" <davem@...emloft.net>,
        Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        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>,
        Vlastimil Babka <vbabka@...e.cz>, bpf@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, kvm@...r.kernel.org,
        linux-block@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-media@...r.kernel.org, linux-rdma@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, netdev@...r.kernel.org,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 00/23] mm/gup: track dma-pinned pages: FOLL_PIN,
 FOLL_LONGTERM

On Mon, Nov 11, 2019 at 04:06:37PM -0800, John Hubbard wrote:
> Hi,
> 
> The cover letter is long, so the more important stuff is first:
> 
> * Jason, if you or someone could look at the the VFIO cleanup (patch 8)
>   and conversion to FOLL_PIN (patch 18), to make sure it's use of
>   remote and longterm gup matches what we discussed during the review
>   of v2, I'd appreciate it.
> 
> * Also for Jason and IB: as noted below, in patch 11, I am (too?) boldly
>   converting from put_user_pages() to release_pages().

Why are we doing this? I think things got confused here someplace, as
the comment still says:

/**
 * put_user_page() - release a gup-pinned page
 * @page:            pointer to page to be released
 *
 * Pages that were pinned via get_user_pages*() must be released via
 * either put_user_page(), or one of the put_user_pages*() routines
 * below.

I feel like if put_user_pages() is not the correct way to undo
get_user_pages() then it needs to be deleted.

Jason