linux-kernel - Re: [PATCH] mm/gup: documentation fix for pin_user

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Message-ID: <CAFqt6za3N3gyDvEdoQb5d6_p-Ri_DGM=+eVv+wfQMadNn7g5tQ@mail.gmail.com>
Date:   Sun, 31 May 2020 12:21:05 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     John Hubbard <jhubbard@...dia.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Jan Kara <jack@...e.cz>, Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH] mm/gup: documentation fix for pin_user_pages*() APIs

On Fri, May 29, 2020 at 2:41 PM David Hildenbrand <david@...hat.com> wrote:
>
> On 29.05.20 10:45, John Hubbard wrote:
> > All of the pin_user_pages*() API calls will cause pages to be
> > dma-pinned. As such, they are all suitable for either DMA, RDMA,
> > and/or Direct IO. The documentation should say so, but it was
> > instead saying that three of the API calls were only suitable for
> > Direct IO. This was discovered when a reviewer wondered why an
> > API call that specifically recommended against Case 2 (DMA/RDMA)
> > was being used in a DMA situation [1].
> >
> > Fix this by simply deleting those claims. The gup.c comments already
> > refer to the more extensive Documentation/core-api/pin_user_pages.rst,
> > which does have the correct guidance. So let's just write it once,
> > there.
> >
> > [1] https://lore.kernel.org/r/20200529074658.GM30374@kadam
> >
> > Cc: Dan Carpenter <dan.carpenter@...cle.com>
> > Cc: Jan Kara <jack@...e.cz>
> > Cc: Vlastimil Babka <vbabka@...e.cz>
> > Signed-off-by: John Hubbard <jhubbard@...dia.com>
> > ---
> >
> > Hi,
> >
> > This applies on top of linux-next, in order to avoid a conflict with
> > Mauro Carvalho Chehab's fix to the lines right above these.
> >
> > thanks,
> > John Hubbard
> > NVIDIA
> >
> >
> >  mm/gup.c | 9 ---------
> >  1 file changed, 9 deletions(-)
> >
> > diff --git a/mm/gup.c b/mm/gup.c
> > index ee039d421746d..311d0f11b35e6 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -2875,9 +2875,6 @@ EXPORT_SYMBOL_GPL(get_user_pages_fast);
> >   *
> >   * FOLL_PIN means that the pages must be released via unpin_user_page(). Please
> >   * see Documentation/core-api/pin_user_pages.rst for further details.
> > - *
> > - * This is intended for Case 1 (DIO) in Documentation/core-api/pin_user_pages.rst. It
> > - * is NOT intended for Case 2 (RDMA: long-term pins).
> >   */
> >  int pin_user_pages_fast(unsigned long start, int nr_pages,
> >                       unsigned int gup_flags, struct page **pages)
> > @@ -2951,9 +2948,6 @@ EXPORT_SYMBOL_GPL(pin_user_pages_fast_only);
> >   *
> >   * FOLL_PIN means that the pages must be released via unpin_user_page(). Please
> >   * see Documentation/core-api/pin_user_pages.rst for details.
> > - *
> > - * This is intended for Case 1 (DIO) in Documentation/core-api/pin_user_pages.rst. It
> > - * is NOT intended for Case 2 (RDMA: long-term pins).
> >   */
> >  long pin_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
> >                          unsigned long start, unsigned long nr_pages,
> > @@ -2987,9 +2981,6 @@ EXPORT_SYMBOL(pin_user_pages_remote);
> >   *
> >   * FOLL_PIN means that the pages must be released via unpin_user_page(). Please
> >   * see Documentation/core-api/pin_user_pages.rst for details.
> > - *
> > - * This is intended for Case 1 (DIO) in Documentation/core-api/pin_user_pages.rst. It
> > - * is NOT intended for Case 2 (RDMA: long-term pins).
> >   */
> >  long pin_user_pages(unsigned long start, unsigned long nr_pages,
> >                   unsigned int gup_flags, struct page **pages,
> >
>
> Reviewed-by: David Hildenbrand <david@...hat.com>

Acked-by : Souptick Joarder <jrdr.linux@...il.com>

>
> --
> Thanks,
>
> David / dhildenb
>