linux-kernel - Re: [PATCH v2] orangefs: convert get_user_pages() --> pin_user

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Date:   Mon, 1 Jun 2020 07:13:53 -0400
From:   Mike Marshall <hubcap@...ibond.com>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Martin Brandenburg <martin@...ibond.com>,
        devel@...ts.orangefs.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v2] orangefs: convert get_user_pages() --> pin_user_pages()

Hi John.

Thanks for the patch, and the testing, and the reference to the
lwn article.

I have also applied your patch to 5.7-rc7 and have run xfstests.

I applied your patch to the orangefs for-next tree.

-Mike

On Sat, May 30, 2020 at 3:39 AM John Hubbard <jhubbard@...dia.com> wrote:
>
> On 2020-05-22 20:59, John Hubbard wrote:
> > This code was using get_user_pages*(), in a "Case 1" scenario
> > (Direct IO), using the categorization from [1]. That means that it's
> > time to convert the get_user_pages*() + put_page() calls to
> > pin_user_pages*() + unpin_user_pages() calls.
> >
> > There is some helpful background in [2]: basically, this is a small
> > part of fixing a long-standing disconnect between pinning pages, and
> > file systems' use of those pages.
> >
> > [1] Documentation/core-api/pin_user_pages.rst
> >
> > [2] "Explicit pinning of user-space pages":
> >      https://lwn.net/Articles/807108/
> >
> > Cc: Mike Marshall <hubcap@...ibond.com>
> > Cc: Martin Brandenburg <martin@...ibond.com>
> > Cc: devel@...ts.orangefs.org
> > Cc: linux-fsdevel@...r.kernel.org
> > Signed-off-by: John Hubbard <jhubbard@...dia.com>
> > ---
> >
> > Hi,
> >
> > Note that I have only compile-tested this patch, although that does
> > also include cross-compiling for a few other arches.
>
> An update on the run-time testing: Just now, I got basic orangefs tests
> running in xfstests, with this patch applied, and it all looks normal.
>
> thanks,
> --
> John Hubbard
> NVIDIA
>
> >
> > Changes since v1 [3]: correct the commit description, so that
> > it refers to "Case 1" instead of "Case 2".
> >
> >
> > [3] https://lore.kernel.org/r/20200518060139.2828423-1-jhubbard@nvidia.com
> >
> > thanks,
> > John Hubbard
> > NVIDIA
> >
> >   fs/orangefs/orangefs-bufmap.c | 9 +++------
> >   1 file changed, 3 insertions(+), 6 deletions(-)
> >
> > diff --git a/fs/orangefs/orangefs-bufmap.c b/fs/orangefs/orangefs-bufmap.c
> > index 2bb916d68576..538e839590ef 100644
> > --- a/fs/orangefs/orangefs-bufmap.c
> > +++ b/fs/orangefs/orangefs-bufmap.c
> > @@ -168,10 +168,7 @@ static DEFINE_SPINLOCK(orangefs_bufmap_lock);
> >   static void
> >   orangefs_bufmap_unmap(struct orangefs_bufmap *bufmap)
> >   {
> > -     int i;
> > -
> > -     for (i = 0; i < bufmap->page_count; i++)
> > -             put_page(bufmap->page_array[i]);
> > +     unpin_user_pages(bufmap->page_array, bufmap->page_count);
> >   }
> >
> >   static void
> > @@ -268,7 +265,7 @@ orangefs_bufmap_map(struct orangefs_bufmap *bufmap,
> >       int offset = 0, ret, i;
> >
> >       /* map the pages */
> > -     ret = get_user_pages_fast((unsigned long)user_desc->ptr,
> > +     ret = pin_user_pages_fast((unsigned long)user_desc->ptr,
> >                            bufmap->page_count, FOLL_WRITE, bufmap->page_array);
> >
> >       if (ret < 0)
> > @@ -280,7 +277,7 @@ orangefs_bufmap_map(struct orangefs_bufmap *bufmap,
> >
> >               for (i = 0; i < ret; i++) {
> >                       SetPageError(bufmap->page_array[i]);
> > -                     put_page(bufmap->page_array[i]);
> > +                     unpin_user_page(bufmap->page_array[i]);
> >               }
> >               return -ENOMEM;
> >       }
> >
>