From: John Hubbard <jhubbard@nvidia.com>
To: Daniel Vetter <daniel.vetter@ffwll.ch>,
DRI Development <dri-devel@lists.freedesktop.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
"Daniel Vetter" <daniel.vetter@intel.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Jérôme Glisse" <jglisse@redhat.com>, "Jan Kara" <jack@suse.cz>,
"Dan Williams" <dan.j.williams@intel.com>,
linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org,
linux-samsung-soc@vger.kernel.org, linux-media@vger.kernel.org
Subject: Re: [PATCH 2/2] mm/frame-vec: use FOLL_LONGTERM
Date: Fri, 2 Oct 2020 15:39:18 -0700 [thread overview]
Message-ID: <cb56763e-4fda-a783-03ae-7f749ec55981@nvidia.com> (raw)
In-Reply-To: <20201002175303.390363-2-daniel.vetter@ffwll.ch>
On 10/2/20 10:53 AM, Daniel Vetter wrote:
> For $reasons I've stumbled over this code and I'm not sure the change
> to the new gup functions in 55a650c35fea ("mm/gup: frame_vector:
> convert get_user_pages() --> pin_user_pages()") was entirely correct.
>
> This here is used for long term buffers (not just quick I/O) like
> RDMA, and John notes this in his patch. But I thought the rule for
> these is that they need to add FOLL_LONGTERM, which John's patch
> didn't do.
Yep. The earlier gup --> pup conversion patches were intended to not
have any noticeable behavior changes, and FOLL_LONGTERM, with it's
special cases and such, added some risk that I wasn't ready to take
on yet. Also, FOLL_LONGTERM rules are only *recently* getting firmed
up. So there was some doubt at least in my mind, about which sites
should have it.
But now that we're here, I think it's really good that you've brought
this up. It's definitely time to add FOLL_LONGTERM wherever it's missing.
thanks,
--
John Hubbard
NVIDIA
>
> There is already a dax specific check (added in b7f0554a56f2 ("mm:
> fail get_vaddr_frames() for filesystem-dax mappings")), so this seems
> like the prudent thing to do.
>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Cc: Jérôme Glisse <jglisse@redhat.com>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: linux-mm@kvack.org
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-samsung-soc@vger.kernel.org
> Cc: linux-media@vger.kernel.org
> ---
> Hi all,
>
> I stumbled over this and figured typing this patch can't hurt. Really
> just to maybe learn a few things about how gup/pup is supposed to be
> used (we have a bit of that in drivers/gpu), this here isn't really
> ralated to anything I'm doing.
>
> I'm also wondering whether the explicit dax check should be removed,
> since FOLL_LONGTERM should take care of that already.
> -Daniel
> ---
> mm/frame_vector.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/frame_vector.c b/mm/frame_vector.c
> index 5d34c9047e9c..3507e09cb3ff 100644
> --- a/mm/frame_vector.c
> +++ b/mm/frame_vector.c
> @@ -35,7 +35,7 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
> {
> struct mm_struct *mm = current->mm;
> struct vm_area_struct *vma;
> - unsigned int gup_flags = FOLL_WRITE | FOLL_FORCE;
> + unsigned int gup_flags = FOLL_WRITE | FOLL_FORCE | FOLL_LONGTERM;
> int ret = 0;
> int err;
> int locked;
>
next prev parent reply other threads:[~2020-10-02 22:39 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-02 17:53 [PATCH 1/2] mm/frame-vec: Drop gup_flags from get_vaddr_frames() Daniel Vetter
2020-10-02 17:53 ` [PATCH 2/2] mm/frame-vec: use FOLL_LONGTERM Daniel Vetter
2020-10-02 18:06 ` Jason Gunthorpe
2020-10-02 18:16 ` Daniel Vetter
2020-10-02 23:31 ` Jason Gunthorpe
2020-10-03 8:34 ` Oded Gabbay
2020-10-03 9:40 ` Daniel Vetter
2020-10-04 12:50 ` Jason Gunthorpe
2020-10-04 16:09 ` Daniel Vetter
2020-10-05 17:28 ` Jason Gunthorpe
2020-10-05 18:16 ` Daniel Vetter
2020-10-05 18:37 ` Jason Gunthorpe
2020-10-05 18:54 ` Daniel Vetter
2020-10-05 22:43 ` Daniel Vetter
2020-10-05 23:41 ` Jason Gunthorpe
2020-10-06 6:23 ` Daniel Vetter
2020-10-06 12:26 ` Jason Gunthorpe
2020-10-06 13:08 ` Daniel Vetter
2020-10-07 10:47 ` Marek Szyprowski
2020-10-07 12:01 ` Daniel Vetter
2020-10-07 12:33 ` Marek Szyprowski
2020-10-07 12:44 ` Jason Gunthorpe
2020-10-07 12:47 ` Tomasz Figa
2020-10-07 12:58 ` Daniel Vetter
2020-10-07 13:06 ` Jason Gunthorpe
2020-10-07 13:34 ` Tomasz Figa
2020-10-07 13:42 ` Jason Gunthorpe
2020-10-07 14:08 ` Daniel Vetter
2020-10-07 14:11 ` Tomasz Figa
2020-10-07 14:22 ` Daniel Vetter
2020-10-07 15:05 ` Tomasz Figa
2020-10-07 14:58 ` Jason Gunthorpe
2020-10-07 13:06 ` Tomasz Figa
2020-10-07 13:14 ` Jason Gunthorpe
2020-10-05 15:03 ` Jan Kara
2020-10-02 22:39 ` John Hubbard [this message]
2020-10-03 9:45 ` Daniel Vetter
2020-10-03 22:52 ` John Hubbard
2020-10-03 23:24 ` Jason Gunthorpe
2020-10-04 11:20 ` Daniel Vetter
2020-10-05 17:35 ` Jason Gunthorpe
2020-10-02 18:22 ` [PATCH 1/2] mm/frame-vec: Drop gup_flags from get_vaddr_frames() Tomasz Figa
2020-10-02 19:21 ` Oded Gabbay
2020-10-05 17:38 [PATCH 2/2] mm/frame-vec: use FOLL_LONGTERM Jason Gunthorpe
2020-10-05 17:47 ` Jason Gunthorpe
2020-10-06 3:36 ` Andrew Morton
2020-10-06 11:57 ` Jason Gunthorpe
2020-10-05 17:53 ` Jan Kara
2020-10-05 17:57 ` Jason Gunthorpe
2020-10-05 18:16 ` Daniel Vetter
2020-10-06 11:56 ` Daniel Vetter
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