| Message ID | 20200529084515.46259-1-jhubbard@nvidia.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm/gup: documentation fix for pin_user_pages*() APIs | expand |
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@oracle.com> > Cc: Jan Kara <jack@suse.cz> > Cc: Vlastimil Babka <vbabka@suse.cz> > Signed-off-by: John Hubbard <jhubbard@nvidia.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@redhat.com>
On Fri, May 29, 2020 at 2:41 PM David Hildenbrand <david@redhat.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@oracle.com> > > Cc: Jan Kara <jack@suse.cz> > > Cc: Vlastimil Babka <vbabka@suse.cz> > > Signed-off-by: John Hubbard <jhubbard@nvidia.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@redhat.com> Acked-by : Souptick Joarder <jrdr.linux@gmail.com> > > -- > Thanks, > > David / dhildenb >
Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
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,
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@oracle.com> Cc: Jan Kara <jack@suse.cz> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: John Hubbard <jhubbard@nvidia.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(-)