Messages in this thread Patch in this message | | | From | John Hubbard <> | Subject | [PATCH] mm/gup: documentation fix for pin_user_pages*() APIs | Date | Fri, 29 May 2020 01:45:15 -0700 |
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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, -- 2.26.2
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