Re: [RFC PATCH v2 12/19] mm/gup: Prep put_user_pages() to take an vaddr_pin struct

John Hubbard
2019-08-10T00:30:07Z

On 8/9/19 3:58 PM, ira.weiny@intel.com wrote:
> From: Ira Weiny <ira.weiny@intel.com>
>
> Once callers start to use vaddr_pin the put_user_pages calls will need
> to have access to this data coming in. Prep put_user_pages() for this
> data.
>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> ---
> include/linux/mm.h | 20 +-------
> mm/gup.c | 122 ++++++++++++++++++++++++++++++++-------------
> 2 files changed, 88 insertions(+), 54 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index befe150d17be..9d37cafbef9a 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1064,25 +1064,7 @@ static inline void put_page(struct page *page)
> __put_page(page);
> }
>
> -/**
> - * put_user_page() - release a gup-pinned page
> - * @page: pointer to page to be released
> - *
> - * Pages that were pinned via get_user_pages*() must be released via
> - * either put_user_page(), or one of the put_user_pages*() routines
> - * below. This is so that eventually, pages that are pinned via
> - * get_user_pages*() can be separately tracked and uniquely handled. In
> - * particular, interactions with RDMA and filesystems need special
> - * handling.
> - *
> - * put_user_page() and put_page() are not interchangeable, despite this early
> - * implementation that makes them look the same. put_user_page() calls must
> - * be perfectly matched up with get_user_page() calls.
> - */
> -static inline void put_user_page(struct page *page)
> -{
> - put_page(page);
> -}
> +void put_user_page(struct page *page);
>
> void put_user_pages_dirty_lock(struct page **pages, unsigned long npages,
> bool make_dirty);
> diff --git a/mm/gup.c b/mm/gup.c
> index a7a9d2f5278c..10cfd30ff668 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -24,30 +24,41 @@
>
> #include "internal.h"
>
> -/**
> - * put_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages
> - * @pages: array of pages to be maybe marked dirty, and definitely released.

A couple comments from our circular review chain: some fellow with the same
last name as you, recommended wording it like this:

@pages: array of pages to be put

> - * @npages: number of pages in the @pages array.
> - * @make_dirty: whether to mark the pages dirty
> - *
> - * "gup-pinned page" refers to a page that has had one of the get_user_pages()
> - * variants called on that page.
> - *
> - * For each page in the @pages array, make that page (or its head page, if a
> - * compound page) dirty, if @make_dirty is true, and if the page was previously
> - * listed as clean. In any case, releases all pages using put_user_page(),
> - * possibly via put_user_pages(), for the non-dirty case.
> - *
> - * Please see the put_user_page() documentation for details.
> - *
> - * set_page_dirty_lock() is used internally. If instead, set_page_dirty() is
> - * required, then the caller should a) verify that this is really correct,
> - * because _lock() is usually required, and b) hand code it:
> - * set_page_dirty_lock(), put_user_page().
> - *
> - */
> -void put_user_pages_dirty_lock(struct page **pages, unsigned long npages,
> - bool make_dirty)
> +static void __put_user_page(struct vaddr_pin *vaddr_pin, struct page *page)
> +{
> + page = compound_head(page);
> +
> + /*
> + * For devmap managed pages we need to catch refcount transition from
> + * GUP_PIN_COUNTING_BIAS to 1, when refcount reach one it means the
> + * page is free and we need to inform the device driver through
> + * callback. See include/linux/memremap.h and HMM for details.
> + */
> + if (put_devmap_managed_page(page))
> + return;
> +
> + if (put_page_testzero(page))
> + __put_page(page);
> +}
> +
> +static void __put_user_pages(struct vaddr_pin *vaddr_pin, struct page **pages,
> + unsigned long npages)
> +{
> + unsigned long index;
> +
> + /*
> + * TODO: this can be optimized for huge pages: if a series of pages is
> + * physically contiguous and part of the same compound page, then a
> + * single operation to the head page should suffice.
> + */

As discussed in the other review thread (""), let's just delete that comment,
as long as you're moving things around.

> + for (index = 0; index < npages; index++)
> + __put_user_page(vaddr_pin, pages[index]);
> +}
> +
> +static void __put_user_pages_dirty_lock(struct vaddr_pin *vaddr_pin,
> + struct page **pages,
> + unsigned long npages,
> + bool make_dirty)

Elsewhere in this series, we pass vaddr_pin at the end of the arg list.
Here we pass it at the beginning, and it caused a minor jar when reading it.
Obviously just bike shedding at this point, though. Either way. :)

> {
> unsigned long index;
>
> @@ -58,7 +69,7 @@ void put_user_pages_dirty_lock(struct page **pages, unsigned long npages,
> */
>
> if (!make_dirty) {
> - put_user_pages(pages, npages);
> + __put_user_pages(vaddr_pin, pages, npages);
> return;
> }
>
> @@ -86,9 +97,58 @@ void put_user_pages_dirty_lock(struct page **pages, unsigned long npages,
> */
> if (!PageDirty(page))
> set_page_dirty_lock(page);
> - put_user_page(page);
> + __put_user_page(vaddr_pin, page);
> }
> }
> +
> +/**
> + * put_user_page() - release a gup-pinned page
> + * @page: pointer to page to be released
> + *
> + * Pages that were pinned via get_user_pages*() must be released via
> + * either put_user_page(), or one of the put_user_pages*() routines
> + * below. This is so that eventually, pages that are pinned via
> + * get_user_pages*() can be separately tracked and uniquely handled. In
> + * particular, interactions with RDMA and filesystems need special
> + * handling.
> + *
> + * put_user_page() and put_page() are not interchangeable, despite this early
> + * implementation that makes them look the same. put_user_page() calls must
> + * be perfectly matched up with get_user_page() calls.
> + */
> +void put_user_page(struct page *page)
> +{
> + __put_user_page(NULL, page);
> +}
> +EXPORT_SYMBOL(put_user_page);
> +
> +/**
> + * put_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages
> + * @pages: array of pages to be maybe marked dirty, and definitely released.

Same here:

@pages: array of pages to be put

> + * @npages: number of pages in the @pages array.
> + * @make_dirty: whether to mark the pages dirty
> + *
> + * "gup-pinned page" refers to a page that has had one of the get_user_pages()
> + * variants called on that page.
> + *
> + * For each page in the @pages array, make that page (or its head page, if a
> + * compound page) dirty, if @make_dirty is true, and if the page was previously
> + * listed as clean. In any case, releases all pages using put_user_page(),
> + * possibly via put_user_pages(), for the non-dirty case.
> + *
> + * Please see the put_user_page() documentation for details.
> + *
> + * set_page_dirty_lock() is used internally. If instead, set_page_dirty() is
> + * required, then the caller should a) verify that this is really correct,
> + * because _lock() is usually required, and b) hand code it:
> + * set_page_dirty_lock(), put_user_page().
> + *
> + */
> +void put_user_pages_dirty_lock(struct page **pages, unsigned long npages,
> + bool make_dirty)
> +{
> + __put_user_pages_dirty_lock(NULL, pages, npages, make_dirty);
> +}
> EXPORT_SYMBOL(put_user_pages_dirty_lock);
>
> /**
> @@ -102,15 +162,7 @@ EXPORT_SYMBOL(put_user_pages_dirty_lock);
> */
> void put_user_pages(struct page **pages, unsigned long npages)
> {
> - unsigned long index;
> -
> - /*
> - * TODO: this can be optimized for huge pages: if a series of pages is
> - * physically contiguous and part of the same compound page, then a
> - * single operation to the head page should suffice.
> - */
> - for (index = 0; index < npages; index++)
> - put_user_page(pages[index]);
> + __put_user_pages(NULL, pages, npages);
> }
> EXPORT_SYMBOL(put_user_pages);
>
>

This all looks pretty good, so regardless of the outcome of the minor
points above,

Reviewed-by: John Hubbard <jhubbard@nvidia.com>

thanks,
--
John Hubbard
NVIDIA