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SubjectRe: [PATCH v2 1/2] mm/gup.c: Don't pass gup_flags to check_and_migrate_movable_pages()
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On 8/4/22 23:29, Alistair Popple wrote:
> gup_flags is passed to check_and_migrate_movable_pages() so that it can
> call either put_page() or unpin_user_page() to drop the page reference.
> However check_and_migrate_movable_pages() is only called for
> FOLL_LONGTERM, which implies FOLL_PIN so there is no need to pass

heh, while verifying the above claim, I noticed that
__gup_longterm_locked() has been misnamed for some time now. That
function handles both FOLL_LONGTERM and !FOLL_LONGTERM. There's
always something...

Anyway, though, this patch is a good cleanup step, so:

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


thanks,
--
John Hubbard
NVIDIA

> gup_flags.
>
> Signed-off-by: Alistair Popple <apopple@nvidia.com>
> ---
> mm/gup.c | 21 ++++++++-------------
> 1 file changed, 8 insertions(+), 13 deletions(-)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index c6d060d..e26ccc0 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1907,8 +1907,7 @@ struct page *get_dump_page(unsigned long addr)
> * Return negative error if migration fails.
> */
> static long check_and_migrate_movable_pages(unsigned long nr_pages,
> - struct page **pages,
> - unsigned int gup_flags)
> + struct page **pages)
> {
> unsigned long isolation_error_count = 0, i;
> struct folio *prev_folio = NULL;
> @@ -1941,10 +1940,8 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages,
> * Migration will fail if the page is pinned, so convert
> * the pin on the source page to a normal reference.
> */
> - if (gup_flags & FOLL_PIN) {
> - get_page(&folio->page);
> - unpin_user_page(&folio->page);
> - }
> + get_page(&folio->page);
> + unpin_user_page(&folio->page);
>
> ret = migrate_device_coherent_page(&folio->page);
> if (ret)
> @@ -1998,10 +1995,7 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages,
> if (!pages[i])
> continue;
>
> - if (gup_flags & FOLL_PIN)
> - unpin_user_page(pages[i]);
> - else
> - put_page(pages[i]);
> + unpin_user_page(pages[i]);
> }
>
> if (!list_empty(&movable_page_list)) {
> @@ -2023,8 +2017,7 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages,
> }
> #else
> static long check_and_migrate_movable_pages(unsigned long nr_pages,
> - struct page **pages,
> - unsigned int gup_flags)
> + struct page **pages)
> {
> return nr_pages;
> }
> @@ -2053,7 +2046,9 @@ static long __gup_longterm_locked(struct mm_struct *mm,
> NULL, gup_flags);
> if (rc <= 0)
> break;
> - rc = check_and_migrate_movable_pages(rc, pages, gup_flags);
> +
> + WARN_ON_ONCE(!(gup_flags & FOLL_PIN));
> + rc = check_and_migrate_movable_pages(rc, pages);
> } while (!rc);
> memalloc_pin_restore(flags);
>
>
> base-commit: 360614c01f81f48a89d8b13f8fa69c3ae0a1f5c7

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