linux-kernel - Re: [PATCH v2 1/2] mm/gup.c: Don't pass gup_flags to check_and_migrate_movable

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Date:   Fri, 5 Aug 2022 00:35:08 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Alistair Popple <apopple@...dia.com>, linux-mm@...ck.org
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        "Sierra Guiza, Alejandro (Alex)" <alex.sierra@....com>,
        Chaitanya Kulkarni <kch@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Muchun Song <songmuchun@...edance.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH v2 1/2] mm/gup.c: Don't pass gup_flags to
 check_and_migrate_movable_pages()

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@...dia.com>


thanks,
-- 
John Hubbard
NVIDIA

> gup_flags.
> 
> Signed-off-by: Alistair Popple <apopple@...dia.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