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SubjectRe: [PATCH 16/75] mm/gup: Convert try_grab_page() to use a folio
From
On 2/4/22 11:57, Matthew Wilcox (Oracle) wrote:
> Hoist the folio conversion and the folio_ref_count() check to the
> top of the function instead of using the one buried in try_get_page().
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
> mm/gup.c | 28 +++++++++++++---------------
> 1 file changed, 13 insertions(+), 15 deletions(-)

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

thanks,
--
John Hubbard
NVIDIA

>
> diff --git a/mm/gup.c b/mm/gup.c
> index 4f1669db92f5..d18ce4da573f 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -174,15 +174,14 @@ static void put_compound_head(struct page *page, int refs, unsigned int flags)
>
> /**
> * try_grab_page() - elevate a page's refcount by a flag-dependent amount
> + * @page: pointer to page to be grabbed
> + * @flags: gup flags: these are the FOLL_* flag values.
> *
> * This might not do anything at all, depending on the flags argument.
> *
> * "grab" names in this file mean, "look at flags to decide whether to use
> * FOLL_PIN or FOLL_GET behavior, when incrementing the page's refcount.
> *
> - * @page: pointer to page to be grabbed
> - * @flags: gup flags: these are the FOLL_* flag values.
> - *
> * Either FOLL_PIN or FOLL_GET (or neither) may be set, but not both at the same
> * time. Cases: please see the try_grab_folio() documentation, with
> * "refs=1".
> @@ -193,29 +192,28 @@ static void put_compound_head(struct page *page, int refs, unsigned int flags)
> */
> bool __must_check try_grab_page(struct page *page, unsigned int flags)
> {
> + struct folio *folio = page_folio(page);
> +
> WARN_ON_ONCE((flags & (FOLL_GET | FOLL_PIN)) == (FOLL_GET | FOLL_PIN));
> + if (WARN_ON_ONCE(folio_ref_count(folio) <= 0))
> + return false;
>
> if (flags & FOLL_GET)
> - return try_get_page(page);
> + folio_ref_inc(folio);
> else if (flags & FOLL_PIN) {
> - page = compound_head(page);
> -
> - if (WARN_ON_ONCE(page_ref_count(page) <= 0))
> - return false;
> -
> /*
> - * Similar to try_grab_compound_head(): be sure to *also*
> + * Similar to try_grab_folio(): be sure to *also*
> * increment the normal page refcount field at least once,
> * so that the page really is pinned.
> */
> - if (PageHead(page)) {
> - page_ref_add(page, 1);
> - atomic_add(1, compound_pincount_ptr(page));
> + if (folio_test_large(folio)) {
> + folio_ref_add(folio, 1);
> + atomic_add(1, folio_pincount_ptr(folio));
> } else {
> - page_ref_add(page, GUP_PIN_COUNTING_BIAS);
> + folio_ref_add(folio, GUP_PIN_COUNTING_BIAS);
> }
>
> - mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_ACQUIRED, 1);
> + node_stat_mod_folio(folio, NR_FOLL_PIN_ACQUIRED, 1);
> }
>
> return true;

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