Comment inline.
> On Jan 2, 2022, at 2:57 PM, Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> wrote:
>
> put_compound_head() is turned into a call to gup_put_folio().
> This removes the last call to put_page_refs(), so delete it.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> ---
> mm/gup.c | 44 +++++++++++++++-----------------------------
> 1 file changed, 15 insertions(+), 29 deletions(-)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index 58e5cfaaa676..6d827f7d66d8 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -36,29 +36,11 @@ static void folio_pincount_add(struct folio *folio, int refs)
> atomic_add(refs, folio_pincount_ptr(folio));
> }
>
> -static void hpage_pincount_sub(struct page *page, int refs)
> +static void folio_pincount_sub(struct folio *folio, int refs)
> {
> - VM_BUG_ON_PAGE(!hpage_pincount_available(page), page);
> - VM_BUG_ON_PAGE(page != compound_head(page), page);
> -
> - atomic_sub(refs, compound_pincount_ptr(page));
> -}
> -
> -/* Equivalent to calling put_page() @refs times. */
> -static void put_page_refs(struct page *page, int refs)
> -{
> -#ifdef CONFIG_DEBUG_VM
> - if (VM_WARN_ON_ONCE_PAGE(page_ref_count(page) < refs, page))
> - return;
> -#endif
Should this retain a form of the CONFIG_DEBUG_VM warning here to trigger if
folio_pincount_ptr(folio) is < refs?
> + VM_BUG_ON_FOLIO(!folio_pincount_available(folio), folio);
> - /*
> - * Calling put_page() for each ref is unnecessarily slow. Only the last
> - * ref needs a put_page().
> - */
> - if (refs > 1)
> - page_ref_sub(page, refs - 1);
> - put_page(page);
> + atomic_sub(refs, folio_pincount_ptr(folio));
> }
>
> /*
> @@ -175,19 +157,23 @@ struct page *try_grab_compound_head(struct page *page,
> return NULL;
> }
>
> -static void put_compound_head(struct page *page, int refs, unsigned int flags)
> +static void gup_put_folio(struct folio *folio, int refs, unsigned int flags)
> {
> if (flags & FOLL_PIN) {
> - mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED,
> - refs);
> -
> - if (hpage_pincount_available(page))
> - hpage_pincount_sub(page, refs);
> + node_stat_mod_folio(folio, NR_FOLL_PIN_RELEASED, refs);
> + if (folio_pincount_available(folio))
> + folio_pincount_sub(folio, refs);
> else
> refs *= GUP_PIN_COUNTING_BIAS;
> }
>
> - put_page_refs(page, refs);
> + folio_put_refs(folio, refs);
> +}
> +
> +static void put_compound_head(struct page *page, int refs, unsigned int flags)
> +{
> + VM_BUG_ON_PAGE(PageTail(page), page);
> + gup_put_folio((struct folio *)page, refs, flags);
> }
>
> /**
> @@ -228,7 +214,7 @@ bool __must_check try_grab_page(struct page *page, unsigned int flags)
> */
> void unpin_user_page(struct page *page)
> {
> - put_compound_head(compound_head(page), 1, FOLL_PIN);
> + gup_put_folio(page_folio(page), 1, FOLL_PIN);
> }
> EXPORT_SYMBOL(unpin_user_page);
>
> --
> 2.33.0
>
>
