Re: [PATCH 07/17] gup: Add gup_put_folio()

[John Hubbard <jhubbard@nvidia.com>]

On 1/2/22 13:57, Matthew Wilcox (Oracle) 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@infradead.org>
> ---
>   mm/gup.c | 44 +++++++++++++++-----------------------------
>   1 file changed, 15 insertions(+), 29 deletions(-)
> 

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


thanks,
-- 
John Hubbard
NVIDIA

> 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
> +	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);
>