linux-kernel - Re: [PATCH v2 14/28] mm: Convert page_maybe_dma

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Date:   Mon, 10 Jan 2022 20:27:16 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>, linux-mm@...ck.org
Cc:     Christoph Hellwig <hch@...radead.org>,
        William Kucharski <william.kucharski@...cle.com>,
        linux-kernel@...r.kernel.org, Jason Gunthorpe <jgg@...pe.ca>
Subject: Re: [PATCH v2 14/28] mm: Convert page_maybe_dma_pinned() to use a
 folio

On 1/9/22 20:23, Matthew Wilcox (Oracle) wrote:
> Replace three calls to compound_head() with one.  This removes the last
> user of compound_pincount(), so remove that helper too.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
>   include/linux/mm.h | 21 ++++++++-------------
>   1 file changed, 8 insertions(+), 13 deletions(-)

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


thanks,
-- 
John Hubbard
NVIDIA

> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index bf9624ca61c3..d3769897c8ac 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -934,13 +934,6 @@ static inline int head_compound_pincount(struct page *head)
>   	return atomic_read(compound_pincount_ptr(head));
>   }
>   
> -static inline int compound_pincount(struct page *page)
> -{
> -	VM_BUG_ON_PAGE(!PageCompound(page), page);
> -	page = compound_head(page);
> -	return head_compound_pincount(page);
> -}
> -
>   static inline void set_compound_order(struct page *page, unsigned int order)
>   {
>   	page[1].compound_order = order;
> @@ -1340,18 +1333,20 @@ void unpin_user_pages(struct page **pages, unsigned long npages);
>    */
>   static inline bool page_maybe_dma_pinned(struct page *page)
>   {
> -	if (PageCompound(page))
> -		return compound_pincount(page) > 0;
> +	struct folio *folio = page_folio(page);
> +
> +	if (folio_test_large(folio))
> +		return atomic_read(folio_pincount_ptr(folio)) > 0;
>   
>   	/*
> -	 * page_ref_count() is signed. If that refcount overflows, then
> -	 * page_ref_count() returns a negative value, and callers will avoid
> +	 * folio_ref_count() is signed. If that refcount overflows, then
> +	 * folio_ref_count() returns a negative value, and callers will avoid
>   	 * further incrementing the refcount.
>   	 *
> -	 * Here, for that overflow case, use the signed bit to count a little
> +	 * Here, for that overflow case, use the sign bit to count a little
>   	 * bit higher via unsigned math, and thus still get an accurate result.
>   	 */
> -	return ((unsigned int)page_ref_count(compound_head(page))) >=
> +	return ((unsigned int)folio_ref_count(folio)) >=
>   		GUP_PIN_COUNTING_BIAS;
>   }
>