linux-kernel - Re: [PATCH v2 13/28] mm: Add folio_pincount

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Date:   Mon, 10 Jan 2022 20:22:10 -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 13/28] mm: Add folio_pincount_ptr()

On 1/9/22 20:23, Matthew Wilcox (Oracle) wrote:
> This is the folio equivalent of compound_pincount_ptr().
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
>   include/linux/mm_types.h | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 60e4595eaf63..34c7114ea9e9 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -312,6 +312,12 @@ static inline atomic_t *compound_mapcount_ptr(struct page *page)
>   	return &page[1].compound_mapcount;
>   }
>   
> +static inline atomic_t *folio_pincount_ptr(struct folio *folio)
> +{
> +	struct page *tail = &folio->page + 1;
> +	return &tail->compound_pincount;
> +}
> +

Should we make this code (the various folio map/pin count inline
functions) more uniform? I see that you prefer "+1" over page[1], sure,
but having a mix seems like it's trying to call out a difference for
which the reader would search in vain. :)

After the whole series is applied, this area ends up with a 50/50 mix of the
two.

Or am I overlooking something, and they really *should* look different?


Just a very minor point, so either way,

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

thanks,
-- 
John Hubbard
NVIDIA

>   static inline atomic_t *compound_pincount_ptr(struct page *page)
>   {
>   	return &page[1].compound_pincount;