linux-kernel - Re: [PATCH v3 06/25] mm: Add get

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Date:   Mon, 1 Mar 2021 16:45:57 -0500
From:   Zi Yan <ziy@...dia.com>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
CC:     <linux-fsdevel@...r.kernel.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 06/25] mm: Add get_folio

On 28 Jan 2021, at 2:03, Matthew Wilcox (Oracle) wrote:

> If we know we have a folio, we can call get_folio() instead of get_page()
> and save the overhead of calling compound_head().
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
>  include/linux/mm.h | 19 ++++++++++---------
>  1 file changed, 10 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 873d649107ba..d71c5776b571 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1192,18 +1192,19 @@ static inline bool is_pci_p2pdma_page(const struct page *page)
>  }
>
>  /* 127: arbitrary random number, small enough to assemble well */
> -#define page_ref_zero_or_close_to_overflow(page) \
> -	((unsigned int) page_ref_count(page) + 127u <= 127u)
> +#define folio_ref_zero_or_close_to_overflow(folio) \
> +	((unsigned int) page_ref_count(&folio->page) + 127u <= 127u)
> +
> +static inline void get_folio(struct folio *folio)
> +{
> +	/* Getting a page requires an already elevated page->_refcount. */
> +	VM_BUG_ON_FOLIO(folio_ref_zero_or_close_to_overflow(folio), folio);
> +	page_ref_inc(&folio->page);
> +}
>
>  static inline void get_page(struct page *page)
>  {
> -	page = compound_head(page);
> -	/*
> -	 * Getting a normal page or the head of a compound page
> -	 * requires to already have an elevated page->_refcount.
> -	 */
> -	VM_BUG_ON_PAGE(page_ref_zero_or_close_to_overflow(page), page);
> -	page_ref_inc(page);
> +	get_folio(page_folio(page));
>  }
>
>  bool __must_check try_grab_page(struct page *page, unsigned int flags);
> -- 
> 2.29.2

LGTM.

Reviewed-by: Zi Yan <ziy@...dia.com>

—
Best Regards,
Yan Zi

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