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Subject: Re: [PATCH v10 07/33] mm: Add folio_get
To:     "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        akpm@linux-foundation.org
Cc:     linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Zi Yan <ziy@nvidia.com>,
        Christoph Hellwig <hch@lst.de>,
        Jeff Layton <jlayton@kernel.org>
References: <20210511214735.1836149-1-willy@infradead.org>
 <20210511214735.1836149-8-willy@infradead.org>
From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <88a265ab-9ecd-18b7-c150-517a5c2e5041@suse.cz>
Date:   Fri, 14 May 2021 13:56:46 +0200
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Nitpick: function names in subject should IMHO also end with (). But not a
reason for resend all patches that don't...

On 5/11/21 11:47 PM, Matthew Wilcox (Oracle) wrote:
> If we know we have a folio, we can call folio_get() instead
> of get_page() and save the overhead of calling compound_head().
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Reviewed-by: Zi Yan <ziy@nvidia.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Acked-by: Jeff Layton <jlayton@kernel.org>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  include/linux/mm.h | 26 +++++++++++++++++---------
>  1 file changed, 17 insertions(+), 9 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 610948f0cb43..feb4645ef4f2 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1219,18 +1219,26 @@ 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) folio_ref_count(folio) + 127u <= 127u)
> +
> +/**
> + * folio_get - Increment the reference count on a folio.
> + * @folio: The folio.
> + *
> + * Context: May be called in any context, as long as you know that
> + * you have a refcount on the folio.  If you do not already have one,
> + * folio_try_get() may be the right interface for you to use.
> + */
> +static inline void folio_get(struct folio *folio)
> +{
> +	VM_BUG_ON_FOLIO(folio_ref_zero_or_close_to_overflow(folio), folio);
> +	folio_ref_inc(folio);
> +}
>  
>  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);
> +	folio_get(page_folio(page));
>  }
>  
>  bool __must_check try_grab_page(struct page *page, unsigned int flags);
>