linux-kernel - Re: [PATCH v2 04/28] gup: Optimise compound_range

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Message-ID: <f1b4823c-87c4-993a-eb52-c91219833ebc@nvidia.com>
Date:   Mon, 10 Jan 2022 17:16:55 -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 04/28] gup: Optimise compound_range_next()

On 1/9/22 20:23, Matthew Wilcox (Oracle) wrote:
> By definition, a compound page has an order >= 1, so the second half
> of the test was redundant.  Also, this cannot be a tail page since
> it's the result of calling compound_head(), so use PageHead() instead
> of PageCompound().
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---

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


thanks,
-- 
John Hubbard
NVIDIA

>   mm/gup.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 3c93d2fdf4da..6eedca605b3d 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -237,7 +237,7 @@ static inline struct page *compound_range_next(unsigned long i,
>   
>   	next = start + i;
>   	page = compound_head(next);
> -	if (PageCompound(page) && compound_order(page) >= 1)
> +	if (PageHead(page))
>   		nr = min_t(unsigned int,
>   			   page + compound_nr(page) - next, npages - i);
>