linux-kernel - Re: [PATCH 2/3] mm/gup: small refactoring: simplify try_grab

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Date:   Mon, 9 Aug 2021 07:38:49 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH 2/3] mm/gup: small refactoring: simplify try_grab_page()

On Sun, Aug 08, 2021 at 04:50:17PM -0700, John Hubbard wrote:
> try_grab_page() does the same thing as try_grab_compound_head(...,
> refs=1, ...), just with a different API. So there is a lot of code
> duplication there.
> 
> Change try_grab_page() to call try_grab_compound_head(), while keeping
> the API contract identical for callers.
> 
> Signed-off-by: John Hubbard <jhubbard@...dia.com>
> ---
>  mm/gup.c | 29 ++---------------------------
>  1 file changed, 2 insertions(+), 27 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 5cb18b62921c..4be6f060fa0b 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -203,33 +203,8 @@ static void put_compound_head(struct page *page, int refs, unsigned int flags)
>   */
>  bool __must_check try_grab_page(struct page *page, unsigned int flags)
>  {
> +	if (flags & (FOLL_GET | FOLL_PIN))
> +		return try_grab_compound_head(page, 1, flags) != NULL;
>  
>  	return true;

Nit: something like:

	if (!(flags & (FOLL_GET | FOLL_PIN)))
		return true;
	return try_grab_compound_head(page, 1, flags) != NULL;

would be a little easier to read.