linux-kernel - Re: [PATCH v2 01/28] gup: Remove for_each_compound

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Message-ID: <5de5e884-417b-a884-d1b4-55f6892fad8b@nvidia.com>
Date:   Mon, 10 Jan 2022 17:07:12 -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 01/28] gup: Remove for_each_compound_range()

On 1/9/22 20:23, Matthew Wilcox (Oracle) wrote:
> This macro doesn't simplify the users; it's easier to just call
> compound_range_next() inside the loop.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
>   mm/gup.c | 12 ++----------
>   1 file changed, 2 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 2c51e9748a6a..7a07e0c00bf5 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -236,9 +236,6 @@ static inline void compound_range_next(unsigned long i, unsigned long npages,
>   	struct page *next, *page;
>   	unsigned int nr = 1;
>   
> -	if (i >= npages)
> -		return;
> -
>   	next = *list + i;
>   	page = compound_head(next);
>   	if (PageCompound(page) && compound_order(page) >= 1)
> @@ -249,12 +246,6 @@ static inline void compound_range_next(unsigned long i, unsigned long npages,
>   	*ntails = nr;
>   }
>   
> -#define for_each_compound_range(__i, __list, __npages, __head, __ntails) \
> -	for (__i = 0, \
> -	     compound_range_next(__i, __npages, __list, &(__head), &(__ntails)); \
> -	     __i < __npages; __i += __ntails, \
> -	     compound_range_next(__i, __npages, __list, &(__head), &(__ntails)))
> -

Yes!! Thank you.

>   static inline void compound_next(unsigned long i, unsigned long npages,
>   				 struct page **list, struct page **head,
>   				 unsigned int *ntails)
> @@ -371,7 +362,8 @@ void unpin_user_page_range_dirty_lock(struct page *page, unsigned long npages,
>   	struct page *head;
>   	unsigned int ntails;
>   
> -	for_each_compound_range(index, &page, npages, head, ntails) {
> +	for (index = 0; index < npages; index += ntails) {
> +		compound_range_next(index, npages, &page, &head, &ntails);

And now the code is more "honest and up front": items that are changed are
passed by reference, and one can see right here what those are.


>   		if (make_dirty && !PageDirty(head))
>   			set_page_dirty_lock(head);
>   		put_compound_head(head, ntails, FOLL_PIN);

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


thanks,
-- 
John Hubbard
NVIDIA