linux-kernel - Re: [PATCH v2 02/28] gup: Remove for_each_compound

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Date:   Mon, 10 Jan 2022 17:11:14 -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 02/28] gup: Remove for_each_compound_head()

On 1/9/22 20:23, Matthew Wilcox (Oracle) wrote:
> This macro doesn't simplify the users; it's easier to just call
> compound_next() inside a standard loop.

Yes it is. :)

> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---

Looks great.

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


thanks,
-- 
John Hubbard
NVIDIA

>   mm/gup.c | 16 +++++-----------
>   1 file changed, 5 insertions(+), 11 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 7a07e0c00bf5..86f8d843de72 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -253,9 +253,6 @@ static inline void compound_next(unsigned long i, unsigned long npages,
>   	struct page *page;
>   	unsigned int nr;
>   
> -	if (i >= npages)
> -		return;
> -
>   	page = compound_head(list[i]);
>   	for (nr = i + 1; nr < npages; nr++) {
>   		if (compound_head(list[nr]) != page)
> @@ -266,12 +263,6 @@ static inline void compound_next(unsigned long i, unsigned long npages,
>   	*ntails = nr - i;
>   }
>   
> -#define for_each_compound_head(__i, __list, __npages, __head, __ntails) \
> -	for (__i = 0, \
> -	     compound_next(__i, __npages, __list, &(__head), &(__ntails)); \
> -	     __i < __npages; __i += __ntails, \
> -	     compound_next(__i, __npages, __list, &(__head), &(__ntails)))
> -
>   /**
>    * unpin_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages
>    * @pages:  array of pages to be maybe marked dirty, and definitely released.
> @@ -306,7 +297,8 @@ void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages,
>   		return;
>   	}
>   
> -	for_each_compound_head(index, pages, npages, head, ntails) {
> +	for (index = 0; index < npages; index += ntails) {
> +		compound_next(index, npages, pages, &head, &ntails);
>   		/*
>   		 * Checking PageDirty at this point may race with
>   		 * clear_page_dirty_for_io(), but that's OK. Two key
> @@ -394,8 +386,10 @@ void unpin_user_pages(struct page **pages, unsigned long npages)
>   	if (WARN_ON(IS_ERR_VALUE(npages)))
>   		return;
>   
> -	for_each_compound_head(index, pages, npages, head, ntails)
> +	for (index = 0; index < npages; index += ntails) {
> +		compound_next(index, npages, pages, &head, &ntails);
>   		put_compound_head(head, ntails, FOLL_PIN);
> +	}
>   }
>   EXPORT_SYMBOL(unpin_user_pages);
>