Re: [PATCH 08/17] gup: Add try_grab_folio()

[John Hubbard <jhubbard@nvidia.com>]

On 1/2/22 13:57, Matthew Wilcox (Oracle) wrote:
> try_grab_compound_head() is turned into a call to try_grab_folio().
> Convert the two callers who only care about a boolean success/fail.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
>   include/linux/mm.h |  4 +---
>   mm/gup.c           | 25 +++++++++++++------------
>   mm/hugetlb.c       |  7 +++----
>   3 files changed, 17 insertions(+), 19 deletions(-)
> 

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


thanks,
-- 
John Hubbard
NVIDIA

> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 602de23482ef..4e763a590c9c 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1202,9 +1202,7 @@ static inline void get_page(struct page *page)
>   }
>   
>   bool __must_check try_grab_page(struct page *page, unsigned int flags);
> -struct page *try_grab_compound_head(struct page *page, int refs,
> -				    unsigned int flags);
> -
> +struct folio *try_grab_folio(struct page *page, int refs, unsigned int flags);
>   
>   static inline __must_check bool try_get_page(struct page *page)
>   {
> diff --git a/mm/gup.c b/mm/gup.c
> index 6d827f7d66d8..2307b2917055 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -76,12 +76,8 @@ static inline struct folio *try_get_folio(struct page *page, int refs)
>   }
>   
>   /**
> - * try_grab_compound_head() - attempt to elevate a page's refcount, by a
> + * try_grab_folio() - attempt to elevate a page's refcount, by a
>    * flags-dependent amount.
> - *
> - * Even though the name includes "compound_head", this function is still
> - * appropriate for callers that have a non-compound @page to get.
> - *
>    * @page:  pointer to page to be grabbed
>    * @refs:  the value to (effectively) add to the page's refcount
>    * @flags: gup flags: these are the FOLL_* flag values.
> @@ -102,16 +98,15 @@ static inline struct folio *try_get_folio(struct page *page, int refs)
>    *    FOLL_PIN on normal pages, or compound pages that are two pages long:
>    *    page's refcount will be incremented by @refs * GUP_PIN_COUNTING_BIAS.
>    *
> - * Return: head page (with refcount appropriately incremented) for success, or
> + * Return: folio (with refcount appropriately incremented) for success, or
>    * NULL upon failure. If neither FOLL_GET nor FOLL_PIN was set, that's
>    * considered failure, and furthermore, a likely bug in the caller, so a warning
>    * is also emitted.
>    */
> -struct page *try_grab_compound_head(struct page *page,
> -				    int refs, unsigned int flags)
> +struct folio *try_grab_folio(struct page *page, int refs, unsigned int flags)
>   {
>   	if (flags & FOLL_GET)
> -		return &try_get_folio(page, refs)->page;
> +		return try_get_folio(page, refs);
>   	else if (flags & FOLL_PIN) {
>   		struct folio *folio;
>   
> @@ -150,13 +145,19 @@ struct page *try_grab_compound_head(struct page *page,
>   
>   		node_stat_mod_folio(folio, NR_FOLL_PIN_ACQUIRED, refs);
>   
> -		return &folio->page;
> +		return folio;
>   	}
>   
>   	WARN_ON_ONCE(1);
>   	return NULL;
>   }
>   
> +static inline struct page *try_grab_compound_head(struct page *page,
> +		int refs, unsigned int flags)
> +{
> +	return &try_grab_folio(page, refs, flags)->page;
> +}
> +
>   static void gup_put_folio(struct folio *folio, int refs, unsigned int flags)
>   {
>   	if (flags & FOLL_PIN) {
> @@ -188,7 +189,7 @@ static void put_compound_head(struct page *page, int refs, unsigned int flags)
>    * @flags:   gup flags: these are the FOLL_* flag values.
>    *
>    * Either FOLL_PIN or FOLL_GET (or neither) may be set, but not both at the same
> - * time. Cases: please see the try_grab_compound_head() documentation, with
> + * time. Cases: please see the try_grab_folio() documentation, with
>    * "refs=1".
>    *
>    * Return: true for success, or if no action was required (if neither FOLL_PIN
> @@ -200,7 +201,7 @@ bool __must_check try_grab_page(struct page *page, unsigned int flags)
>   	if (!(flags & (FOLL_GET | FOLL_PIN)))
>   		return true;
>   
> -	return try_grab_compound_head(page, 1, flags);
> +	return try_grab_folio(page, 1, flags);
>   }
>   
>   /**
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index abcd1785c629..ab67b13c4a71 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -6072,7 +6072,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
>   
>   		if (pages) {
>   			/*
> -			 * try_grab_compound_head() should always succeed here,
> +			 * try_grab_folio() should always succeed here,
>   			 * because: a) we hold the ptl lock, and b) we've just
>   			 * checked that the huge page is present in the page
>   			 * tables. If the huge page is present, then the tail
> @@ -6081,9 +6081,8 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
>   			 * any way. So this page must be available at this
>   			 * point, unless the page refcount overflowed:
>   			 */
> -			if (WARN_ON_ONCE(!try_grab_compound_head(pages[i],
> -								 refs,
> -								 flags))) {
> +			if (WARN_ON_ONCE(!try_grab_folio(pages[i], refs,
> +							 flags))) {
>   				spin_unlock(ptl);
>   				remainder = 0;
>   				err = -ENOMEM;