[v4,04/12] mm: introduce page_ref_sub_return()
diff mbox series

Message ID 20200204234117.2974687-5-jhubbard@nvidia.com
State New
Headers show
Series
  • mm/gup: track FOLL_PIN pages
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Commit Message

John Hubbard Feb. 4, 2020, 11:41 p.m. UTC
An upcoming patch requires subtracting a large chunk of refcounts from
a page, and checking what the resulting refcount is. This is a little
different than the usual "check for zero refcount" that many of the
page ref functions already do. However, it is similar to a few other
routines that (like this one) are generally useful for things such as
1-based refcounting.

Add page_ref_sub_return(), that subtracts a chunk of refcounts
atomically, and returns an atomic snapshot of the result.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 include/linux/page_ref.h | 9 +++++++++
 1 file changed, 9 insertions(+)

Comments

Jan Kara Feb. 5, 2020, 9:23 a.m. UTC | #1
On Tue 04-02-20 15:41:09, John Hubbard wrote:
> An upcoming patch requires subtracting a large chunk of refcounts from
> a page, and checking what the resulting refcount is. This is a little
> different than the usual "check for zero refcount" that many of the
> page ref functions already do. However, it is similar to a few other
> routines that (like this one) are generally useful for things such as
> 1-based refcounting.
> 
> Add page_ref_sub_return(), that subtracts a chunk of refcounts
> atomically, and returns an atomic snapshot of the result.
> 
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  include/linux/page_ref.h | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h
> index 14d14beb1f7f..a0e171265b79 100644
> --- a/include/linux/page_ref.h
> +++ b/include/linux/page_ref.h
> @@ -102,6 +102,15 @@ static inline void page_ref_sub(struct page *page, int nr)
>  		__page_ref_mod(page, -nr);
>  }
>  
> +static inline int page_ref_sub_return(struct page *page, int nr)
> +{
> +	int ret = atomic_sub_return(nr, &page->_refcount);
> +
> +	if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))
> +		__page_ref_mod_and_return(page, -nr, ret);
> +	return ret;
> +}
> +
>  static inline void page_ref_inc(struct page *page)
>  {
>  	atomic_inc(&page->_refcount);
> -- 
> 2.25.0
>
Kirill A. Shutemov Feb. 5, 2020, 11:23 a.m. UTC | #2
On Tue, Feb 04, 2020 at 03:41:09PM -0800, John Hubbard wrote:
> An upcoming patch requires subtracting a large chunk of refcounts from
> a page, and checking what the resulting refcount is. This is a little
> different than the usual "check for zero refcount" that many of the
> page ref functions already do. However, it is similar to a few other
> routines that (like this one) are generally useful for things such as
> 1-based refcounting.
> 
> Add page_ref_sub_return(), that subtracts a chunk of refcounts
> atomically, and returns an atomic snapshot of the result.
> 
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
>  include/linux/page_ref.h | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h
> index 14d14beb1f7f..a0e171265b79 100644
> --- a/include/linux/page_ref.h
> +++ b/include/linux/page_ref.h
> @@ -102,6 +102,15 @@ static inline void page_ref_sub(struct page *page, int nr)
>  		__page_ref_mod(page, -nr);
>  }
>  
> +static inline int page_ref_sub_return(struct page *page, int nr)
> +{
> +	int ret = atomic_sub_return(nr, &page->_refcount);
> +
> +	if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))

s/__tracepoint_page_ref_mod/__tracepoint_page_ref_mod_and_return/

> +		__page_ref_mod_and_return(page, -nr, ret);
> +	return ret;
> +}
> +
>  static inline void page_ref_inc(struct page *page)
>  {
>  	atomic_inc(&page->_refcount);
> -- 
> 2.25.0
>

Patch
diff mbox series

diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h
index 14d14beb1f7f..a0e171265b79 100644
--- a/include/linux/page_ref.h
+++ b/include/linux/page_ref.h
@@ -102,6 +102,15 @@  static inline void page_ref_sub(struct page *page, int nr)
 		__page_ref_mod(page, -nr);
 }
 
+static inline int page_ref_sub_return(struct page *page, int nr)
+{
+	int ret = atomic_sub_return(nr, &page->_refcount);
+
+	if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))
+		__page_ref_mod_and_return(page, -nr, ret);
+	return ret;
+}
+
 static inline void page_ref_inc(struct page *page)
 {
 	atomic_inc(&page->_refcount);