Re: [PATCH v4 04/12] mm: introduce page_ref_sub_return()

Jan Kara
2020-02-05T09:23:24Z

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
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR