On 2/3/20 5:23 AM, Kirill A. Shutemov wrote:
On Fri, Jan 31, 2020 at 07:40:21PM -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 | 10 ++++++++++ 1 file changed, 10 insertions(+)
diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h index 14d14beb1f7f..b9cbe553d1e7 100644 --- a/include/linux/page_ref.h +++ b/include/linux/page_ref.h @@ -102,6 +102,16 @@ 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(page, -nr);Shouldn't it be __page_ref_mod_and_return() and relevant tracepoint?
Why yes, it should. I didn't even notice that that more precise function existed, thanks for catching that. I've changed it to this for the next version of the patchset:
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; }
thanks,