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.
Reviewed-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
---
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..d27701199a4d 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_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
