In put_comound_page(), we call compound_head() after !PageTail
check fails, so in compound_head() PageTail is quite likely to
be true, but instead it is checked with:
if (unlikely(PageTail(page)))
in this case, this unlikely macro is a negative hint for compiler.
So this patch introduce compound_head_by_tail() which deal with
a possible tail page(though it could be spilt by a racy thread),
and make compound_head() a wrapper on it.
Signed-off-by: Jianyu Zhan <nasa4...@gmail.com>
---
include/linux/mm.h | 34 ++++++++++++++++++++++------------
mm/swap.c | 2 +-
2 files changed, 23 insertions(+), 13 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index bf9811e..1bc7baf 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -405,20 +405,30 @@ static inline void compound_unlock_irqrestore(struct page
*page,
#endif
}
+/**
+ * Note: this function must be called on a possible tail page,
+ * this tail page may not be tail anymore upon we calling this funciton,
+ * because we may race with __split_huge_page_refcount tearing down it.
+ */
+static inline struct page *compound_head_by_tail(struct page *page)
+{
+ struct page *head = page->first_page;
+
+ /*
+ * page->first_page may be a dangling pointer to an old
+ * compound page, so recheck that it is still a tail
+ * page before returning.
+ */
+ smp_rmb();
+ if (likely(PageTail(page)))
+ return head;
+ return page;
+}
+
static inline struct page *compound_head(struct page *page)
{
- if (unlikely(PageTail(page))) {
- struct page *head = page->first_page;
-
- /*
- * page->first_page may be a dangling pointer to an old
- * compound page, so recheck that it is still a tail
- * page before returning.
- */
- smp_rmb();
- if (likely(PageTail(page)))
- return head;
- }
+ if (unlikely(PageTail(page)))
+ return compound_head_by_tail(page);
return page;
}
diff --git a/mm/swap.c b/mm/swap.c
index 0d8d891..0b05355 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -256,7 +256,7 @@ static void put_compound_page(struct page *page)
* Case 3 is possible, as we may race with
* __split_huge_page_refcount tearing down a THP page.
*/
- head_page = compound_head(page);
+ head_page = compound_head_by_tail(page);
if (!__compound_tail_refcounted(head_page))
put_unrefcounted_compound_page(head_page, page);
else
--
2.0.0-rc1
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
