mm/page-writeback: introduce tracepoint for wait_on_page_writeback()

Recently there have been some hung tasks on our server due to
wait_on_page_writeback(), and we want to know the details of this
PG_writeback, i.e.  this page is writing back to which device.  But it is
not so convenient to get the details.

I think it would be better to introduce a tracepoint for diagnosing the
writeback details.

Link: http://lkml.kernel.org/r/1556274402-19018-1-git-send-email-laoar.shao@gmail.com
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 9 deletions

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 2e8438a1216a..112f15bb5907 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -540,15 +540,7 @@ static inline int wait_on_page_locked_killable(struct page *page)
 
 extern void put_and_wait_on_page_locked(struct page *page);
 
-/* 
- * Wait for a page to complete writeback
- */
-static inline void wait_on_page_writeback(struct page *page)
-{
-	if (PageWriteback(page))
-		wait_on_page_bit(page, PG_writeback);
-}
-
+void wait_on_page_writeback(struct page *page);
 extern void end_page_writeback(struct page *page);
 void wait_for_stable_page(struct page *page);