mm: unlockless reclaim

unlock_page is fairly expensive.  It can be avoided in page reclaim
success path.  By definition if we have any other references to the page
it would be a bug anyway.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 1 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 412d7872fc75..3b5860294bb6 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -732,7 +732,14 @@ static unsigned long shrink_page_list(struct list_head *page_list,
                 if (!mapping || !__remove_mapping(mapping, page))
                         goto keep_locked;
 
-                unlock_page(page);
+                /*
+                 * At this point, we have no other references and there is
+                 * no way to pick any more up (removed from LRU, removed
+                 * from pagecache). Can use non-atomic bitops now (and
+                 * we obviously don't have to worry about waking up a process
+                 * waiting on the page lock, because there are no references.
+                 */
+                __clear_page_locked(page);
 free_it:
                 nr_reclaimed++;
                 if (!pagevec_add(&freed_pvec, page)) {