[patch] mm: unlockless reclaim

[Nick Piggin <npiggin@suse.de>]

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>
---
 mm/vmscan.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

Index: linux-2.6/mm/vmscan.c
===================================================================
--- linux-2.6.orig/mm/vmscan.c
+++ linux-2.6/mm/vmscan.c
@@ -637,7 +637,14 @@ static unsigned long shrink_page_list(st
 		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)) {

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