linux-kernel - [patch] mm: unlockless reclaim

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Date:	Sun, 11 Nov 2007 09:40:12 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: [patch] mm: unlockless reclaim

Combined with the previous and subsequent patches, throughput of pages through
the pagecache on an Opteron system here goes up by anywhere from 50% to 500%,
depending on the number of files and threads involved.
--

unlock_page is fairly expensive. It can be avoided in page reclaim.

Signed-off-by: Nick Piggin <npiggin@...e.de>
---
Index: linux-2.6/mm/vmscan.c
===================================================================
--- linux-2.6.orig/mm/vmscan.c
+++ linux-2.6/mm/vmscan.c
@@ -589,7 +589,14 @@ static unsigned long shrink_page_list(st
 			goto keep_locked;
 
 free_it:
-		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);
 		nr_reclaimed++;
 		if (!pagevec_add(&freed_pvec, page))
 			__pagevec_release_nonlru(&freed_pvec);
-
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