commit 451ea25da71590361c71bf3044c55b870a887d53
author Johannes Weiner <hannes@cmpxchg.org> Mon Sep 21 17:01:48 2009 -0700
committer Linus Torvalds <torvalds@linux-foundation.org> Tue Sep 22 07:17:30 2009 -0700
tree e2e9de6e7c1fb4f79c0413a3c4d401ec9263b722
parent bf88c8c83e4425d17e29daa5354ffb1f8ba7b225

mm: perform non-atomic test-clear of PG_mlocked on free

By the time PG_mlocked is cleared in the page freeing path, nobody else is
looking at our page->flags anymore.

It is thus safe to make the test-and-clear non-atomic and thereby removing
an unnecessary and expensive operation from a hotpath.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Christoph Lameter <cl@linux-foundation.org>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/page-flags.h

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 2b87acf..d07c0bb 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -158,6 +158,9 @@
 static inline int TestClearPage##uname(struct page *page)		\
 		{ return test_and_clear_bit(PG_##lname, &page->flags); }
 
+#define __TESTCLEARFLAG(uname, lname)					\
+static inline int __TestClearPage##uname(struct page *page)		\
+		{ return __test_and_clear_bit(PG_##lname, &page->flags); }
 
 #define PAGEFLAG(uname, lname) TESTPAGEFLAG(uname, lname)		\
 	SETPAGEFLAG(uname, lname) CLEARPAGEFLAG(uname, lname)
@@ -184,6 +187,9 @@
 #define TESTCLEARFLAG_FALSE(uname)					\
 static inline int TestClearPage##uname(struct page *page) { return 0; }
 
+#define __TESTCLEARFLAG_FALSE(uname)					\
+static inline int __TestClearPage##uname(struct page *page) { return 0; }
+
 struct page;	/* forward declaration */
 
 TESTPAGEFLAG(Locked, locked) TESTSETFLAG(Locked, locked)
@@ -250,11 +256,11 @@
 #ifdef CONFIG_HAVE_MLOCKED_PAGE_BIT
 #define MLOCK_PAGES 1
 PAGEFLAG(Mlocked, mlocked) __CLEARPAGEFLAG(Mlocked, mlocked)
-	TESTSCFLAG(Mlocked, mlocked)
+	TESTSCFLAG(Mlocked, mlocked) __TESTCLEARFLAG(Mlocked, mlocked)
 #else
 #define MLOCK_PAGES 0
-PAGEFLAG_FALSE(Mlocked)
-	SETPAGEFLAG_NOOP(Mlocked) TESTCLEARFLAG_FALSE(Mlocked)
+PAGEFLAG_FALSE(Mlocked) SETPAGEFLAG_NOOP(Mlocked)
+	TESTCLEARFLAG_FALSE(Mlocked) __TESTCLEARFLAG_FALSE(Mlocked)
 #endif
 
 #ifdef CONFIG_ARCH_USES_PG_UNCACHED

mm/page_alloc.c

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 81926c7..9242d13 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -557,7 +557,7 @@
 	unsigned long flags;
 	int i;
 	int bad = 0;
-	int wasMlocked = TestClearPageMlocked(page);
+	int wasMlocked = __TestClearPageMlocked(page);
 
 	kmemcheck_free_shadow(page, order);
 
@@ -1026,7 +1026,7 @@
 	struct zone *zone = page_zone(page);
 	struct per_cpu_pages *pcp;
 	unsigned long flags;
-	int wasMlocked = TestClearPageMlocked(page);
+	int wasMlocked = __TestClearPageMlocked(page);
 
 	kmemcheck_free_shadow(page, 0);