linux-kernel - [PATCH] cleancache: use __read_mostly for cleancache

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Date:	Sun, 29 May 2011 17:38:18 -0300
From:	Cesar Eduardo Barros <cesarb@...arb.net>
To:	linux-mm@...ck.org
Cc:	Minchan Kim <minchan.kim@...il.com>,
	Jan Beulich <JBeulich@...ell.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andreas Dilger <adilger@....com>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	linux-kernel@...r.kernel.org,
	Cesar Eduardo Barros <cesarb@...arb.net>
Subject: [PATCH] cleancache: use __read_mostly for cleancache_enabled

The global variable cleancache_enabled is read often but written to
rarely. Use __read_mostly to prevent it being on the same cacheline as
another variable which is written to often, which would cause cacheline
bouncing.

Signed-off-by: Cesar Eduardo Barros <cesarb@...arb.net>
---
 include/linux/cleancache.h |    2 +-
 mm/cleancache.c            |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/cleancache.h b/include/linux/cleancache.h
index 04ffb2e..83fffe8 100644
--- a/include/linux/cleancache.h
+++ b/include/linux/cleancache.h
@@ -42,7 +42,7 @@ extern void __cleancache_put_page(struct page *);
 extern void __cleancache_flush_page(struct address_space *, struct page *);
 extern void __cleancache_flush_inode(struct address_space *);
 extern void __cleancache_flush_fs(struct super_block *);
-extern int cleancache_enabled;
+extern int cleancache_enabled __read_mostly;
 
 #ifdef CONFIG_CLEANCACHE
 static inline bool cleancache_fs_enabled(struct page *page)
diff --git a/mm/cleancache.c b/mm/cleancache.c
index bcaae4c..a3d7a22 100644
--- a/mm/cleancache.c
+++ b/mm/cleancache.c
@@ -24,7 +24,7 @@
  * disabled), so is preferred to the slower alternative: a function
  * call that checks a non-global.
  */
-int cleancache_enabled;
+int cleancache_enabled __read_mostly;
 EXPORT_SYMBOL(cleancache_enabled);
 
 /*
-- 
1.7.4.4

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