linux-kernel - [PATCH] fs: super: do not cacheline align s_{inode,dentry}

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Date:	Mon, 19 Jan 2015 15:29:23 +0300
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Alexander Viro <viro@...iv.linux.org.uk>
CC:	<linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] fs: super: do not cacheline align s_{inode,dentry}_lru

super_block->s_{inode,dentry}_lru were made cacheline aligned, because
the list_lru struct had a spinlock and a list embedded to it and
therefore could be actively modified.

Today, struct list_lru is, in fact, read-only: the lists and locks live
in list_lru_node's, which list_lru points to. The list_lru_node struct
is already cacheline aligned by definition.

So let us drop the cacheline aligned annotation in order not to waste
space in struct super_block.

Signed-off-by: Vladimir Davydov <vdavydov@...allels.com>
---
 include/linux/fs.h |    9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 0bd9669ce91d..790e534adbc7 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1309,12 +1309,9 @@ struct super_block {
 	struct workqueue_struct *s_dio_done_wq;
 	struct hlist_head s_pins;
 
-	/*
-	 * Keep the lru lists last in the structure so they always sit on their
-	 * own individual cachelines.
-	 */
-	struct list_lru		s_dentry_lru ____cacheline_aligned_in_smp;
-	struct list_lru		s_inode_lru ____cacheline_aligned_in_smp;
+	struct list_lru		s_dentry_lru;
+	struct list_lru		s_inode_lru;
+
 	struct rcu_head		rcu;
 
 	/*
-- 
1.7.10.4

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