linux-kernel - [PATCH] fs/aio.c: eliminate redundant loads in put_aio_ring

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Date:   Thu, 15 Sep 2016 00:25:03 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Benjamin LaHaise <bcrl@...ck.org>,
        Alexander Viro <viro@...iv.linux.org.uk>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-fsdevel@...r.kernel.org, linux-aio@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] fs/aio.c: eliminate redundant loads in put_aio_ring_file

Using a local variable we can prevent gcc from reloading
aio_ring_file->f_inode->i_mapping twice, eliminating 2x2 dependent
loads.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 fs/aio.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index fb8e45b88cd4..32ce10e55723 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -269,14 +269,17 @@ __initcall(aio_setup);
 static void put_aio_ring_file(struct kioctx *ctx)
 {
 	struct file *aio_ring_file = ctx->aio_ring_file;
+	struct address_space *i_mapping;
+
 	if (aio_ring_file) {
 		truncate_setsize(aio_ring_file->f_inode, 0);
 
 		/* Prevent further access to the kioctx from migratepages */
-		spin_lock(&aio_ring_file->f_inode->i_mapping->private_lock);
-		aio_ring_file->f_inode->i_mapping->private_data = NULL;
+		i_mapping = aio_ring_file->f_inode->i_mapping;
+		spin_lock(&i_mapping->private_lock);
+		i_mapping->private_data = NULL;
 		ctx->aio_ring_file = NULL;
-		spin_unlock(&aio_ring_file->f_inode->i_mapping->private_lock);
+		spin_unlock(&i_mapping->private_lock);
 
 		fput(aio_ring_file);
 	}
-- 
2.1.4