linux-kernel - [PATCH] fs-writeback : check sync bit earlier in inode_wait_for

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Date:	Fri, 16 Apr 2010 16:33:39 +0100
From:	Richard Kennedy <richard@....demon.co.uk>
To:	Alexander Viro <viro@...iv.linux.org.uk>,
	Jens Axboe <jens.axboe@...cle.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Wu Fengguang <fengguang.wu@...el.com>
Subject: [PATCH] fs-writeback : check sync bit earlier in
 inode_wait_for_writeback

When wb_writeback() hasn't written anything it will re-acquire the inode
lock before calling inode_wait_for_writeback. 

This change tests the sync bit first so that is doesn't need to drop &
re-acquire the lock if the inode became available while wb_writeback()
was waiting to get the lock.

Signed-off-by: Richard Kennedy <richard@....demon.co.uk>

----
patch against 2.6.34-rc4
compiled & tested on 86_64

regards
Richard


diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 4b37f7c..b1e398e 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -398,11 +398,11 @@ static void inode_wait_for_writeback(struct inode *inode)
 	wait_queue_head_t *wqh;
 
 	wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
-	do {
+	 while (inode->i_state & I_SYNC) {
 		spin_unlock(&inode_lock);
 		__wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE);
 		spin_lock(&inode_lock);
-	} while (inode->i_state & I_SYNC);
+	}
 }
 
 /*


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