linux-kernel - [PATCH 2/7] kill-the-bkl/reiserfs: conditionaly release the write lock on fs

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Date:	Fri,  8 May 2009 20:35:19 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jeff Mahoney <jeffm@...e.com>,
	Chris Mason <chris.mason@...cle.com>,
	Ingo Molnar <mingo@...e.hu>,
	Alexander Beregalov <a.beregalov@...il.com>
Subject: [PATCH 2/7] kill-the-bkl/reiserfs: conditionaly release the write lock on fs_changed()

The goal of fs_changed() is to check whether the tree changed during a
schedule(). This is a BKL legacy.

A recent patch added an explicit unconditional release/reacquire of the
write lock around the cond_resched() called inside fs_changed.

But it's wasteful to unconditionally do that, we are creating superfluous
lock contention in !TIF_NEED_RESCHED case.

This patch manage that by calling reiserfs_cond_resched() from fs_changed()
which only releases the lock if we are going to reschedule.

[ Impact: inject less lock contention and tree job retries ]

Cc: Jeff Mahoney <jeffm@...e.com>
Cc: Chris Mason <chris.mason@...cle.com>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Alexander Beregalov <a.beregalov@...il.com>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
---
 include/linux/reiserfs_fs.h |    4 +---
 1 files changed, 1 insertions(+), 3 deletions(-)

diff --git a/include/linux/reiserfs_fs.h b/include/linux/reiserfs_fs.h
index 995bdf9..39bd4ea 100644
--- a/include/linux/reiserfs_fs.h
+++ b/include/linux/reiserfs_fs.h
@@ -1317,9 +1317,7 @@ static inline loff_t max_reiserfs_offset(struct inode *inode)
 #define __fs_changed(gen,s) (gen != get_generation (s))
 #define fs_changed(gen,s)		\
 ({					\
-	reiserfs_write_unlock(s);	\
-	cond_resched();			\
-	reiserfs_write_lock(s);		\
+	reiserfs_cond_resched(s);	\
 	__fs_changed(gen, s);		\
 })
 
-- 
1.6.2.3

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