[PATCH 4/4] dcache: Use rwlock as the underlying lock in rename_lock

[Waiman Long <Waiman.Long@hp.com>]

This patch converts the underlying lock in rename_lock from spinlock
to a read/write lock. This allows multiple blocking readers to proceed
concurrently which is not possible with a spinlock implementation.

As contention of the rename_lock in the d_path() function is a
bottleneck when the perf tool is used to record performance data on
a large SMP system with many cores, converting rename_lock to use
read/write lock will eliminate this bottleneck and the skewing of
perf trace data.

Signed-off-by: Waiman Long <Waiman.Long@hp.com>
---
 fs/dcache.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 480c81f..75299cc 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -82,7 +82,7 @@ int sysctl_vfs_cache_pressure __read_mostly = 100;
 EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);
 
 static __cacheline_aligned_in_smp DEFINE_SPINLOCK(dcache_lru_lock);
-__cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);
+__cacheline_aligned_in_smp DEFINE_SEQRWLOCK(rename_lock);
 
 EXPORT_SYMBOL(rename_lock);
 
-- 
1.7.1