From 89e6054836a7b1e7500cd70a14b5579e752c9250 Mon Sep 17 00:00:00 2001
From: Nick Piggin <npiggin@kernel.dk>
Date: Fri, 7 Jan 2011 17:49:45 +1100
Subject: [PATCH] fs: dcache reduce prune_one_dentry locking
prune_one_dentry can avoid quite a bit of locking in the common case where
ancestors have an elevated refcount. Alternatively, we could have gone the
other way and made fewer trylocks in the case where d_count goes to zero, but
is probably less common.
Signed-off-by: Nick Piggin <npiggin@kernel.dk>
---
fs/dcache.c | 27 +++++++++++++++------------
1 file changed, 15 insertions(+), 12 deletions(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index a8f89765d602..195706374697 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -582,26 +582,29 @@ static void prune_one_dentry(struct dentry *dentry, struct dentry *parent)
* Prune ancestors.
*/
while (dentry) {
- spin_lock(&dcache_inode_lock);
-again:
+relock:
spin_lock(&dentry->d_lock);
+ if (dentry->d_count > 1) {
+ dentry->d_count--;
+ spin_unlock(&dentry->d_lock);
+ return;
+ }
+ if (!spin_trylock(&dcache_inode_lock)) {
+relock2:
+ spin_unlock(&dentry->d_lock);
+ cpu_relax();
+ goto relock;
+ }
+
if (IS_ROOT(dentry))
parent = NULL;
else
parent = dentry->d_parent;
if (parent && !spin_trylock(&parent->d_lock)) {
- spin_unlock(&dentry->d_lock);
- goto again;
+ spin_unlock(&dcache_inode_lock);
+ goto relock2;
}
dentry->d_count--;
- if (dentry->d_count) {
- if (parent)
- spin_unlock(&parent->d_lock);
- spin_unlock(&dentry->d_lock);
- spin_unlock(&dcache_inode_lock);
- return;
- }
-
dentry_lru_del(dentry);
__d_drop(dentry);
dentry = d_kill(dentry, parent);