[patch 18/27] fs: dcache reduce dcache_inode_lock

[npiggin@suse.de]

[-- Attachment #1: fs-dcache-d_delete-less-lock.patch --]
[-- Type: text/plain, Size: 1893 bytes --]

dcache_inode_lock can be avoided in d_delete() and d_materialise_unique()
in cases where it is not required.
---
 fs/dcache.c |   23 +++++++++++------------
 1 file changed, 11 insertions(+), 12 deletions(-)

Index: linux-2.6/fs/dcache.c
===================================================================
--- linux-2.6.orig/fs/dcache.c
+++ linux-2.6/fs/dcache.c
@@ -1746,10 +1746,14 @@ void d_delete(struct dentry * dentry)
 	/*
 	 * Are we the only user?
 	 */
-	spin_lock(&dcache_inode_lock);
+again:
 	spin_lock(&dentry->d_lock);
 	isdir = S_ISDIR(dentry->d_inode->i_mode);
 	if (dentry->d_count == 1) {
+		if (!spin_trylock(&dcache_inode_lock)) {
+			spin_unlock(&dentry->d_lock);
+			goto again;
+		}
 		dentry_iput(dentry);
 		fsnotify_nameremove(dentry, isdir);
 		return;
@@ -1759,7 +1763,6 @@ void d_delete(struct dentry * dentry)
 		__d_drop(dentry);
 
 	spin_unlock(&dentry->d_lock);
-	spin_unlock(&dcache_inode_lock);
 
 	fsnotify_nameremove(dentry, isdir);
 }
@@ -2066,14 +2069,15 @@ struct dentry *d_materialise_unique(stru
 
 	BUG_ON(!d_unhashed(dentry));
 
-	spin_lock(&dcache_inode_lock);
-
 	if (!inode) {
 		actual = dentry;
 		__d_instantiate(dentry, NULL);
-		goto found_lock;
+		d_rehash(actual);
+		goto out_nolock;
 	}
 
+	spin_lock(&dcache_inode_lock);
+
 	if (S_ISDIR(inode->i_mode)) {
 		struct dentry *alias;
 
@@ -2101,10 +2105,9 @@ struct dentry *d_materialise_unique(stru
 	actual = __d_instantiate_unique(dentry, inode);
 	if (!actual)
 		actual = dentry;
-	else if (unlikely(!d_unhashed(actual)))
-		goto shouldnt_be_hashed;
+	else
+		BUG_ON(!d_unhashed(actual));
 
-found_lock:
 	spin_lock(&actual->d_lock);
 found:
 	_d_rehash(actual);
@@ -2118,10 +2121,6 @@ out_nolock:
 
 	iput(inode);
 	return actual;
-
-shouldnt_be_hashed:
-	spin_unlock(&dcache_inode_lock);
-	BUG();
 }
 
 static int prepend(char **buffer, int *buflen, const char *str, int namelen)