[PATCH] remove dparent_lock

The big SMP machines are seeing quite some contention in dnotify_parent()
(via vfs_write).  This function is hammering the global dparent_lock.

However we don't actually need a global dparent_lock for pinning down
dentry->d_parent.  We can use dentry->d_lock for this.  That is already being
held across d_move.

This patch speeds up SDET on the 16-way by 5% and wipes dnotify_parent() off
the profiles.

It also uninlines dnofity_parent().

It also uses spin_lock(), which is faster than read_lock().

I'm not sure that we need to take both the source and target dentry's d_lock
in d_move.

The patch also does lots of s/__inline__/inline/ in dcache.h

Documentation/filesystems/porting

@@ -208,10 +208,10 @@ had ->revalidate()) add calls in ->follow_link()/->readlink().
 if at least one of the following is true:
 	* filesystem has no cross-directory rename()
 	* dcache_lock is held
-	* dparent_lock is held (shared)
 	* we know that parent had been locked (e.g. we are looking at
 ->d_parent of ->lookup() argument).
 	* we are called from ->rename().
+	* the child's ->d_lock is held
 Audit your code and add locking if needed.  Notice that any place that is
 not protected by the conditions above is risky even in the old tree - you
 had been relying on BKL and that's prone to screwups.  Old tree had quite

fs/afs/dir.c

@@ -497,11 +497,7 @@ static int afs_d_revalidate(struct dentry *dentry, int flags)
 
 	_enter("%s,%x",dentry->d_name.name,flags);
 
-	/* lock down the parent dentry so we can peer at it */
-	read_lock(&dparent_lock);
-	parent = dget(dentry->d_parent);
-	read_unlock(&dparent_lock);
-
+	parent = dget_parent(dentry);
 	dir = parent->d_inode;
 	inode = dentry->d_inode;
 

fs/dcache.c

@@ -33,7 +33,6 @@
 /* #define DCACHE_DEBUG 1 */
 
 spinlock_t dcache_lock __cacheline_aligned_in_smp = SPIN_LOCK_UNLOCKED;
-rwlock_t dparent_lock __cacheline_aligned_in_smp = RW_LOCK_UNLOCKED;
 seqlock_t rename_lock __cacheline_aligned_in_smp = SEQLOCK_UNLOCKED;
 
 static kmem_cache_t *dentry_cache; 
@@ -1205,7 +1204,16 @@ void d_move(struct dentry * dentry, struct dentry * target)
 
 	spin_lock(&dcache_lock);
 	write_seqlock(&rename_lock);
-	spin_lock(&dentry->d_lock);
+	/*
+	 * XXXX: do we really need to take target->d_lock?
+	 */
+	if (target < dentry) {
+		spin_lock(&target->d_lock);
+		spin_lock(&dentry->d_lock);
+	} else {
+		spin_lock(&dentry->d_lock);
+		spin_lock(&target->d_lock);
+	}
 
 	/* Move the dentry to the target hash queue, if on different bucket */
 	if (dentry->d_bucket != target->d_bucket) {
@@ -1225,8 +1233,8 @@ void d_move(struct dentry * dentry, struct dentry * target)
 	smp_wmb();
 	do_switch(dentry->d_name.len, target->d_name.len);
 	do_switch(dentry->d_name.hash, target->d_name.hash);
+
 	/* ... and switch the parents */
-	write_lock(&dparent_lock);
 	if (IS_ROOT(dentry)) {
 		dentry->d_parent = target->d_parent;
 		target->d_parent = target;
@@ -1237,10 +1245,10 @@ void d_move(struct dentry * dentry, struct dentry * target)
 		/* And add them back to the (new) parent lists */
 		list_add(&target->d_child, &target->d_parent->d_subdirs);
 	}
-	write_unlock(&dparent_lock);
 
 	list_add(&dentry->d_child, &dentry->d_parent->d_subdirs);
 	dentry->d_move_count++;
+	spin_unlock(&target->d_lock);
 	spin_unlock(&dentry->d_lock);
 	write_sequnlock(&rename_lock);
 	spin_unlock(&dcache_lock);

fs/dnotify.c

@@ -142,6 +142,29 @@ void __inode_dir_notify(struct inode *inode, unsigned long event)
 	write_unlock(&dn_lock);
 }
 
+/*
+ * This is hopelessly wrong, but unfixable without API changes.  At
+ * least it doesn't oops the kernel...
+ *
+ * To safely access ->d_parent we need to keep d_move away from it.  Use the
+ * dentry's d_lock for this.
+ */
+void dnotify_parent(struct dentry *dentry, unsigned long event)
+{
+	struct dentry *parent;
+
+	spin_lock(&dentry->d_lock);
+	parent = dentry->d_parent;
+	if (parent->d_inode->i_dnotify_mask & event) {
+		dget(parent);
+		spin_unlock(&dentry->d_lock);
+		__inode_dir_notify(parent->d_inode, event);
+		dput(parent);
+	} else {
+		spin_unlock(&dentry->d_lock);
+	}
+}
+
 static int __init dnotify_init(void)
 {
 	dn_cache = kmem_cache_create("dnotify_cache",

fs/exportfs/expfs.c

@@ -140,13 +140,20 @@ find_exported_dentry(struct super_block *sb, void *obj, void *parent,
 	noprogress= 0;
 	while (target_dir->d_flags & DCACHE_DISCONNECTED && noprogress++ < 10) {
 		struct dentry *pd = target_dir;
-		read_lock(&dparent_lock);
-		while (!IS_ROOT(pd) &&
-		       (pd->d_parent->d_flags & DCACHE_DISCONNECTED))
-			pd = pd->d_parent;
 
 		dget(pd);
-		read_unlock(&dparent_lock);
+		spin_lock(&pd->d_lock);
+		while (!IS_ROOT(pd) &&
+				(pd->d_parent->d_flags&DCACHE_DISCONNECTED)) {
+			struct dentry *parent = pd->d_parent;
+
+			dget(parent);
+			spin_unlock(&pd->d_lock);
+			dput(pd);
+			pd = parent;
+			spin_lock(&pd->d_lock);
+		}
+		spin_unlock(&pd->d_lock);
 
 		if (!IS_ROOT(pd)) {
 			/* must have found a connected parent - great */
@@ -469,11 +476,12 @@ static int export_encode_fh(struct dentry *dentry, __u32 *fh, int *max_len,
 	fh[1] = inode->i_generation;
 	if (connectable && !S_ISDIR(inode->i_mode)) {
 		struct inode *parent;
-		read_lock(&dparent_lock);
+
+		spin_lock(&dentry->d_lock);
 		parent = dentry->d_parent->d_inode;
 		fh[2] = parent->i_ino;
 		fh[3] = parent->i_generation;
-		read_unlock(&dparent_lock);
+		spin_unlock(&dentry->d_lock);
 		len = 4;
 		type = 2;
 	}

fs/fat/inode.c

@@ -624,9 +624,9 @@ int fat_encode_fh(struct dentry *de, __u32 *fh, int *lenp, int connectable)
 	fh[1] = inode->i_generation;
 	fh[2] = MSDOS_I(inode)->i_location;
 	fh[3] = MSDOS_I(inode)->i_logstart;
-	read_lock(&dparent_lock);
+	spin_lock(&de->d_lock);
 	fh[4] = MSDOS_I(de->d_parent->d_inode)->i_logstart;
-	read_unlock(&dparent_lock);
+	spin_unlock(&de->d_lock);
 	return 3;
 }
 

fs/ncpfs/dir.c

@@ -273,9 +273,7 @@ __ncp_lookup_validate(struct dentry * dentry, int flags)
 	int res, val = 0, len = dentry->d_name.len + 1;
 	__u8 __name[len];
 
-	read_lock(&dparent_lock);
-	parent = dget(dentry->d_parent);
-	read_unlock(&dparent_lock);
+	parent = dget_parent(dentry);
 	dir = parent->d_inode;
 
 	if (!dentry->d_inode)

fs/nfs/dir.c

@@ -503,9 +503,7 @@ static int nfs_lookup_revalidate(struct dentry * dentry, int flags)
 	struct nfs_fh fhandle;
 	struct nfs_fattr fattr;
 
-	read_lock(&dparent_lock);
-	parent = dget(dentry->d_parent);
-	read_unlock(&dparent_lock);
+	parent = dget_parent(dentry);
 	lock_kernel();
 	dir = parent->d_inode;
 	inode = dentry->d_inode;

fs/nfsd/export.c

@@ -545,9 +545,8 @@ exp_parent(svc_client *clp, struct vfsmount *mnt, struct dentry *dentry,
 
 	while (exp == NULL && !IS_ROOT(dentry)) {
 		struct dentry *parent;
-		read_lock(&dparent_lock);
-		parent = dget(dentry->d_parent);
-		read_unlock(&dparent_lock);
+
+		parent = dget_parent(dentry);
 		dput(dentry);
 		dentry = parent;
 		exp = exp_get_by_name(clp, mnt, dentry, reqp);

fs/nfsd/nfs3xdr.c

@@ -820,9 +820,7 @@ encode_entry(struct readdir_cd *ccd, const char *name,
 		fh_init(&fh, NFS3_FHSIZE);
 		if (isdotent(name, namlen)) {
 			if (namlen == 2) {
-				read_lock(&dparent_lock);
-				dchild = dget(dparent->d_parent);
-				read_unlock(&dparent_lock);
+				dchild = dget_parent(dparent);
 			} else
 				dchild = dget(dparent);
 		} else

fs/nfsd/nfsfh.c

@@ -55,9 +55,7 @@ int nfsd_acceptable(void *expv, struct dentry *dentry)
 	while (tdentry != exp->ex_dentry && ! IS_ROOT(tdentry)) {
 		/* make sure parents give x permission to user */
 		int err;
-		read_lock(&dparent_lock);
-		parent = dget(tdentry->d_parent);
-		read_unlock(&dparent_lock);
+		parent = dget_parent(tdentry);
 		err = permission(parent->d_inode, S_IXOTH);
 		if (err < 0) {
 			dput(parent);

fs/nfsd/vfs.c

@@ -112,9 +112,7 @@ nfsd_lookup(struct svc_rqst *rqstp, struct svc_fh *fhp, const char *name,
 		if (len==1)
 			dentry = dget(dparent);
 		else if (dparent != exp->ex_dentry) {
-			read_lock(&dparent_lock);
-			dentry = dget(dparent->d_parent);
-			read_unlock(&dparent_lock);
+			dentry = dget_parent(dparent);
 		} else  if (!EX_NOHIDE(exp))
 			dentry = dget(dparent); /* .. == . just like at / */
 		else {
@@ -125,9 +123,7 @@ nfsd_lookup(struct svc_rqst *rqstp, struct svc_fh *fhp, const char *name,
 			dentry = dget(dparent);
 			while(follow_up(&mnt, &dentry))
 				;
-			read_lock(&dparent_lock);
-			dp = dget(dentry->d_parent);
-			read_unlock(&dparent_lock);
+			dp = dget_parent(dentry);
 			dput(dentry);
 			dentry = dp;
 

fs/ntfs/namei.c

@@ -241,7 +241,8 @@ static struct dentry *ntfs_lookup(struct inode *dir_ino, struct dentry *dent)
 	nls_name.hash = full_name_hash(nls_name.name, nls_name.len);
 
 	/*
-	 * Note: No need for dparent_lock as i_sem is held on the parent inode.
+	 * Note: No need for dent->d_lock lock as i_sem is held on the
+	 * parent inode.
 	 */
 
 	/* Does a dentry matching the nls_name exist already? */

fs/reiserfs/inode.c

@@ -1321,7 +1321,7 @@ int reiserfs_encode_fh(struct dentry *dentry, __u32 *data, int *lenp, int need_p
     if (maxlen < 5 || ! need_parent)
         return 3 ;
 
-    read_lock(&dparent_lock);
+    spin_lock(&dentry->d_lock);
     inode = dentry->d_parent->d_inode ;
     data[3] = inode->i_ino ;
     data[4] = le32_to_cpu(INODE_PKEY (inode)->k_dir_id) ;
@@ -1330,7 +1330,7 @@ int reiserfs_encode_fh(struct dentry *dentry, __u32 *data, int *lenp, int need_p
 	    data[5] = inode->i_generation ;
 	    *lenp = 6 ;
     }
-    read_unlock(&dparent_lock);
+    spin_unlock(&dentry->d_lock);
     return *lenp ;
 }
 

fs/smbfs/dir.c

@@ -400,14 +400,23 @@ smb_new_dentry(struct dentry *dentry)
 void
 smb_renew_times(struct dentry * dentry)
 {
-	read_lock(&dparent_lock);
+	dget(dentry);
+	spin_lock(&dentry->d_lock);
 	for (;;) {
+		struct dentry *parent;
+
 		dentry->d_time = jiffies;
 		if (IS_ROOT(dentry))
 			break;
-		dentry = dentry->d_parent;
+		parent = dentry->d_parent;
+		dget(parent);
+		spin_unlock(&dentry->d_lock);
+		dput(dentry);
+		dentry = parent;
+		spin_lock(&dentry->d_lock);
 	}
-	read_unlock(&dparent_lock);
+	spin_unlock(&dentry->d_lock);
+	dput(dentry);
 }
 
 static struct dentry *

fs/smbfs/proc.c

@@ -333,10 +333,14 @@ static int smb_build_path(struct smb_sb_info *server, unsigned char *buf,
 	 * Build the path string walking the tree backward from end to ROOT
 	 * and store it in reversed order [see reverse_string()]
 	 */
-	read_lock(&dparent_lock);
+	dget(entry);
+	spin_lock(&entry->d_lock);
 	while (!IS_ROOT(entry)) {
+		struct dentry *parent;
+
 		if (maxlen < (3<<unicode)) {
-			read_unlock(&dparent_lock);
+			spin_unlock(&entry->d_lock);
+			dput(entry);
 			return -ENAMETOOLONG;
 		}
 
@@ -344,7 +348,8 @@ static int smb_build_path(struct smb_sb_info *server, unsigned char *buf,
 				      entry->d_name.name, entry->d_name.len,
 				      server->local_nls, server->remote_nls);
 		if (len < 0) {
-			read_unlock(&dparent_lock);
+			spin_unlock(&entry->d_lock);
+			dput(entry);
 			return len;
 		}
 		reverse_string(path, len);
@@ -357,9 +362,15 @@ static int smb_build_path(struct smb_sb_info *server, unsigned char *buf,
 		*path++ = '\\';
 		maxlen -= len+1;
 
-		entry = entry->d_parent;
+		parent = entry->d_parent;
+		dget(parent);
+		spin_unlock(&entry->d_lock);
+		dput(entry);
+		entry = parent;
+		spin_lock(&entry->d_lock);
 	}
-	read_unlock(&dparent_lock);
+	spin_unlock(&entry->d_lock);
+	dput(entry);
 	reverse_string(buf, path-buf);
 
 	/* maxlen has space for at least one char */

include/linux/dcache.h

@@ -48,19 +48,24 @@ extern struct dentry_stat_t dentry_stat;
 #define init_name_hash()		0
 
 /* partial hash update function. Assume roughly 4 bits per character */
-static __inline__ unsigned long partial_name_hash(unsigned long c, unsigned long prevhash)
+static inline unsigned long
+partial_name_hash(unsigned long c, unsigned long prevhash)
 {
 	return (prevhash + (c << 4) + (c >> 4)) * 11;
 }
 
-/* Finally: cut down the number of bits to a int value (and try to avoid losing bits) */
-static __inline__ unsigned long end_name_hash(unsigned long hash)
+/*
+ * Finally: cut down the number of bits to a int value (and try to avoid
+ * losing bits)
+ */
+static inline unsigned long end_name_hash(unsigned long hash)
 {
 	return (unsigned int) hash;
 }
 
 /* Compute the hash for a name string. */
-static __inline__ unsigned int full_name_hash(const unsigned char * name, unsigned int len)
+static inline unsigned int
+full_name_hash(const unsigned char *name, unsigned int len)
 {
 	unsigned long hash = init_name_hash();
 	while (len--)
@@ -149,7 +154,6 @@ d_iput:		no		no		yes
 #define DCACHE_UNHASHED		0x0010	
 
 extern spinlock_t dcache_lock;
-extern rwlock_t dparent_lock;
 
 /**
  * d_drop - drop a dentry
@@ -168,20 +172,20 @@ extern rwlock_t dparent_lock;
  * timeouts or autofs deletes).
  */
 
-static __inline__ void __d_drop(struct dentry * dentry)
+static inline void __d_drop(struct dentry *dentry)
 {
 	dentry->d_vfs_flags |= DCACHE_UNHASHED;
 	hlist_del_rcu(&dentry->d_hash);
 }
 
-static __inline__ void d_drop(struct dentry * dentry)
+static inline void d_drop(struct dentry *dentry)
 {
 	spin_lock(&dcache_lock);
  	__d_drop(dentry);
 	spin_unlock(&dcache_lock);
 }
 
-static __inline__ int dname_external(struct dentry *d)
+static inline int dname_external(struct dentry *d)
 {
 	return d->d_name.name != d->d_iname; 
 }
@@ -227,7 +231,7 @@ extern void d_rehash(struct dentry *);
  * The entry was actually filled in earlier during d_alloc().
  */
  
-static __inline__ void d_add(struct dentry * entry, struct inode * inode)
+static inline void d_add(struct dentry *entry, struct inode *inode)
 {
 	d_instantiate(entry, inode);
 	d_rehash(entry);
@@ -260,7 +264,7 @@ extern char * d_path(struct dentry *, struct vfsmount *, char *, int);
  *	and call dget_locked() instead of dget().
  */
  
-static __inline__ struct dentry * dget(struct dentry *dentry)
+static inline struct dentry *dget(struct dentry *dentry)
 {
 	if (dentry) {
 		if (!atomic_read(&dentry->d_count))
@@ -280,14 +284,24 @@ extern struct dentry * dget_locked(struct dentry *);
  *	Returns true if the dentry passed is not currently hashed.
  */
  
-static __inline__ int d_unhashed(struct dentry *dentry)
+static inline int d_unhashed(struct dentry *dentry)
 {
 	return (dentry->d_vfs_flags & DCACHE_UNHASHED);
 }
 
+static inline struct dentry *dget_parent(struct dentry *dentry)
+{
+	struct dentry *ret;
+
+	spin_lock(&dentry->d_lock);
+	ret = dget(dentry->d_parent);
+	spin_unlock(&dentry->d_lock);
+	return ret;
+}
+
 extern void dput(struct dentry *);
 
-static __inline__ int d_mountpoint(struct dentry *dentry)
+static inline int d_mountpoint(struct dentry *dentry)
 {
 	return dentry->d_mounted;
 }

include/linux/dnotify.h

@@ -18,27 +18,10 @@ struct dnotify_struct {
 extern void __inode_dir_notify(struct inode *, unsigned long);
 extern void dnotify_flush(struct file *filp, fl_owner_t id);
 extern int fcntl_dirnotify(int, struct file *, unsigned long);
+void dnotify_parent(struct dentry *dentry, unsigned long event);
 
 static inline void inode_dir_notify(struct inode *inode, unsigned long event)
 {
 	if ((inode)->i_dnotify_mask & (event))
 		__inode_dir_notify(inode, event);
 }
-
-/*
- * This is hopelessly wrong, but unfixable without API changes.  At
- * least it doesn't oops the kernel...
- */
-static inline void dnotify_parent(struct dentry *dentry, unsigned long event)
-{
-	struct dentry *parent;
-	read_lock(&dparent_lock);
-	parent = dentry->d_parent;
-	if (parent->d_inode->i_dnotify_mask & event) {
-		dget(parent);
-		read_unlock(&dparent_lock);
-		__inode_dir_notify(parent->d_inode, event);
-		dput(parent);
-	} else
-		read_unlock(&dparent_lock);
-}

include/linux/fs.h

@@ -1306,9 +1306,10 @@ extern void inode_update_time(struct inode *inode, int ctime_too);
 static inline ino_t parent_ino(struct dentry *dentry)
 {
 	ino_t res;
-	read_lock(&dparent_lock);
+
+	spin_lock(&dentry->d_lock);
 	res = dentry->d_parent->d_inode->i_ino;
-	read_unlock(&dparent_lock);
+	spin_unlock(&dentry->d_lock);
 	return res;
 }
 

kernel/ksyms.c

@@ -159,7 +159,6 @@ EXPORT_SYMBOL(lookup_one_len);
 EXPORT_SYMBOL(lookup_hash);
 EXPORT_SYMBOL(sys_close);
 EXPORT_SYMBOL(dcache_lock);
-EXPORT_SYMBOL(dparent_lock);
 EXPORT_SYMBOL(d_alloc_root);
 EXPORT_SYMBOL(d_delete);
 EXPORT_SYMBOL(dget_locked);