fs: dcache scale dentry refcount

Make d_count non-atomic and protect it with d_lock. This allows us to ensure a
0 refcount dentry remains 0 without dcache_lock. It is also fairly natural when
we start protecting many other dentry members with d_lock.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>

1 files changed, 15 insertions, 14 deletions

diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 2feb624b67f1..b0ade2d46805 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -87,7 +87,7 @@ full_name_hash(const unsigned char *name, unsigned int len)
 #endif
 
 struct dentry {
-        atomic_t d_count;
+        unsigned int d_count;           /* protected by d_lock */
         unsigned int d_flags;           /* protected by d_lock */
         spinlock_t d_lock;              /* per dentry lock */
         int d_mounted;
@@ -297,17 +297,28 @@ extern char *dentry_path(struct dentry *, char *, int);
  *      needs and they take necessary precautions) you should hold dcache_lock
  *      and call dget_locked() instead of dget().
  */
- 
+static inline struct dentry *dget_dlock(struct dentry *dentry)
+{
+        if (dentry) {
+                BUG_ON(!dentry->d_count);
+                dentry->d_count++;
+        }
+        return dentry;
+}
 static inline struct dentry *dget(struct dentry *dentry)
 {
         if (dentry) {
-                BUG_ON(!atomic_read(&dentry->d_count));
-                atomic_inc(&dentry->d_count);
+                spin_lock(&dentry->d_lock);
+                dget_dlock(dentry);
+                spin_unlock(&dentry->d_lock);
         }
         return dentry;
 }
 
 extern struct dentry * dget_locked(struct dentry *);
+extern struct dentry * dget_locked_dlock(struct dentry *);
+
+extern struct dentry *dget_parent(struct dentry *dentry);
 
 /**
  *      d_unhashed -    is dentry hashed
@@ -338,16 +349,6 @@ static inline void dont_mount(struct dentry *dentry)
         spin_unlock(&dentry->d_lock);
 }
 
-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)