unify dentry_iput() and dentry_unlink_inode()

There is a lot of duplication between dentry_unlink_inode() and dentry_iput().
The only real difference is that dentry_unlink_inode() bumps ->d_seq and
dentry_iput() doesn't.  The argument of the latter is known to have been
unhashed, so anybody who might've found it in RCU lookup would already be
doomed to a ->d_seq mismatch.  And we want to avoid pointless smp_rmb() there.

This patch makes dentry_unlink_inode() bump ->d_seq only for hashed dentries.
It's safe (d_delete() calls that sucker only if we are holding the only
reference to dentry, so rehash is not going to happen) and it allows
to use dentry_unlink_inode() in __dentry_kill() and get rid of dentry_iput().

The interesting question here is profiling; it *is* a hot path, and extra
conditional jumps in there might or might not be painful.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/dcache.c b/fs/dcache.c
index f9c63c1..fe7cde2 100644 (file)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -335,44 +335,21 @@ static inline void dentry_rcuwalk_invalidate(struct dentry *dentry)
 
 /*
  * Release the dentry's inode, using the filesystem
- * d_iput() operation if defined. Dentry has no refcount
- * and is unhashed.
- */
-static void dentry_iput(struct dentry * dentry)
-       __releases(dentry->d_lock)
-       __releases(dentry->d_inode->i_lock)
-{
-       struct inode *inode = dentry->d_inode;
-       if (inode) {
-               __d_clear_type_and_inode(dentry);
-               hlist_del_init(&dentry->d_u.d_alias);
-               spin_unlock(&dentry->d_lock);
-               spin_unlock(&inode->i_lock);
-               if (!inode->i_nlink)
-                       fsnotify_inoderemove(inode);
-               if (dentry->d_op && dentry->d_op->d_iput)
-                       dentry->d_op->d_iput(dentry, inode);
-               else
-                       iput(inode);
-       } else {
-               spin_unlock(&dentry->d_lock);
-       }
-}
-
-/*
- * Release the dentry's inode, using the filesystem
- * d_iput() operation if defined. dentry remains in-use.
+ * d_iput() operation if defined.
  */
 static void dentry_unlink_inode(struct dentry * dentry)
        __releases(dentry->d_lock)
        __releases(dentry->d_inode->i_lock)
 {
        struct inode *inode = dentry->d_inode;
+       bool hashed = !d_unhashed(dentry);
 
-       raw_write_seqcount_begin(&dentry->d_seq);
+       if (hashed)
+               raw_write_seqcount_begin(&dentry->d_seq);
        __d_clear_type_and_inode(dentry);
        hlist_del_init(&dentry->d_u.d_alias);
-       raw_write_seqcount_end(&dentry->d_seq);
+       if (hashed)
+               raw_write_seqcount_end(&dentry->d_seq);
        spin_unlock(&dentry->d_lock);
        spin_unlock(&inode->i_lock);
        if (!inode->i_nlink)
@@ -540,12 +517,10 @@ static void __dentry_kill(struct dentry *dentry)
        dentry->d_flags |= DCACHE_DENTRY_KILLED;
        if (parent)
                spin_unlock(&parent->d_lock);
-       dentry_iput(dentry);
-       /*
-        * dentry_iput drops the locks, at which point nobody (except
-        * transient RCU lookups) can reach this dentry.
-        */
-       BUG_ON(dentry->d_lockref.count > 0);
+       if (dentry->d_inode)
+               dentry_unlink_inode(dentry);
+       else
+               spin_unlock(&dentry->d_lock);
        this_cpu_dec(nr_dentry);
        if (dentry->d_op && dentry->d_op->d_release)
                dentry->d_op->d_release(dentry);