fs: clean up dentry lru modification

Always do a list_del_init on the LRU to make sure the list_empty invariant for
not beeing on the LRU always holds true, and fold dentry_lru_del_init into
dentry_lru_del.  Replace the dentry_lru_add_tail primitive with a
dentry_lru_move_tail operations that simpler when the dentry already is one
the list, which is always is.  Move the list_empty into dentry_lru_add to
fit the scheme of the other lru helpers, and simplify locking once we
move to a separate LRU lock.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/dcache.c b/fs/dcache.c
index e987ad576a397c79d13f973538985578896b615b..cc2b938021796c0a8d4492030043309f087f790e 100644 (file)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -133,37 +133,34 @@ static void dentry_iput(struct dentry * dentry)
 }
 
 /*
- * dentry_lru_(add|add_tail|del|del_init) must be called with dcache_lock held.
+ * dentry_lru_(add|del|move_tail) must be called with dcache_lock held.
  */
 static void dentry_lru_add(struct dentry *dentry)
 {
-       list_add(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
-       dentry->d_sb->s_nr_dentry_unused++;
-       percpu_counter_inc(&nr_dentry_unused);
-}
-
-static void dentry_lru_add_tail(struct dentry *dentry)
-{
-       list_add_tail(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
-       dentry->d_sb->s_nr_dentry_unused++;
-       percpu_counter_inc(&nr_dentry_unused);
+       if (list_empty(&dentry->d_lru)) {
+               list_add(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
+               dentry->d_sb->s_nr_dentry_unused++;
+               percpu_counter_inc(&nr_dentry_unused);
+       }
 }
 
 static void dentry_lru_del(struct dentry *dentry)
 {
        if (!list_empty(&dentry->d_lru)) {
-               list_del(&dentry->d_lru);
+               list_del_init(&dentry->d_lru);
                dentry->d_sb->s_nr_dentry_unused--;
                percpu_counter_dec(&nr_dentry_unused);
        }
 }
 
-static void dentry_lru_del_init(struct dentry *dentry)
+static void dentry_lru_move_tail(struct dentry *dentry)
 {
-       if (likely(!list_empty(&dentry->d_lru))) {
-               list_del_init(&dentry->d_lru);
-               dentry->d_sb->s_nr_dentry_unused--;
-               percpu_counter_dec(&nr_dentry_unused);
+       if (list_empty(&dentry->d_lru)) {
+               list_add_tail(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
+               dentry->d_sb->s_nr_dentry_unused++;
+               percpu_counter_inc(&nr_dentry_unused);
+       } else {
+               list_move_tail(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
        }
 }
 
@@ -253,8 +250,7 @@ repeat:
 
        /* Otherwise leave it cached and ensure it's on the LRU */
        dentry->d_flags |= DCACHE_REFERENCED;
-       if (list_empty(&dentry->d_lru))
-               dentry_lru_add(dentry);
+       dentry_lru_add(dentry);
 
        spin_unlock(&dentry->d_lock);
        spin_unlock(&dcache_lock);
@@ -333,7 +329,7 @@ EXPORT_SYMBOL(d_invalidate);
 static inline struct dentry * __dget_locked(struct dentry *dentry)
 {
        atomic_inc(&dentry->d_count);
-       dentry_lru_del_init(dentry);
+       dentry_lru_del(dentry);
        return dentry;
 }
 
@@ -452,7 +448,7 @@ static void prune_one_dentry(struct dentry * dentry)
 
                if (dentry->d_op && dentry->d_op->d_delete)
                        dentry->d_op->d_delete(dentry);
-               dentry_lru_del_init(dentry);
+               dentry_lru_del(dentry);
                __d_drop(dentry);
                dentry = d_kill(dentry);
                spin_lock(&dcache_lock);
@@ -465,7 +461,7 @@ static void shrink_dentry_list(struct list_head *list)
 
        while (!list_empty(list)) {
                dentry = list_entry(list->prev, struct dentry, d_lru);
-               dentry_lru_del_init(dentry);
+               dentry_lru_del(dentry);
 
                /*
                 * We found an inuse dentry which was not removed from
@@ -650,7 +646,7 @@ static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
 
        /* detach this root from the system */
        spin_lock(&dcache_lock);
-       dentry_lru_del_init(dentry);
+       dentry_lru_del(dentry);
        __d_drop(dentry);
        spin_unlock(&dcache_lock);
 
@@ -664,7 +660,7 @@ static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
                        spin_lock(&dcache_lock);
                        list_for_each_entry(loop, &dentry->d_subdirs,
                                            d_u.d_child) {
-                               dentry_lru_del_init(loop);
+                               dentry_lru_del(loop);
                                __d_drop(loop);
                                cond_resched_lock(&dcache_lock);
                        }
@@ -841,14 +837,15 @@ resume:
                struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);
                next = tmp->next;
 
-               dentry_lru_del_init(dentry);
                /* 
                 * move only zero ref count dentries to the end 
                 * of the unused list for prune_dcache
                 */
                if (!atomic_read(&dentry->d_count)) {
-                       dentry_lru_add_tail(dentry);
+                       dentry_lru_move_tail(dentry);
                        found++;
+               } else {
+                       dentry_lru_del(dentry);
                }
 
                /*