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>

1 files changed, 23 insertions, 26 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index e987ad576a39..cc2b93802179 100644
--- 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);
                 }
 
                 /*