fs: use RCU in shrink_dentry_list to reduce lock nesting

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

1 files changed, 25 insertions, 21 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index fe8f28a2878e..d1840b30c673 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -615,16 +615,16 @@ static void shrink_dentry_list(struct list_head *list)
 {
         struct dentry *dentry;
 
-        while (!list_empty(list)) {
+        rcu_read_lock();
+        for (;;) {
                 struct dentry *parent;
 
-                dentry = list_entry(list->prev, struct dentry, d_lru);
-
-                if (!spin_trylock(&dentry->d_lock)) {
-relock1:
-                        spin_unlock(&dcache_lru_lock);
-                        cpu_relax();
-                        spin_lock(&dcache_lru_lock);
+                dentry = list_entry_rcu(list->prev, struct dentry, d_lru);
+                if (&dentry->d_lru == list)
+                        break; /* empty */
+                spin_lock(&dentry->d_lock);
+                if (dentry != list_entry(list->prev, struct dentry, d_lru)) {
+                        spin_unlock(&dentry->d_lock);
                         continue;
                 }
 
@@ -634,14 +634,16 @@ relock1:
                  * it - just keep it off the LRU list.
                  */
                 if (dentry->d_count) {
-                        __dentry_lru_del(dentry);
+                        dentry_lru_del(dentry);
                         spin_unlock(&dentry->d_lock);
                         continue;
                 }
+
                 if (!spin_trylock(&dcache_inode_lock)) {
-relock2:
+relock:
                         spin_unlock(&dentry->d_lock);
-                        goto relock1;
+                        cpu_relax();
+                        continue;
                 }
                 if (IS_ROOT(dentry))
                         parent = NULL;
@@ -649,15 +651,15 @@ relock2:
                         parent = dentry->d_parent;
                 if (parent && !spin_trylock(&parent->d_lock)) {
                         spin_unlock(&dcache_inode_lock);
-                        goto relock2;
+                        goto relock;
                 }
-                __dentry_lru_del(dentry);
-                spin_unlock(&dcache_lru_lock);
+                dentry_lru_del(dentry);
 
+                rcu_read_unlock();
                 prune_one_dentry(dentry, parent);
-                /* dcache_inode_lock and dentry->d_lock dropped */
-                spin_lock(&dcache_lru_lock);
+                rcu_read_lock();
         }
+        rcu_read_unlock();
 }
 
 /**
@@ -705,15 +707,15 @@ relock:
                         if (!--cnt)
                                 break;
                 }
-                /* XXX: re-add cond_resched_lock when dcache_lock goes away */
+                cond_resched_lock(&dcache_lru_lock);
         }
-
-        *count = cnt;
-        shrink_dentry_list(&tmp);
-
         if (!list_empty(&referenced))
                 list_splice(&referenced, &sb->s_dentry_lru);
         spin_unlock(&dcache_lru_lock);
+
+        shrink_dentry_list(&tmp);
+
+        *count = cnt;
 }
 
 /**
@@ -805,7 +807,9 @@ void shrink_dcache_sb(struct super_block *sb)
         spin_lock(&dcache_lru_lock);
         while (!list_empty(&sb->s_dentry_lru)) {
                 list_splice_init(&sb->s_dentry_lru, &tmp);
+                spin_unlock(&dcache_lru_lock);
                 shrink_dentry_list(&tmp);
+                spin_lock(&dcache_lru_lock);
         }
         spin_unlock(&dcache_lru_lock);
 }