fs: use RCU in shrink_dentry_list to reduce lock nesting

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

diff --git a/fs/dcache.c b/fs/dcache.c
index fe8f28a2878eed71fc175d5fcb89707e5f6f4924..d1840b30c6731deba0f89f049b681d2285adbe96 100644 (file)
--- 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);
 }