[PATCH v11 04/25] dentry: move to per-sb LRU locks

[Glauber Costa <glommer-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>]

From: Dave Chinner <dchinner-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>

With the dentry LRUs being per-sb structures, there is no real need for
a global dentry_lru_lock. The locking can be made more fine-grained by
moving to a per-sb LRU lock, isolating the LRU operations of different
filesytsems completely from each other. The need for this is independent
of any performance consideration that may arise: in the interest of
abstracting the lru operations away, it is mandatory that each lru works
around its own lock instead of a global lock for all of them.

[ glommer: updated changelog ]
Signed-off-by: Dave Chinner <dchinner-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Signed-off-by: Glauber Costa <glommer-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>
Reviewed-by: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>
Acked-by: Mel Gorman <mgorman-l3A5Bk7waGM@public.gmane.org>
---
 fs/dcache.c        | 33 ++++++++++++++++-----------------
 fs/super.c         |  1 +
 include/linux/fs.h |  4 +++-
 3 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 0466dbd..0a49669 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -48,7 +48,7 @@
  *   - the dcache hash table
  * s_anon bl list spinlock protects:
  *   - the s_anon list (see __d_drop)
- * dcache_lru_lock protects:
+ * dentry->d_sb->s_dentry_lru_lock protects:
  *   - the dcache lru lists and counters
  * d_lock protects:
  *   - d_flags
@@ -63,7 +63,7 @@
  * Ordering:
  * dentry->d_inode->i_lock
  *   dentry->d_lock
- *     dcache_lru_lock
+ *     dentry->d_sb->s_dentry_lru_lock
  *     dcache_hash_bucket lock
  *     s_anon lock
  *
@@ -81,7 +81,6 @@
 int sysctl_vfs_cache_pressure __read_mostly = 100;
 EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);
 
-static __cacheline_aligned_in_smp DEFINE_SPINLOCK(dcache_lru_lock);
 __cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);
 
 EXPORT_SYMBOL(rename_lock);
@@ -333,11 +332,11 @@ static void dentry_unlink_inode(struct dentry * dentry)
 static void dentry_lru_add(struct dentry *dentry)
 {
 	if (list_empty(&dentry->d_lru)) {
-		spin_lock(&dcache_lru_lock);
+		spin_lock(&dentry->d_sb->s_dentry_lru_lock);
 		list_add(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
 		dentry->d_sb->s_nr_dentry_unused++;
 		this_cpu_inc(nr_dentry_unused);
-		spin_unlock(&dcache_lru_lock);
+		spin_unlock(&dentry->d_sb->s_dentry_lru_lock);
 	}
 }
 
@@ -355,15 +354,15 @@ static void __dentry_lru_del(struct dentry *dentry)
 static void dentry_lru_del(struct dentry *dentry)
 {
 	if (!list_empty(&dentry->d_lru)) {
-		spin_lock(&dcache_lru_lock);
+		spin_lock(&dentry->d_sb->s_dentry_lru_lock);
 		__dentry_lru_del(dentry);
-		spin_unlock(&dcache_lru_lock);
+		spin_unlock(&dentry->d_sb->s_dentry_lru_lock);
 	}
 }
 
 static void dentry_lru_move_list(struct dentry *dentry, struct list_head *list)
 {
-	spin_lock(&dcache_lru_lock);
+	spin_lock(&dentry->d_sb->s_dentry_lru_lock);
 	if (list_empty(&dentry->d_lru)) {
 		list_add_tail(&dentry->d_lru, list);
 		dentry->d_sb->s_nr_dentry_unused++;
@@ -371,7 +370,7 @@ static void dentry_lru_move_list(struct dentry *dentry, struct list_head *list)
 	} else {
 		list_move_tail(&dentry->d_lru, list);
 	}
-	spin_unlock(&dcache_lru_lock);
+	spin_unlock(&dentry->d_sb->s_dentry_lru_lock);
 }
 
 /**
@@ -851,14 +850,14 @@ void prune_dcache_sb(struct super_block *sb, int count)
 	LIST_HEAD(tmp);
 
 relock:
-	spin_lock(&dcache_lru_lock);
+	spin_lock(&sb->s_dentry_lru_lock);
 	while (!list_empty(&sb->s_dentry_lru)) {
 		dentry = list_entry(sb->s_dentry_lru.prev,
 				struct dentry, d_lru);
 		BUG_ON(dentry->d_sb != sb);
 
 		if (!spin_trylock(&dentry->d_lock)) {
-			spin_unlock(&dcache_lru_lock);
+			spin_unlock(&sb->s_dentry_lru_lock);
 			cpu_relax();
 			goto relock;
 		}
@@ -874,11 +873,11 @@ relock:
 			if (!--count)
 				break;
 		}
-		cond_resched_lock(&dcache_lru_lock);
+		cond_resched_lock(&sb->s_dentry_lru_lock);
 	}
 	if (!list_empty(&referenced))
 		list_splice(&referenced, &sb->s_dentry_lru);
-	spin_unlock(&dcache_lru_lock);
+	spin_unlock(&sb->s_dentry_lru_lock);
 
 	shrink_dentry_list(&tmp);
 }
@@ -894,14 +893,14 @@ void shrink_dcache_sb(struct super_block *sb)
 {
 	LIST_HEAD(tmp);
 
-	spin_lock(&dcache_lru_lock);
+	spin_lock(&sb->s_dentry_lru_lock);
 	while (!list_empty(&sb->s_dentry_lru)) {
 		list_splice_init(&sb->s_dentry_lru, &tmp);
-		spin_unlock(&dcache_lru_lock);
+		spin_unlock(&sb->s_dentry_lru_lock);
 		shrink_dentry_list(&tmp);
-		spin_lock(&dcache_lru_lock);
+		spin_lock(&sb->s_dentry_lru_lock);
 	}
-	spin_unlock(&dcache_lru_lock);
+	spin_unlock(&sb->s_dentry_lru_lock);
 }
 EXPORT_SYMBOL(shrink_dcache_sb);
 
diff --git a/fs/super.c b/fs/super.c
index 2a37fd6..0be75fb 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -182,6 +182,7 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags)
 		INIT_HLIST_BL_HEAD(&s->s_anon);
 		INIT_LIST_HEAD(&s->s_inodes);
 		INIT_LIST_HEAD(&s->s_dentry_lru);
+		spin_lock_init(&s->s_dentry_lru_lock);
 		INIT_LIST_HEAD(&s->s_inode_lru);
 		spin_lock_init(&s->s_inode_lru_lock);
 		INIT_LIST_HEAD(&s->s_mounts);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index ad3eb76..41cbe7a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1264,7 +1264,9 @@ struct super_block {
 	struct list_head	s_files;
 #endif
 	struct list_head	s_mounts;	/* list of mounts; _not_ for fs use */
-	/* s_dentry_lru, s_nr_dentry_unused protected by dcache.c lru locks */
+
+	/* s_dentry_lru_lock protects s_dentry_lru and s_nr_dentry_unused */
+	spinlock_t		s_dentry_lru_lock ____cacheline_aligned_in_smp;
 	struct list_head	s_dentry_lru;	/* unused dentry lru */
 	long			s_nr_dentry_unused;	/* # of dentry on lru */
 
-- 
1.8.1.4