dentry: move to per-sb LRU locks

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@openvz.org: updated changelog ]
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Glauber Costa <glommer@openvz.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Carlos Maiolino <cmaiolino@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: David Rientjes <rientjes@google.com>
Cc: Gleb Natapov <gleb@redhat.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: J. Bruce Fields <bfields@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Kent Overstreet <koverstreet@google.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

3 files changed, 20 insertions, 18 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index 03161240e744..e989ecb44a65 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);
@@ -362,12 +361,12 @@ static void dentry_unlink_inode(struct dentry * dentry)
 static void dentry_lru_add(struct dentry *dentry)
 {
         if (unlikely(!(dentry->d_flags & DCACHE_LRU_LIST))) {
-                spin_lock(&dcache_lru_lock);
+                spin_lock(&dentry->d_sb->s_dentry_lru_lock);
                 dentry->d_flags |= DCACHE_LRU_LIST;
                 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);
         }
 }
 
@@ -385,15 +384,15 @@ 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)) {
                 dentry->d_flags |= DCACHE_LRU_LIST;
                 list_add_tail(&dentry->d_lru, list);
@@ -402,7 +401,7 @@ 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);
 }
 
 /**
@@ -895,14 +894,14 @@ 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;
                 }
@@ -918,11 +917,11 @@ 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);
 }
@@ -938,14 +937,14 @@ 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 63b6863bac7b..3c5318694ccd 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -176,6 +176,7 @@ 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 3b3edac75df2..14a90f6886fa 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1269,7 +1269,9 @@ 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 */