fs: Convert nr_inodes and nr_unused to per-cpu counters

The number of inodes allocated does not need to be tied to the
addition or removal of an inode to/from a list. If we are not tied
to a list lock, we could update the counters when inodes are
initialised or destroyed, but to do that we need to convert the
counters to be per-cpu (i.e. independent of a lock). This means that
we have the freedom to change the list/locking implementation
without needing to care about the counters.

Based on a patch originally from Eric Dumazet.

[AV: cleaned up a bit, fixed build breakage on weird configs

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

3 files changed, 48 insertions, 22 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 39f44f2e709a..f04d04af84f2 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -723,7 +723,7 @@ static long wb_check_old_data_flush(struct bdi_writeback *wb)
         wb->last_old_flush = jiffies;
         nr_pages = global_page_state(NR_FILE_DIRTY) +
                         global_page_state(NR_UNSTABLE_NFS) +
-                        (inodes_stat.nr_inodes - inodes_stat.nr_unused);
+                        get_nr_dirty_inodes();
 
         if (nr_pages) {
                 struct wb_writeback_work work = {
@@ -1090,8 +1090,7 @@ void writeback_inodes_sb(struct super_block *sb)
 
         WARN_ON(!rwsem_is_locked(&sb->s_umount));
 
-        work.nr_pages = nr_dirty + nr_unstable +
-                        (inodes_stat.nr_inodes - inodes_stat.nr_unused);
+        work.nr_pages = nr_dirty + nr_unstable + get_nr_dirty_inodes();
 
         bdi_queue_work(sb->s_bdi, &work);
         wait_for_completion(&done);
diff --git a/fs/inode.c b/fs/inode.c
index 4440cf1034ec..0d5aeccbdd90 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -103,8 +103,41 @@ static DECLARE_RWSEM(iprune_sem);
  */
 struct inodes_stat_t inodes_stat;
 
+static struct percpu_counter nr_inodes __cacheline_aligned_in_smp;
+static struct percpu_counter nr_inodes_unused __cacheline_aligned_in_smp;
+
 static struct kmem_cache *inode_cachep __read_mostly;
 
+static inline int get_nr_inodes(void)
+{
+        return percpu_counter_sum_positive(&nr_inodes);
+}
+
+static inline int get_nr_inodes_unused(void)
+{
+        return percpu_counter_sum_positive(&nr_inodes_unused);
+}
+
+int get_nr_dirty_inodes(void)
+{
+        int nr_dirty = get_nr_inodes() - get_nr_inodes_unused();
+        return nr_dirty > 0 ? nr_dirty : 0;
+
+}
+
+/*
+ * Handle nr_inode sysctl
+ */
+#ifdef CONFIG_SYSCTL
+int proc_nr_inodes(ctl_table *table, int write,
+                   void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+        inodes_stat.nr_inodes = get_nr_inodes();
+        inodes_stat.nr_unused = get_nr_inodes_unused();
+        return proc_dointvec(table, write, buffer, lenp, ppos);
+}
+#endif
+
 static void wake_up_inode(struct inode *inode)
 {
         /*
@@ -192,6 +225,8 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
         inode->i_fsnotify_mask = 0;
 #endif
 
+        percpu_counter_inc(&nr_inodes);
+
         return 0;
 out:
         return -ENOMEM;
@@ -232,6 +267,7 @@ void __destroy_inode(struct inode *inode)
         if (inode->i_default_acl && inode->i_default_acl != ACL_NOT_CACHED)
                 posix_acl_release(inode->i_default_acl);
 #endif
+        percpu_counter_dec(&nr_inodes);
 }
 EXPORT_SYMBOL(__destroy_inode);
 
@@ -286,7 +322,7 @@ void __iget(struct inode *inode)
 
         if (!(inode->i_state & (I_DIRTY|I_SYNC)))
                 list_move(&inode->i_list, &inode_in_use);
-        inodes_stat.nr_unused--;
+        percpu_counter_dec(&nr_inodes_unused);
 }
 
 void end_writeback(struct inode *inode)
@@ -327,8 +363,6 @@ static void evict(struct inode *inode)
  */
 static void dispose_list(struct list_head *head)
 {
-        int nr_disposed = 0;
-
         while (!list_empty(head)) {
                 struct inode *inode;
 
@@ -344,11 +378,7 @@ static void dispose_list(struct list_head *head)
 
                 wake_up_inode(inode);
                 destroy_inode(inode);
-                nr_disposed++;
         }
-        spin_lock(&inode_lock);
-        inodes_stat.nr_inodes -= nr_disposed;
-        spin_unlock(&inode_lock);
 }
 
 /*
@@ -357,7 +387,7 @@ static void dispose_list(struct list_head *head)
 static int invalidate_list(struct list_head *head, struct list_head *dispose)
 {
         struct list_head *next;
-        int busy = 0, count = 0;
+        int busy = 0;
 
         next = head->next;
         for (;;) {
@@ -383,13 +413,11 @@ static int invalidate_list(struct list_head *head, struct list_head *dispose)
                         list_move(&inode->i_list, dispose);
                         WARN_ON(inode->i_state & I_NEW);
                         inode->i_state |= I_FREEING;
-                        count++;
+                        percpu_counter_dec(&nr_inodes_unused);
                         continue;
                 }
                 busy = 1;
         }
-        /* only unused inodes may be cached with i_count zero */
-        inodes_stat.nr_unused -= count;
         return busy;
 }
 
@@ -447,7 +475,6 @@ static int can_unuse(struct inode *inode)
 static void prune_icache(int nr_to_scan)
 {
         LIST_HEAD(freeable);
-        int nr_pruned = 0;
         int nr_scanned;
         unsigned long reap = 0;
 
@@ -483,9 +510,8 @@ static void prune_icache(int nr_to_scan)
                 list_move(&inode->i_list, &freeable);
                 WARN_ON(inode->i_state & I_NEW);
                 inode->i_state |= I_FREEING;
-                nr_pruned++;
+                percpu_counter_dec(&nr_inodes_unused);
         }
-        inodes_stat.nr_unused -= nr_pruned;
         if (current_is_kswapd())
                 __count_vm_events(KSWAPD_INODESTEAL, reap);
         else
@@ -517,7 +543,7 @@ static int shrink_icache_memory(struct shrinker *shrink, int nr, gfp_t gfp_mask)
                         return -1;
                 prune_icache(nr);
         }
-        return (inodes_stat.nr_unused / 100) * sysctl_vfs_cache_pressure;
+        return (get_nr_inodes_unused() / 100) * sysctl_vfs_cache_pressure;
 }
 
 static struct shrinker icache_shrinker = {
@@ -594,7 +620,6 @@ static inline void
 __inode_add_to_lists(struct super_block *sb, struct hlist_head *head,
                         struct inode *inode)
 {
-        inodes_stat.nr_inodes++;
         list_add(&inode->i_list, &inode_in_use);
         list_add(&inode->i_sb_list, &sb->s_inodes);
         if (head)
@@ -1214,7 +1239,7 @@ static void iput_final(struct inode *inode)
         if (!drop) {
                 if (!(inode->i_state & (I_DIRTY|I_SYNC)))
                         list_move(&inode->i_list, &inode_unused);
-                inodes_stat.nr_unused++;
+                percpu_counter_inc(&nr_inodes_unused);
                 if (sb->s_flags & MS_ACTIVE) {
                         spin_unlock(&inode_lock);
                         return;
@@ -1226,14 +1251,13 @@ static void iput_final(struct inode *inode)
                 spin_lock(&inode_lock);
                 WARN_ON(inode->i_state & I_NEW);
                 inode->i_state &= ~I_WILL_FREE;
-                inodes_stat.nr_unused--;
+                percpu_counter_dec(&nr_inodes_unused);
                 hlist_del_init(&inode->i_hash);
         }
         list_del_init(&inode->i_list);
         list_del_init(&inode->i_sb_list);
         WARN_ON(inode->i_state & I_NEW);
         inode->i_state |= I_FREEING;
-        inodes_stat.nr_inodes--;
         spin_unlock(&inode_lock);
         evict(inode);
         spin_lock(&inode_lock);
@@ -1502,6 +1526,8 @@ void __init inode_init(void)
                                          SLAB_MEM_SPREAD),
                                          init_once);
         register_shrinker(&icache_shrinker);
+        percpu_counter_init(&nr_inodes, 0);
+        percpu_counter_init(&nr_inodes_unused, 0);
 
         /* Hash may have been set up in inode_init_early */
         if (!hashdist)
diff --git a/fs/internal.h b/fs/internal.h
index f6dce46d80dc..4cc67eb6ed56 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -105,4 +105,5 @@ extern void release_open_intent(struct nameidata *);
 /*
  * inode.c
  */
+extern int get_nr_dirty_inodes(void);
 extern int invalidate_inodes(struct super_block *);