inode: convert inode_stat.nr_unused to per-cpu counters

Before we split up the inode_lru_lock, the unused inode counter
needs to be made independent of the global inode_lru_lock. Convert
it to per-cpu counters to do this.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/inode.c

@@ -95,6 +95,7 @@ EXPORT_SYMBOL(empty_aops);
 struct inodes_stat_t inodes_stat;
 
 static DEFINE_PER_CPU(unsigned int, nr_inodes);
+static DEFINE_PER_CPU(unsigned int, nr_unused);
 
 static struct kmem_cache *inode_cachep __read_mostly;
 
@@ -109,7 +110,11 @@ static int get_nr_inodes(void)
 
 static inline int get_nr_inodes_unused(void)
 {
-	return inodes_stat.nr_unused;
+	int i;
+	int sum = 0;
+	for_each_possible_cpu(i)
+		sum += per_cpu(nr_unused, i);
+	return sum < 0 ? 0 : sum;
 }
 
 int get_nr_dirty_inodes(void)
@@ -127,6 +132,7 @@ 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
@@ -340,7 +346,7 @@ static void inode_lru_list_add(struct inode *inode)
 	spin_lock(&inode_lru_lock);
 	if (list_empty(&inode->i_lru)) {
 		list_add(&inode->i_lru, &inode_lru);
-		inodes_stat.nr_unused++;
+		this_cpu_inc(nr_unused);
 	}
 	spin_unlock(&inode_lru_lock);
 }
@@ -350,7 +356,7 @@ static void inode_lru_list_del(struct inode *inode)
 	spin_lock(&inode_lru_lock);
 	if (!list_empty(&inode->i_lru)) {
 		list_del_init(&inode->i_lru);
-		inodes_stat.nr_unused--;
+		this_cpu_dec(nr_unused);
 	}
 	spin_unlock(&inode_lru_lock);
 }
@@ -656,7 +662,7 @@ static void prune_icache(int nr_to_scan)
 		    (inode->i_state & ~I_REFERENCED)) {
 			list_del_init(&inode->i_lru);
 			spin_unlock(&inode->i_lock);
-			inodes_stat.nr_unused--;
+			this_cpu_dec(nr_unused);
 			continue;
 		}
 
@@ -693,7 +699,7 @@ static void prune_icache(int nr_to_scan)
 		spin_unlock(&inode->i_lock);
 
 		list_move(&inode->i_lru, &freeable);
-		inodes_stat.nr_unused--;
+		this_cpu_dec(nr_unused);
 	}
 	if (current_is_kswapd())
 		__count_vm_events(KSWAPD_INODESTEAL, reap);